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Introduction 1
CHAPTER 1.
INTRODUCTION
1.1 Context and purpose
Horses were domesticated about 2,500 to 5,000-years ago (Clutton-Brock 1981).
Domesticated animals that return to a wild state independent from humans and are capable
of reproducing and sustaining a population are termed feral animals (McKnight 1976). In the
United States of America (USA), feral horses persist because they have (Berger 1986):
(1) flexible behavioural and physiological systems that enable them to adapt and reproduce
under a broad spectrum of ecological conditions; (2) occupy isolated, remote habitats; and
(3) are legally protected and regarded as a ‘national treasure’ that embodies ‘the historic and
pioneer spirit of the west’, under the Wild Free-Roaming Horses and Burro Act 1971 (Wagner
1983; Rutberg 2003). In Australia, feral horses inhabit a range of environments from deserts
to wetlands, and tend to be most abundant in the remote unfenced cattle production areas
of the northern states and in rugged mountainous country (Symanksi 1994; Csurhes et al.
2009). Unlike the USA, feral horses are not protected by legislation and in South Australia,
for example, are declared a pest species under the Natural Resources Management Act 2004
(Dawson et al. 2006). The majority of populations exist on public lands of conservation value
where government authorities such as the National Parks and Wildlife Service (NPWS) have
statutory obligations to reduce population numbers (English 2001b; Edwards et al. 2003).
However, many Australians and several public interest groups (e.g. Save the Brumbies,
Australian Brumby Alliance) either do not perceive feral horses as a pest species or regard
them as an iconic species of cultural and heritage significance that should be managed for
preservation in accordance with their status in the USA (Walter 2002; Ballard 2005; Finch and
Baxter 2007; Nimmo and Miller 2007; Nimmo et al. 2007).
Horse population control thus continues to be one of the most complicated problems
for wildlife management agencies worldwide due to multiple, often highly emotional, and
polarised attitudes of stakeholders (Wolfe 1980; Rikoon and Albee 1998; Rikoon 2006;
Hubert and Klein 2007; Kincaid 2008; Taggart 2008). These contrasting views were
epitomised by the public reaction to the aerial (helicopter) cull of 606 horses in Guy Fawkes
River National Park (GFRNP), New South Wales (NSW), in October 2000. Ballard (2005)
concluded that rarely has a wildlife management issue in Australia received such a sustained
level of public acrimony, domestic and international media coverage, and political
Introduction 2
involvement as the GFRNP cull. The direct ramifications of the cull were considerable and
included an official review of the GFRNP culling operation and horse management in all NSW
National Parks (English 2000, 2001b), a NSW Local Court case with 12 counts of animal
cruelty filed against the NPWS (NSW NPWS 2002), parliamentary allegations of corruption
(Fraser 2002) and a permanent ban on the aerial culling of horses in national parks in NSW
(AAP 2000), and the development of a management plan for the remaining horses in GFRNP
(English 2001a; NSW NPWS 2003). The critical points of contention in horse control are the
heritage value of the Australian ‘brumby’ versus the adverse effects of horses on the
environment and native wildlife. To date, no scientific studies on the ecological effects of
horses on Australian ecosystems have been published in peer-reviewed literature, despite
Australia reputedly having the largest population of feral horses world-wide at an estimated
300,000 to 600,000 individuals (Dobbie et al. 1993; Dawson et al. 2006). After the GFRNP
cull, the then NSW Minister for the Environment established a Heritage Working Party (HWP)
to determine the heritage value of the horses in GFRNP (Heritage Working Party 2002a). In
concordance with the official review (English 2001b), the Minister also directed the NPWS to
monitor the environmental impacts in GFRNP associated with horses (Debus 2002).
The purpose of this thesis is to independently assess the impact of feral horses on
select plant communities, soil properties and grazing native mammals (i.e. macropods) in
GFRNP. The results are discussed in relation to the knowledge of horse impacts elsewhere in
Australia and overseas and the implications for future management efforts.
1.2 Horse evolution and definitions
The mammalian family, Equidae (zebras, asses and horses) includes one genus
(Equus) with 18 extant native (wild) species or subspecies that are limited to Africa and Asia,
with a recent reintroduction in parts of Eurasia (Oakenfull et al. 2000). The one horse
species (Equus ferus) has three subspecies: the tarpan or Eurasian wild horse (Equus ferus
ferus), Przewalski’s horse or takhi (Equus ferus przewalskii), which is the only true extant (and
critically endangered) native horse species, and the domestic and feral horse (Equus ferus
caballus) (ICZN 2003). The other domesticated member of Equus is the domestic donkey or
feral ass (Equus africanus or E.asinus) (Oakenfull et al. 2000). The modern genus Equus first
appeared some 2 million years ago in North America from whence they spread to Asia,
Europe, Africa and South America (Kavar and Dovc 2008) to become one of the top four
grazing herbivores of the Pleistocene Mammoth Steppe (Guthrie 1990). Wild equids became
Introduction 3
extinct in North and South America some 8,000–12,000 years ago but survived and
diversified in Asia, Europe and Africa, for example, into numerous species and subspecies of
zebra in Africa inparticular (Martin 1970; Bennet and Hoffmann 1999). In western Europe,
rock engravings resembling the takhi have been dated at 11,000–22,000 years of age in Italy,
western France and northern Spain (Van Dierendonck and Wallis De Vries 1996). Wild horses
are thought to have existed in England until about 700 years ago, in Germany until
2000 years ago, and in Eastern Europe (e.g. Poland, Lithuania and Latvia) until the tarpan
became extinct sometime between 1814 and 1879 (Groves 1991; Levin et al. 2002; Kavar and
Dovc 2008). Some populations of specific breeds of feral horses have thus had an almost
continuous presence in Europe (e.g. Camargue horses in France, Konik polski horses in Latvia
and Poland) (Duncan 1992; Schwartz 2005). In North and South America, domestic horses
were progressively introduced from the early 1500s to 1700s (Darwin 1962; Berger 1986). In
Australia, they were introduced from 1788 onwards and in New Zealand in 1814, with the
first feral population in the Kaimanawa mountain region recorded in 1876 (MacDougall 2001;
Mincham 2008). Thus, evolutionary history may be generally described as long and
continuous in Europe, long but discontinuous in North and South America, and short in
Australasia. Differences in evolutionary history between Europe, both the Americas and
Australasia was described because those regions are where studies of the ecological impact
of feral horses have mostly been conducted (Section 1.4; Appendix 1). The inverse
relationship between the degree of exposure over evolutionary periods to large, generalist
herbivores and the responses of certain plant communities to grazing is an important
explanatory variable in some contemporary global models of grazing impacts (Mack and
Thompson 1982; Milchunas et al. 1988; Mack 1989; Milchunas and Lauenroth 1993). The
evolutionary history of feral horses thus provides a general background for evaluating the
international peer-reviewed literature on the environmental effects of feral horses. It also
provides clarification for terms used in this thesis. For example, coinciding with the heritage
perspective is an objection to the term ‘feral’, with preferences for ‘brumby’, ‘wild’, or
‘free-ranging horses’. Throughout this thesis the term feral horse will be used to describe
Australian populations as this has been independently assessed (English 2001b) as the
ecologically correct description of how horse populations originated and remain in the wild.
The same rationale applies to other populations arising from domestic introductions (i.e. the
Americas and New Zealand). In the interest of brevity, hereafter the term feral horse(s) is
also abbreviated to horse(s) with domestic populations referred to specifically in the context
Introduction 4
required, for example, stockhorse, recreational riding horse or the generic term of domestic
horse. The term ‘wild’ horse is akin to native and also has a specific ecological meaning,
namely ‘a species or race thought to have occurred in a geographical area before the
Neolithic’ (New Stone Age, circa 9500 B.C.; Manchester and Bullock 2000). This definition
only applies to the extant takhi subspecies of horse and the world’s species and subspecies of
‘wild’ equids, of which only the three subspecies of kiang (E. kiang) in Asia and five of the six
subspecies of plains zebra (E. burchelli) in Africa remain abundant and widespread (Duncan
1992).
1.3 Feral horse biology in relation to ecological impact potential
According to the so-called ‘tens rule’ for statistical regularities in biological invasions,
10% of introduced species become established in the wild, and 10% of those established
become a pest (Williamson and Fitter 1996a, b). Pest species are difficult to define (Perrins
et al. 1992) because species are pests for individualistic reasons (Williamson and Fitter
1996b). Across New Zealand and Australia, feral horses are considered a pest species and
have been assigned the same types of impacts as feral pigs (Sus scrofa) and feral goats (Capra
hircus), with the main impact being environmental degradation (Wilson et al. 1992; Cowan
and Tyndale-Biscoe 1997). Aspects of the biology and ecology of feral horses that predispose
the species to having an adverse affect on the environment are outlined in the following
sections. As horse impact studies in Australia are scarce, I also drew on the livestock (i.e.
cattle) grazing literature to develop experimental hypotheses about ungulate impacts
relevant to Australian ecosystems. Consideration was given to cattle (Bos taurus) to validate
the assumption that some environmental impacts associated with cattle in Australia may also
apply to horses with qualifications.
1.3.1 Home range, social organisation and mobility
Feral horse home ranges vary with environmental conditions, mainly the quantity and
quality of available forage biomass and physical barriers to expansion such as mountain
ranges (Rubenstein 1981; McCort 1984). Estimates of home range sizes are generally lower
for island populations (e.g. 90 ha on Sable Island) (Welsh 1975) and higher for semi-arid
populations (e.g. 30300 ha in the Wyoming Red Desert) (Miller 1983; Waring 1983b and
references therein). The estimates of 120 ha, 140 ha and 980 ha for three horses radio-
tracked in GFRNP (NSW NPWS 2006a) concur with those obtained in comparable temperate
Introduction 5
environments, such as New Zealand, and tend to be closer to the estimates for island
populations (59–1768 ha) (Linklater et al. 2000). The higher value for GFRNP was for a
dispersing colt, whereas mature horses in GFRNP, as in central Australia (Dobbie and Berman
1992), do not appear to move willingly from their home range, seasonal movements aside.
Feral horses are group-forming ungulates, with an average group (mob) size of 4.0–
7.7 horses commonly (Waring 1983a), but with multi-male breeding groups of over 30 horses
(herds) possible (Miller and Denniston 1979; Linklater and Cameron 2000). In GFRNP,
average group size has ranged from 4.4 ± 1.8 horses to 5.3 ± 2.6 horses (Vernes et al. 2009).
Feral horses are not typically geographically territorial (Ransom and Cade 2009) and mobs
may share watering, feeding and shelter sites with other mobs within overlapping home
ranges (Waring 1983b). However, stallions defend their mating rights with harem mares
(Rubenstein and Hack 2004) and can exhibit resource-orientated territoriality, particularly if
the resource is high quality or limited in extent (e.g. mineral resources) (Pellegrini 1971;
Bogliani et al. 1994; Ransom et al. 2007). Core areas are those smaller areas within a home
range that are used most frequently and probably include the homesites, refuges, and most
dependable food sources (Kaufmann 1962; Ewer 1968) and thus may be expected to include
sites where the direct consequences of horse activity (e.g. dung, dust wallows, tracks) are
clumped (Walters 1996). In the Kaimanawa horse population, the average (±1 S.E.) core area
(87 ± 8 ha, 50% utilisation) was much smaller than average home range size (539 ± 46 ha,
95% utilisation).
Seasonal movement has been reported in numerous horse populations (e.g. Miller
1980; Ganskopp and Vavra 1986; Crane et al. 1997a; Rheinhardt and Rheinhardt 2004).
However, unlike the abundant wild equids in Africa (e.g. plains zebra on the Serengeti Plain,
Tanzania where up to 280,000 zebras move 100–150 km, Grubb 1981), long-distance
seasonal migration en masse does not occur. Therefore even at lower regional densities,
localised feral horse impacts have the potential to be severe due to continual, concentrated
use by resident individuals within a mob or multiple mobs while systems supporting migrants
are apparently more resilient (Fryxell and Sinclair 1988). The rest periods associated with
migration can play an important part (in addition to fire and evolutionary history) in the long-
term persistence of plant–herbivore systems, particularly in areas with slow rates of
vegetation regeneration (Coughenour 1991; Holdo et al. 2007). Horses also have the
potential to affect a greater range of habitat types across a greater area than cattle due to
their superior mobility and agility. In more xeric habitats, horses travel further from water
Introduction 6
each day and in general, for example, up to 50 km in Central Australia (Pellegrini 1971; Green
and Green 1977; Berman 1991). While cattle walk as far as 25 km, they begin to lose
condition after 7 km (CSIRO 1981). To reduce energy expenditure or due to physical
limitations, cattle generally avoid grazing slopes over 6–11° and slope is an important and
consistent determinant of cattle distributions on mountain rangelands (Roath and Krueger
1982; Gillen et al. 1984; Bailey et al. 1996; Ganskopp et al. 2000). Conversely, in comparative
studies with cattle, it is typical for horses to rapidly traverse rugged or steep topography (up
to 45°) to gain access to relatively flat but elevated grazing terrain or high benches and ridge
tops to enhance the ‘viewshed’ (Pellegrini 1971; Miller 1980; Ganskopp and Vavra 1987).
Thus feral horses are more destructive of elevated, hill country than cattle (Hungerford
1980). Mobility also enables horses to form ‘reserve’ populations in areas inaccessible to
management and immigrate into areas after localised population control, or expand into new
areas if resources become limited due to density-dependent population growth.
1.3.2 High reproductive potential and density-dependent population growth
Early simulations and estimates of finite annual growth rates (λ) from aerial counts of
feral horses in western USA reported growth rates ranging from λ = 1.04 to λ >1.20 (Cook
1975; Conley 1979; NRC 1980; Wolfe 1980, 1986). However, all sources doubted if the high
reproduction and survival rates (>90%) required to produce growth rates around λ = 1.20
(i.e. increasing at 20% annually) are realistic, for reasons outlined in Garrott et al. (1991b), or
questioned the quality of the aerial counts (Frei et al. 1979; Symanski 1996). Similarly, initial
estimates of λ = 1.17–1.24 (Rogers 1991) for Kaimanawa horses in New Zealand were
thought to be exaggerated and revised to an average of λ = 1.10 and a biological maximum of
λ = 1.20 (Linklater et al. 2004), in agreement with Conley (1979). Subsequent studies revised
the age of first foaling from 3–5-years to 2–3-years, and allowed for foals in consecutive
years and annual survival rates of both adults and foals (to 1-year-of-age) have either
approached or exceeded 90% (e.g. Keiper and Houpt 1984), all of which contributed to
annual growth rates not less than λ = 1.15, with most estimates approaching or exceeding
λ = 1.20 for North American mainland and island feral horse populations (Eberhardt et al.
1982; Kirkpatrick and Turner 1986; Garrott and Taylor 1990; Garrott et al. 1991a; Garrott et
al. 1991b and references therein; Garrott et al. 1992; Kirkpatrick and Turner 2003). Even
higher finite annual growth rates have been reported for horses in the French Camargue
(yearly maximum, λ = 1.31, average λ = 1.27; Grange et al. 2009) and Argentina ( λ = 1.33;
Introduction 7
Scorolli and Cazorla 2010), supporting Duncan’s (1992) suggestion that λ values > 1.20 are
possible in feral horse populations. Such extreme rates are more likely at low densities or
over initial introduction periods as in the Camargue and at Lake Pape, Latvia, where the
number of horses doubled in the first 2 years after being released (Prieditis 2002).
Feral horse population growth appears to be density-dependent, possibly due to
social stress but mostly due to food limitation (Scorolli and Cazorla 2010), resulting in lower
growth rates (e.g. λ = 1.03–1.07; Goodloe et al. 2000). Thus, even if high-density populations
fall or ‘crash’, it would be after most of the available forage biomass has been removed, as
occurred with the Camargue and Lake Pape re-introductions, with potential consequences
for other wildlife and ecosystem processes (Duncan 1992; Prieditis 2002). By reacting to
changes in density, horse populations can also recover quickly from controlled or stochastic
reductions (e.g. severe winters, fire) by marked increases in foaling rates and reproduction at
an earlier age (e.g. Garrott and Taylor 1990).
In Australia, historical counts of horse numbers and population dynamics in the
Northern Territory have been debated (Symanksi 1994). Methods and personnel have been
more consistent in the Australian Alps National Park (AANP), where feral horse population
growth rates have shown recent evidence of density-dependent recovery aided by range
expansion (Walter 2002). After a dramatic population decline between 2001 and 2003,
coinciding with severe and extensive wildfires, the estimated average rate of increase was
21.7% per annum (λ = 1.21) for 2003–2009, which has been associated with the potential for
greater environmental impacts (Dawson 2009a; Booth and Low 2010). While empirical
evidence is lacking for GFRNP, based on the demography of captured horses, the rate of
increase per annum may be as high as 16% (NSW NPWS 2006b). In AANP and GFRNP, growth
rates may be inflated during temporary periods of abundant food supplies, lack of crowding
or range expansion in combination with no appreciable mortality due to disease or
predation. Such conditions have been documented for other large, long-lived mammals with
similar reproductive features as horses (e.g. bison, Bison bison) (Eberhardt 1985; Garrott et
al. 1991b and references therein).
1.3.3 Flexible feeding ecology
The perissodactyls (equids) originated at the same time as the other major group of
medium-sized grazing ungulates, the artiodactyls (bovids, e.g. cattle) (Schaeffer 1948). All
ungulates utilise symbiotic microorganisms to digest cellulose, either primarily in the rumen
Introduction 8
(foregut fermentation, bovids) or caecum (hindgut fermentation, equids). The highly
efficient ruminant digestion system has been cited as a reason for the spectacular
evolutionary success of bovids compared to equids which employ caecal fermentation (Moir
1968; Schmidt-Nielsen 1997). In the middle-fibre range (medium-quality grasses) (Janis
1976), the concentration of fibre is sufficiently low to allow high digestion co-efficients and
high intakes due to fast passage rates though the rumen (Campling and Lean 1983). This
‘nutrition model’ also predicts that caecal fermenters are more efficient digesters of low-
fibre and high-fibre plant tissues (Demment and Van Soest 1985), and that equids should be
able to extract more from grasses with very high fibre contents because food passes faster
through the hind-gut, which has no selective delaying mechanism (Menard et al. 2002). For
this reason, caecal fermenters are thought to and can eat relatively more than ruminants
(Alexander 1946; Van Soest et al. 1983), but not necessarily and Berman (1991) found no
evidence for feral horses consuming greater herbage biomass than cattle in central Australia.
Recent reviews and evidence from feeding trials with the Camargue horses in stalls and at
pasture (Duncan et al. 1990; Duncan 1992) confirm that feral horses have the potential to
live on coarser forage than bovids because they can ingest more dry forage per kilogram of
body weight per day (i.e. high intake rates). Their intake probably does not decline on coarse
forage because they extract nutrients faster from the lowest quality forage (Bell 1970, 1971;
Janis 1976). However, as horses ate 63% more forage than cattle when fed medium-quality
forage, horses acquire more digestible nutrients per day and likely achieve higher nutrient
extraction rates across a wide range of forage quality (Illius and Gordon 1992; Menard et al.
2002). Higher levels of forage intake have also been associated with longer daily grazing
times in feral horses compared to cattle (Fleurance et al. 2001; Vulink 2001): 50–73%
compared to 32–48% of their time, respectively (Lamoot et al. 2005 and references therein).
The greater invasion of exotic plants in natural grasslands in terms of richness and cover
under feral horse compared to cattle grazing in Argentina was attributed to the above
differences in digestive physiology and ecology, as well as the larger body size and mass of
feral horses making a larger impact on the structure of the vegetation and on the soil surface
(Alejandro et al. 2010). The area covered by feral horse dung in natural grasslands (2.5%)
was also greater than results obtained for cattle elsewhere (0.4–1.0%) (Loydi and Zalba 2009
and references therein).
On the basis of digestive system, metabolic requirements, body size, and comparative
diet studies in desert sagebrush steppe (Hanley and Hanley 1982; Ganskopp and Vavra 1986;
Introduction 9
McInnis and Vavra 1987; Crane et al. 1997a), feral horses are considered to be bulk grazers
and one of the least selective ungulates in western North America (Beever 2003). However,
in more heterogeneous and productive environments, horses feed selectively, switching
preferences seasonally to seek out the greenest food plants and foraging selectively amongst
and within different plant communities and habitats, sometimes producing a heterogeneous
mosaic in vegetation structure of tall and short swards (Duncan 1983; Ganskopp and Vavra
1986; Duncan 1992; Loucougaray et al. 2004). The flexible feeding ecology outlined above
has assisted feral horses to persist under a broad range of ecological conditions (Berger
1986). It follows that the range of environmental impacts due to horses is also broad with
variable outcomes as horses respond to their environment in a heterogeneous fashion
(Turner 1987; Nimmo and Miller 2007)
1.4 Feral horse ecological impact studies and densities
1.4.1 Impact on plant communities
General models of the effect of grazing on plant communities predict that grazing:
(1) increases species richness due to reduction of competitive dominants, especially at
intermediate grazing levels; (2) can stimulate primary production at low and moderate levels
while extreme levels reduce the photosynthetic capacity of vegetation; (3) results in
increases in less palatable or non-preferred species; and (4) facilitates the invasion of exotic
plant species (McNaughton 1979, 1985; Stohlgren et al. 1999; Milchunas 2006). All of these
effects have been documented in the international literature for feral horse grazing and are
summarised in Appendix 1.
1.4.1.1 Europe
Horses were re-introduced as ecological substitutes for wild horses (Bunzel-Drűke
2001) into wetlands in conservation areas in parts of the Camargue in France, and other
European countries (e.g. Lake Pepe, Latvia and Biebrza Marsh, Poland) in order to restore
and enhance plant and bird diversity (Heath et al. 2000; Bokdam et al. 2002; Borkowski
2002). The vegetation had moved towards dominance by a monoculture in the absence of
grazing (Tamisier and Grillas 1994; Schwartz 2005). In an artificial small-scale grazing
experiment in the Camargue wet grasslands, plant species diversity was maximised under
horse grazing and the structural heterogeneity of the vegetation increased (Loucougaray et
al. 2004) (Appendix 1). The authors argued that grazing by horses (and mixed grazing with
Introduction 10
cattle) was an optimal management regime for conservation purposes as the horse-induced
heterogeneity favours many species of waterfowl of international conservation importance,
and wigeon (Anas penelope), an important game species, prefers short swards created by
horses (Vulink et al. 2001).
During the initial 5 years after horses were released into the Camargue, densities
ranged from 0.042 horses/ha to 0.131 horses/ha and the impact on the vegetation was slight
over most of the 300 ha of range (Duncan 1992). The robust response of the vegetation was
not surprising given the long history of grazing, and average biomass increased concurrently
with the horse population due to high rainfall in the first few years, followed by notably drier
years (Vlassis 1978; Duncan 1992). The initial introduction at lower densities had the
desired effect of reducing the cover, height, biomass, frequency and density of the tall,
dominant perennial graminoid species. Once the competitive exclusion by the dominant
species was relaxed, the marshes and grasslands moved towards a more open structure with
a species-rich herb layer.
However, the Camargue herd was not managed and in less than 10 years, the density
peaked at 0.270 horses/ha and all horses were removed due to insufficient food resources.
The dominant, tall perennials were highly preferred by the horses, contributed most to
biomass and were intolerant of heavy, frequent defoliation (Duncan 1992). Some of the
dominant species were almost eliminated under the higher horse densities, and the primary
production of the marshes dropped to less than 20% (Duncan and D'Herbes 1982; Menard et
al. 2002). In the marshes, total species richness did not increase but the biomass of non-
preferred submerged annual plants, virtually absent from the ungrazed plots in exclosures
presumably due to competition with the dense tall reeds, increased under grazing (Duncan
and D'Herbes 1982). Total species richness also increased in the grasslands as the number of
annual grasses and forbs increased in frequency and abundance in grazed plots while
declining in ungrazed plots (Duncan 1992). As predicted by general grazing models, the only
perennial species that maintained themselves or increased under grazing were not important
food species for horses. Duncan (1992) concluded that continual high grazing pressure by an
unmanaged population of horses would in the long term lead to a shift to vegetation
communities with a very low capacity to sustain large mammals. Undesirable impacts of
over-grazing were also recorded at Lake Pepe with a harem group that had no ability to
expand its home range (Prieditis 2002). In the New Forests in the United Kingdom, feral
ponies have also had major impacts on vegetation structure and species composition,
Introduction 11
preventing natural regeneration of the herbaceous groundstorey and shrub and tree layer
over large areas of forest (Mountford and Peterken 2003).
1.4.1.2 The Americas and Australasia
Effects similar to the major impact of feral horse grazing in the Camargue have been
documented in wetland ecosystems on the North American Barrier Islands and in riparian
flush zones in New Zealand (Appendix 1). On the Barrier Islands, feral horses were not
restricted in their range movements, but their activities were concentrated in the salt
marshes (Eline and Keiper 1979; Turner 1987, 1988; Furbish and Albano 1994) (Appendix 1).
On island foredunes, the removal of perennial vegetation led to an increase in the area of
bare sand and a reduction in dune height and topography, contributing to the accelerated
erosion of sand dunes (Seliskar 2003; De Stoppelaire et al. 2004). In New Zealand, flush
zones have been highly modified by a history of feral horse grazing and are now dominated
by adventive grasses with the potential to threaten habitat for rare or regionally significant
plant species (Rogers 1991, 1994).
The impact of feral horses in semi-arid environments on the North American
mainland has been variable in comparison. At sites adjacent to springs, plots grazed by
horses recorded a reduction in vegetation height, cover and total species richness and an
increase in grazing-resistant forbs and exotic species, in comparison to ungrazed plots
(Beever and Brussard 2000a; Beever et al. 2008). Regional horse densities were relatively
low (<0.030 horses/ha; Berger 1986), yet sites closer to water have been shown to incur high
grazing pressure in grazing gradient studies (Landsberg et al. 2003; Hoshimo et al. 2009).
Berman (1991) also found that the environmental impacts of horses in central Australia, such
as the removal of herbaceous ground cover, diminished as distance from permanent water
increased (Appendix 1).
In exclosure studies not necesarily close to watering points, significant effects of
horse exclusion were found only for biomass and percent cover of one or two dominant
graminoid species preferred by horses (Fahnestock 1998; Fahnestock and Detling 1999a,
1999b). The authors suggested that horse densities or length of exclusion time were
sufficiently low to prevent major changes in grassland vegetation (Detling 1998). Changes in
cover and plant species composition were typically determined more by inter-annual
differences in rainfall (above average wet versus dry years) or by site variation than grazing
(Fahnestock 1998; Fahnestock and Detling 1999b) (Appendix 1). A modern history of
Introduction 12
continual grazing at relatively low regional densities (0.011–0.020 horses/ha, Appendix 1)
probably contributed to the ability of the dominant graminoids to withstand frequent
defoliation via morphological adaptations that led to compensatory growth (Fahnestock and
Detling 1999a, 2000).
1.4.2 Impact on soil surface properties, tracks and weed dispersal
Beever and Herrick (2006) found 3.0–15.4 times lower penetration resistance in
surface soils and 2.2–8.4 times greater abundance of ant mounds at horse-removed sites
compared to horse-occupied sites, with the range in differences explained by elevation.
Other studies have concentrated on feral horse tracks, which are typically linear pathways of
bare, compacted soil created by repeated trampling and prone to erosion (Jarman et al.
2003; Ostermann-Kelm et al. 2009). In Australian environments, track networks can be quite
extensive, ranging from 3.4–5.8 km of track per km2 in the Alps (Dyring 1990; Andreoni
1998). Plant species richness has been found to decline on tracks and the soil disturbance
caused by trampling and removal of vegetation can create conditions that aid in the dispersal
of exotic species, as does horse dung (Dyring 1990; Taylor 1995; Campbell and Gibson 2001).
In the Americas, while dung, assisted by gap creation and soil disturbance, may facilitate the
invasion of exotic species, dung piles may also provide a refuge from grazing for some grazing
sensitive species (Loydi and Zalba 2009; Alejandro et al. 2010). At intermediate levels of
disturbance native plant richness has also been found to be greater near tracks and dung
piles (Ostermann-Kelm et al. 2009).
1.4.3 Indirect impact on wildlife species and faunal communities
Across Europe, the effect of re-introducing horses on bird communities has been
variable: some species increased and others declined, depending on their ecological niche
and requirements for breeding and predator avoidance (Duncan and D'Herbes 1982; Duncan
1992; Bokdam et al. 2002). In South America, Zalba and Cozzani (2004) found higher avian
richness and diversity in areas under moderate or intermediate levels of grazing than areas in
which horses had been excluded. In areas of high intensity grazing, however, habitats were
less diverse and the rate of egg predation increased, leading to a reduction in the richness
and density of birds. On one of the North American Barrier Islands, bird richness increased
but the feral-horse-induced changes in vegetation structure altered bird communities in the
marshes and reduced the value of the marshes as nursery grounds for fishes and decapods
Introduction 13
(Levin et al. 2002) (Appendix 1). On the North American mainland, increased soil-surface
hardness affected small mammal assemblages, in particular fossorial species, with an
increase in those species insensitive to disturbance (Beever and Brussard 2004). Small reptile
diversity and abundance also declined. In terms of competition with native grazing
ungulates, feral horses may act as a competitor or facilitator (Berger 1985, 1986). Male
desert bighorn sheep (Ovis canadensis) forage greater distances from predator-avoidance
escape terrain when foraging with horses as opposed to conspecifics, and their foraging
efficiency increases as less time is spent on intraspecific aggression and social interactions
(Coates and Schemnitz 1994). Evidence of facilitation was not found in the same population
of horses and desert bighorn sheep when predator density was high, and as a result sheep
numbers declined. Rather, desert bighorn sheep changed their diet to minimise overlap with
horses (Kissell 1996 and pers. comm.). In Australia, several species of macropods, such as the
euro (Macropus robustus) and red kangaroo (Macropus rufus) have appeared to prosper in
conjunction with livestock grazing (Newsome 1975). The beneficial relationship between
kangaroos and cattle is based on cattle removing the dry, mature perennial pasture layer and
promoting nutritious new, green re-growth, which only kangaroos can graze based on
differences in tooth morphology (Frith 1970; Janis 1990). The foraging relationship between
horses and macropods is unknown, although exploitative (resource) competition has been
hypothesised (Olsen and Low 2006).
1.4.4 Summary
In conclusion, the preceding pages noted:
(1) the requirement for environmental impact studies in GFRNP and Australia
(2) the impact of feral horses and ungulate grazers on: (i) preferred perennial plants in
productive areas or where resources are limited; (ii) composition of plant
communities and plant richness indices; (iii) vegetation structure and ecosystem
productivity and biomass; (iv) condition of surface soils, such as loss of plant cover,
soil compaction, erosion and soil loss; (v) the ratio of native to exotic plant species as
horse dung can be an agent for dispersal of viable seeds and provide nutrients and
protection from climatic conditions and grazing herbivores; (vi) and native wildlife.
The aforementioned impacts have not been extensively examined in temperate–
subtropical ecosystems for feral horses in Australia and in addition to the requirement for
ecological impact studies in GFRNP, will be addressed in this thesis. Several reviews (Beever
Introduction 14
2003; Beever et al. 2003; Nimmo and Miller 2007; Abella 2008) highlighted knowledge gaps
in the understanding of the ecological effects of feral horses on native ecosystems which this
thesis also aims to address, such as:
(1) the uncertainty about the effect of feral horses at broader scales, for example: (i) at
the landscape scale where impact may vary according to factors such as topographic
position in the landscape (e.g. hillslope or spur), slope, aspect, elevation and habitat
type; (ii) on feed-back mechanisms between structural changes, such as a reduction
in ground cover and compaction of the soil surface, and aspects of landscape
function, such as soil surface stability, nutrient recycling, and water infiltration; and
(iii) indirect effects on medium sized herbivores (macropods) that occupy a similar
feeding niche as feral horses and the different effect horses may have from native
herbivores in regulating ecosystem processes, such as biomass accumulation, plant
species richness, and persistence of dominant tussocks via reproductive adaptations.
1.5 Thesis outline
The background to this thesis and purpose were briefly mentioned in the previous
section. In response to the limitations of previous feral horse impact studies, experiments
were conducted at a range of scales in several habitat types, utilising a broad set of response
variables, and the results were interpreted in terms of feedback loops between the direct
and indirect effects of feral horses. The objectives of this thesis as they relate to each
chapter are:
Chapter 2: to provide a context for experimental chapters by describing the environment
and climate of the general study area, GFRNP, and how levels of past and current feral
horse and cattle activity determined which parts of GFRNP were selected for a landscape-
scale comparison of horse and non-horse management zones or catchments
Chapter 3: to monitor dung counts of horses and macropods in conjunction with
reductions in feral horse numbers to test the relationship between horses and small-
scale habitat use and selection of foraging sites by macropods. In addition, the results of
dung counts showed the relative distribution of macropods in catchments with and
without horses
Chapter 4: to use exclosures on a high-elevation plateau to evaluate the response of the
groundstorey vegetation in open, grassy eucalypt woodlands associated with drainage
swales to horse grazing and trampling. The exclosure design enabled the effects of
Introduction 15
horses and native herbivores on the following variables to be compared: biomass, cover
and plant species richness indices, reproductive output of the dominant, perennial
tussock grass, and vegetation structure and composition
Chapter 5: to repeat the exclosure experiment on the most highly preferred landscape
unit, grassy riparian flats in a high-use gorge country in GFRNP
Chapter 6: to examine the effect of horses on the structural and functional integrity of
the dominant broad scale landscape units, hillslopes and spurs, in gorge country in
GFRNP heavily used by horses, with particular reference to horse tracks
Chapter 7: present a synthesis of the findings and conclusions, including implications for
management if horses were to remain or be eliminated from the Park, and further
research.
CHAPTER 2.
STUDY AREA
2.1 Introduction
The study area was in Guy Fawkes River National Park (GFRNP, or the Park) in north-
eastern New South Wales (NSW) (Figure 2.1a) and administered by the Dorrigo Plateau Area
Chapter 2. Study Area 16
office of the NSW National Parks and Wildlife Service (NPWS). The Park is on the eastern
edge of the New England Tablelands region of the Northern Tablelands Statistical Subdivision
of NSW, approximately 80 km and 40 km north-east of Armidale and Guyra and adjacent to
Ebor (Figure 2.1b). When established in 1972, the Park was 25 400 ha but now encompasses
100 600 ha, of which an area of 83000 ha was declared wilderness in 1994 under the
Wilderness Act, 1987 (NSW NPWS 2009b). The landscape is characterised by steep, narrow,
rocky gorges with narrow river flats along the bottom of the gorges. The Great Dividing
Range in eastern Australia was formed 80 to 90 million years ago and the ensuing erosion,
assisted by numerous river systems, marked the beginnings of the deeply incised and rugged
gorge country (McInherny and Schaeffer 2004b). Major river gorge systems include the Sara
River in the north (flowing east), the Aberfoyle River in the south (flows north-east), and the
Guy Fawkes River (GFR), which extends the length of the Park (flows north). The Aberfoyle
and Sara flow in to the Guy Fawkes River, which drains to the Boyd River in the northern tip
of the Park (Reid et al. 1996). Elevation varies from 200–300 m along the river flats to
1378 m at Chaelundi Mountain on the south-eastern boundary; most of the Park is remote
and has slopes between 10° and 30° (Reid et al. 1996). Over 40 vegetation communities have
been mapped containing 5% of Australia’s flora (Reid et al. 1996; Austeco 1999). The
vegetation of the higher elevation plateaus (1000 m) and slopes is mostly a mixture of
semi-mesic to dry sclerophyll forest communities with an open grassy understorey
(Henderson and Keith 2002). Climate follows a subtle gradient from subtropical at the
northern end of the Park (mean annual temperature >18°) to temperate on the tableland
plateaus and ridges above 800 m towards the southern and eastern borders (mean annual
temperature <15°) (Reid et al. 1996). Like temperature, rainfall varies with elevation from
800 mm in the river gorges to more than 1400 mm on elevated ridges and higher points on
the plateaus with a summer maximum and late winter–early spring minimum. At higher
elevations, frost appears at the beginning of March and is intermittent until November with
occasional snowfalls in winter (McInherny and Schaeffer 2004b).
Chapter 2. Study Area 17
Figure 2.1 a) Guy Fawkes River National Park (The Planning Area) within Australia (Google Maps) and b) regional locality map reproduced from NSW NPWS (2009b).
Chapter 2. Study Area 18
The Park is divided into 14 catchments based on the major river gorge systems and
their tributaries, also termed management zones (MZs; Table 2.1). Several catchments were
named after the tributaries that run through them, for example, Bobs Creek and Sara River.
To avoid confusion and repetition, and since this chapter describes the management history
of the Park, the term management zone will be used primarily and abbreviated to MZ when
referring to the catchment area, for example, Bobs Creek MZ and Sara River MZ. No
additional notation was used when referring to the tributary, for example, Bobs Creek and
Sara River. The term catchment will be used in all other chapters because of their ecological
context. The major rivers were identified previously; all other tributaries are creeks that flow
into one of those major rivers. Manipulative experiments involving exclosures were
conducted in two catchments, Bobs Creek and Paddys Land Plateau (Paddys Plateau
hereafter), and a landscape-scale survey conducted in Bobs Creek and three other
catchments, Pargo Creek, Kangaroo Creek and Pantons Creek. The objective of this chapter
was to describe the management history of each catchment with a focus on the length and
intensity of feral horse and cattle occupation. Cattle were a potential confounding factor
while horse densities provided the context for interpreting any ecological impacts of horses
detected. The selection of catchments for the landscape-scale survey in Chapter 6 is
summarised in Section 2.6.
Chapter 2. Study Area 19
Table 2.1 Areas of the Park that have been assigned a management zone (MZ) name and code by the NPWS Dorrigo Plateau Area office, accompanied by date acquired or gazetted, size and proportion of Park area of each MZ. Information provided by Brad Nesbitt or extracted from the relevant GIS shapefile and attribute table.
MZ code Management zone (MZ)
Date acquired Size (ha)
Area of the Park (%)
1 Pantons Creek–northern half 1995 760 3.2
Pantons Creek–southern half 2001 894 2 Upper Guy Fawkes River 1972 4857 9.4 3 Marengo 1972 2644 5.0 4 Aberfoyle River–western half 1999 1294
7.2 Aberfoyle River–eastern half 1972 2475
5 Combolo 1972 2524 4.8 6 Mid Guy Fawkes River 1972 4159 8.0 7 Kittys Creek 1972 3685 7.0 8 Paddys Land Plateau–western half 1997 3205
11.8 Paddys Land Plateau–north-eastern half 1999 3032 from Dingo Spur into Boban Tops/Hut
9 Bobs Creek–northern half 1972 1111 6.0
Bobs Creek–southern half 2000 2022 10 Pargo Creek 2000 2081 4.0 11 Sara River 1972 4826 9.3 12 Lower Guy Fawkes River 1972 4149 8.0 13 Glen Nevis Plateau 1997 4369 8.3 14 Kangaroo Creek 1972 4257 8.1
In Sections 2.1–2.3, ‘stock-horse’ implies ownership and refers to domestic horses
bred in captivity and released to run wild with the intent to recapture or muster the majority
of these for the lucrative remount export trade (1840s to 1940s). ‘Brumby’ refers mostly to
remnant populations of stock-horses after the 1940s when the remount trade had dried up
and large numbers of stock-horses were no longer turned loose with the purpose of breeding
up populations. Breeding between brumbies and stock-horses occurred but was not
targeted and generally occurred as a result of lack of fencing or escaped horses. ‘Feral horse’
or horse refers to the period after 1972 and the gazettal of the Park.
Several maps are presented in the following sections, and were created in a
Geographical Information System (GIS), ArcGIS v 9.1 (ESRI 2005). The Department of
Environment, Climate Change and Water (DECCW) GIS support officers, Lyn McRae and Annie
Blaxland, supplied numerous geographical and environmental data layers in addition to the
Global Positioning System (GPS) co-ordinates (text file format) for horse and cattle sightings.
For vector features (points, lines and polygons) (e.g. MZ polygon outlines, river polylines)
data sources were ESRI Shapefiles. Raster-based datasets were mostly ERSI Grid format (e.g.
Chapter 2. Study Area 20
digital elevation models, slope, rainfall) with a resolution of 1 ha (100 × 100-m grid cells).
The exception was topographic map layers, which were MrSID format (Multi-resolution
Seamless Image Database), a powerful image compressor, viewer and file format for massive
raster images. Data layers were accompanied by dBase tables (attribute tables) that
contained additional descriptive information (e.g. number of feral horses in a mob
corresponding to a single GPS point) used to create summary tables. Additional information
in hard copy (e.g. cattle infringement notices, letters of complaint) or verbal clarification was
provided by the Senior Ranger-in-Charge of GFRNP, Tony Prior, and the Pest Species
Management Officer, Brad Nesbitt, Dorrigo Plateau Area, NSW NPWS. Several long-term
resident graziers with property adjacent to the MZs of interest, and those descendents of the
early settlement families (e.g. Brian Fahey) were also consulted, as were horsemen
(e.g. Graham Baldwin, David O’Brien) involved with the horse musters as part of control in
the 1990s.
2.2 White settlement and early grazing history
Until the Park was gazetted in 1972, the area was inhabited and managed by graziers
for sheep and cattle grazing (Table 2.2, Figure 2.3). The first cattle station ‘run’ on the
Dorrigo Plateau was Guy Fawkes Station (GFS) established in the late 1830s by Major Parke;
it remains in operation today (Heritage Working Party 2002a). All original runs and station
properties including GFS have since been sub-divided. GFS increased in the 1880s and would
have included at least the southern tip of Pantons Creek MZ (Table 2.2) (Waugh 1971).
Kangaroo Creek MZ is located to the east and runs parallel to Pantons Creek MZ with pastoral
subdivisions corresponding to Dyamberin Station separating the two MZs. The Kangaroo
Hills Run was established in 1842 and in 1908 was divided into Wongwibinda (4900 ha) and
Dyamberin (6100 ha) Stations (Rampbeck Run) (MacDougall 2001). The first station
protruded into the southern tip of Kangaroo Creek MZ and the second encompassed the
eastern section of Kangaroo Creek and the western section of Pantons Creek MZs
(Figure 2.3). Sheep were grazed early on, for example, at stocking densities of
0.390 sheep/ha in 1844 at Kangaroo Hills (Table 2.2), with cattle now prominent. Parts of
Pantons Creek and Kangaroo Creek MZs were thus grazed to variable extents by sheep and
cattle for up to 161 years and 130 years respectively, as Pantons Creek was acquired for the
Park from 1995–2001 and Kangaroo Creek in June 1972.
Chapter 2. Study Area 21
At the same time as GFS was established, the Aberfoil Run was set up, and was
almost four times the size of GFS with stock numbers doubling from 1840 to 1844 (Table 2.2)
(McInherny and Schaeffer 2004b). Aberfoil was the original spelling for the name of this run,
and has been used in this thesis as it appeared in historical sources (e.g. published lease
details). The present day spelling of Aberfoyle was well established from about 1885
(McInherny and Schaeffer 2004a). From 1877 to 1883, at least fifty-three leases were taken
out on Aberfoil by early ‘free selectors’ (McInherny and Schaeffer 2004b). The Aberfoil Run
largely corresponded to the eastern portion of the Aberfoyle River and northern section of
Kangaroo Creek MZs, with a grazing history similar in length and intensity as Pantons and
Kangaroo Creek MZs (Table 2.2, Figure 2.2).
North-east of the Aberfoil Run and forming the northern boundary with the
Rampsbeck Run and Kangaroo Hills Run was an area settled in the 1880s and referred to as
Paddys Land (NSW NPWS 2009b) (Figure 2.2). The Newby family ran up to several thousand
head of cattle on Paddys Land in those early years (Fahey 1976). The station incorporated
the present day Paddys Plateau MZ and extended to the north and the east to include the
river flats on the western bank of the GFR into Kittys Creek MZ adjacent to Bobs Creek MZ.
Map of pastoral holdings up until the late 1990s indicated that the gorge sections of Bobs
and Pargo Creek MZs were never allocated to pastoral holdings (Heritage Working Party
2002a). This suggests that they were considered unsuitable for grazing due to the
topography and hence had a history of relatively minor cattle grazing (Heritage Working
Party 2002a). Stock-horses (and later brumbies and feral horses) from the neighbouring
Mt Mitchell (Henry River) and Paddys Land Run may have traversed that country, however,
as horses utilise a wide range of slopes, whereas cattle have a strong preference for flat or
gently undulating ground (Ganskopp and Vavra 1987; Chapters 1 and 6). Conversely, Paddys
Plateau MZ is flat relative to the greater area of the Park and appeared to be attractive to
early settlers given the number of dwellings it contained. Tallagandra Hut was occupied by
graziers until it was acquired by NPWS and is presently used as a field station and equipment
depot. Two Mile Hut, Braziers Hut, Wonga Hut and Boban Hut are either ruins or have
disappeared (Figure 2.2). Adjoining Paddys Land to the west was Wards Mistake, established
earlier in 1842 and may have included parts of Paddys Land in the beginning (Figure 2.2). The
large numbers of stock for the small areas (e.g. 800 ha) in the 1950s and 1970s (Table 2.2)
corresponded to the introduction of superphosphate fertiliser and sown pastures, as Wards
Mistake did not include the gorge country and had been extensively cleared and fenced.
Chapter 2. Study Area 22
Travelling Stock Routes (TSR’s), strips of public land set aside for the droving of stock,
were and are, still present in the Park. The major TSR follows the GFR in traversing the Park
in mostly a north–south orientation and is part of the Bicentennial National Track (BNT)
(Heritage Working Party 2002a). It was gazetted between 1880 (most northerly section) and
1900 (most southerly section), and the later date included a 6-km extension along
Macdonald’s Ridge from Combolo Hut on the banks of the GFR to Marengo Station (Boyd
1991). In 1922, the Combolo TSR was connected to the southern junction of the Sara River
and GFR by a second TSR. A third TSR joins it from Paddys Land in the west of the Park.
These routes are still used to move cattle illegally into the valley of the GFR from Newton
Boyd in the north, then along the GFR and up Macdonald’s Ridge into the only substantial
area of gently undulating land in the area known as the Fattening Paddock via Marengo flats
(Boyd 1991; Reid et al. 1996).
Chapter 2. Study Area 23
Figure 2.2 Location of the early settlement runs and stations relative to each other (McInherny and Schaeffer 2004b). Reproduced with the permission of the Guyra and District Historical Society. WAWM, Wongwibinda, Aberfoyle and Wards Mistake.
Chap
ter
2. S
tudy
Are
a 2
4
Tabl
e 2.
2 A
sel
ectio
n of
the
maj
or s
tatio
ns a
nd r
uns
that
wer
e ei
ther
adj
acen
t to
or
beca
me
part
of
the
Park
in t
he e
arly
whi
te s
ettle
men
t er
a.
Size
and
sto
ck d
etai
ls f
or t
he m
id-w
est
and
sout
h-w
est
regi
ons
wer
e ob
tain
ed f
rom
McI
nher
ny a
nd S
chae
ffer
(20
04b)
and
for
GFS
fro
m F
ahey
(1
976)
. Th
e br
ief d
escr
iptio
n of
the
rem
aini
ng r
uns
and
stat
ions
was
obt
aine
d fr
om M
acD
ouga
ll (2
001)
. G
FR: G
uy F
awke
s Ri
ver.
Run
or S
tati
on
Year
se
ttle
d Lo
cati
on
Size
(ha)
St
ock
deta
ils
Stoc
king
de
nsit
y
Sout
h-ea
st r
egio
n
Guy
Faw
kes
Stat
ion
(GFS
) la
te 1
830s
Pa
nton
s Cr
eek
MZ
10 3
60
1,30
0 ca
ttle
0.
125
catt
le/h
a la
te 1
890s
16
190
Co
ntra
cted
to b
reed
hor
ses
for
Indi
an A
rmy
Litt
le G
uy F
awke
s St
atio
n la
te 1
830s
O
n th
e si
te o
f Ebo
r to
wns
hip
Cont
ract
ed to
bre
ed h
orse
s fo
r In
dian
Arm
y H
erna
ni S
tatio
n 18
40s
Adj
acen
t to
Mar
engo
and
Pan
tons
Cre
ek M
Zs
Catt
le a
nd h
orse
s Ba
ld H
ills
1850
s A
djac
ent t
o Ka
ngar
oo C
reek
MZ
Shee
p M
id-e
ast
regi
on
Mar
engo
Sta
tion
earl
y 18
50s
Mar
engo
MZ
and
Chae
lund
i Sta
te F
ores
t Ca
ttle
and
hor
ses
Com
bolo
Sta
tion
1880
–188
4 Co
mbo
lo a
rea
MZ
Catt
le a
nd h
orse
s Ko
tupn
a Pr
oper
ty
1930
s A
djac
ent t
o M
id G
uy F
awke
s Ri
ver
MZ
Turn
ball
fam
ily b
red
hors
es fo
r In
dian
Arm
y N
orth
-eas
t re
gion
Br
oadm
eado
ws
Stat
ion
1849
Ki
ttys
Cre
ek M
Z, L
ower
and
Mid
GFR
MZs
Ca
ttle
and
larg
e nu
mbe
r of
hor
ses
Nor
th-w
est
regi
on
Mt M
itche
ll Ru
n 18
85
Adj
acen
t to
Parg
o Cr
eek
and
Sara
Riv
er M
Zs
Catt
le a
nd h
orse
s
Mid
-wes
t re
gion
War
ds M
ista
ke S
tatio
n 18
42
Adj
acen
t to
Padd
ys P
late
au M
Z an
d 23
070
2,
000
catt
le
0.08
7 ca
ttle
/ha
and
Run
the
Abe
rfoi
l Run
12
950
In
188
3: 3
,000
cat
tle, 3
0 ho
rses
, 50
shee
p 0.
232
catt
le/h
a 81
0 In
195
0s: 1
2,00
0 sh
eep
810
In 1
970s
: 2,5
00 c
attle
Pa
ddys
Lan
d Ru
n 18
83
Padd
ys P
late
au M
Z U
p to
200
0 he
ad o
f cat
tle
Chap
ter
2. S
tudy
Are
a 2
5
Tabl
e 2.
2 c
onti
nued
. G
FS: G
uy F
awke
s St
atio
n.
Run
or S
tati
on
Year
se
ttle
d Lo
cati
on
Size
(h
a)
Stoc
k de
tails
St
ocki
ng d
ensi
ty
Sout
h-w
est
regi
on
The
Kang
aroo
Hill
s Ru
n 18
42
Kang
aroo
Cre
ek a
nd P
anto
ns C
reek
MZs
14
510
In
184
4: 6
60 c
attle
, 6 h
orse
s, 5
,600
she
ep
0.38
6 sh
eep/
ha
(sub
-div
ided
from
GFS
) In
185
5: 1
3,80
0 sh
eep
Won
gwib
inda
Sta
tion
1908
Su
b-di
vide
d fr
om K
anga
roo
Hill
s
4860
Ca
rryi
ng c
apac
ity o
f 0.5
0 sh
eep/
ha o
r 0.
11 c
attle
/ha
The
Ram
psbe
ck R
un
1867
In
bet
wee
n Ka
ngar
oo H
ills
and
Abe
rfoi
l Run
s 57
00
Carr
ying
cap
acity
of 0
.14
catt
le/h
a
The
Alfr
eda
Run
1865
A
djac
ent t
o Ka
ngar
oo H
ills
and
Ebor
65
0 20
0 ca
ttle
0.
301
catt
le/h
a
12 1
40
In 1
885:
28
catt
le, 6
hor
ses,
3,5
50 s
heep
0.
292
shee
p/ha
Abe
rfoi
l Run
18
39
Exte
nded
into
Abe
rfoy
le R
iver
MZ
and
38 0
80
In 1
840:
450
cat
tle, 3
hor
ses,
6,1
27 s
heep
0.
161
shee
p/ha
Kang
aroo
Cre
ek M
Z, a
djac
ent
to
In 1
844:
1,0
30 c
attle
, 29
hors
es, 1
0,92
6 sh
eep
0.28
7 sh
eep/
ha
Padd
ys P
late
au M
Z 45
130
In
187
6: 8
,000
cat
tle
0.17
7 ca
ttle
/ha
Chapter 2. Study Area 26
Figure 2.3 Location of the early pastoral settlement stations and runs in relation to present day management zones (MZs). TSR: Travelling Stock Route, GFS: Guy Fawkes Station, LGFR: Little Guy Fawkes Station. The number bolded in black in the centre of each MZs outline corresponds to the MZ Code in Table 2.1. 1: Pantons Creek, 2: Upper GFR, 3: Marengo, 4: Aberfoyle River, 5: Combolo, 6: Mid GFR, 7: Kittys Creek, 8: Paddys Plateau, 9: Bobs Creek, 10: Pargo Creek, 11: Sara River, 12: Lower GFR, 13: Glen Nevis Plateau, 14: Kangaroo Creek.
Chapter 2. Study Area 27
2.3 Feral horse history prior to Park gazettal
The MZs in the central-northern section of the Park had a similar history of
settlement and grazing as those in Section 2.2 (MacDougall 2001). The main difference was
that the Gulf Country, a term used to describe the dissected gorge country created by the
rivers and creeks in the region including the Guy Fawkes, Aberfoyle, Sara, Oban, and Henry
Rivers and the Bobs, Pargo, and Kittys Creeks (Figure 2.4) was not continually used by cattle
and sheep graziers (Heritage Working Party 2002a). Rather, the area was utilised over winter
because the gorges were always greener with higher quality feed (Fahey 1976). However,
the Gulf Country and the stations and runs in the central-north were associated more with
brumbies than the south in the mid 1900s (Table 2.3).
Written accounts of stock-horses did not appear until after 1920, but as early as
1871, a reward was offered for the capture of people responsible for the shooting of stock-
horses by William Coventry of Aberfoil in the Armidale Express (McInherny and Schaeffer
2004b). Stock-horses were in residence at GFS and Little Guy Fawkes Station (LGFS) from the
beginning, and an extensive herd was soon bred up and, without fencing, were free to roam
over thousands of acres (Fahey 1976). The early squatters largely followed Major Parke’s
example at GFS (e.g. Dyamberin Station, Bostobrick Station; Table 2.3). Up until the 1940s,
horse breeding for the overseas remount trade was a lucrative business, with the British
Army in India a major client (Fahey 1976; MacDougall 2001). Horses were bred from former
stock mares and turned out to run free in their hundreds (Heritage Working Party 2002a).
Mobs were run in or mustered on horse-back and depending on their quality and suitability,
many or just a few, were broken and sold in large consignments (e.g. 250 stock-horses from
Aboomala Station in the 1930s, Table 2.3). This tradition of mustering large mobs was
romanticised in Banjo Patternson’s The Man from Snowy River. The following also occurred
and became the common practice after the remount trade was no longer economic. Mobs
were mustered into make-shift yards (e.g. seven brumbies at Peaks Creek, 1933; Table 2.3)
and the best of the young brumbies were kept for local domestic stock horses, and the rest
shot to keep numbers down and reduce competition with cattle (Heritage Working Party
2002b). Rather than mustering mobs into yards, one or two were targeted for stock and
station work and ‘roped’, with injured or poor quality animals shot in the process.
Colloquially termed ‘brumby running’, this practice peaked during 1939–1945 when training
camps for the 12th Light Horse Brigade in the New England District required each solider to
provide his own horse and continued up until areas were gazetted as Park (Heritage Working
Chapter 2. Study Area 28
Party 2002a). Oral histories suggest that brumby numbers were always controlled prior to
World War II and started to build up in numbers after 1965 due to the lack of experienced
stockman and economic markets, boosted the technologies (e.g. sown and fertilised
pastures) that accompanied generational change, which made the ‘working horse’ redundant
(Heritage Working Party 2002b).
Chap
ter
2. S
tudy
Are
a 2
9
Tabl
e 2.
3 F
irst-
hand
acc
ount
s an
d or
al h
isto
ries
of
brum
by s
ight
ings
fro
m t
he 1
920s
to
whe
n ar
eas
first
bec
ame
Park
. Lo
catio
ns c
orre
spon
d to
‘k
ey lo
catio
ns’ i
n Fi
gure
2.4
. Pa
ge n
o. c
orre
spon
ds to
whe
re in
form
atio
n w
as o
btai
ned
in H
erita
ge W
orki
ng P
arty
(200
2b) a
nd M
acD
ouga
ll (2
001)
. Th
e in
form
atio
n is
sum
mar
ised
pic
tori
ally
in F
igur
e 2.
4 us
ing
a co
lour
cod
ed s
yste
m to
rep
rese
nt a
ppro
xim
ate
hist
orie
s an
d br
umby
num
bers
.
Loca
tion
Ye
ar
Obs
erva
tion
/com
men
t So
urce
Pa
ge
no.
Nor
ther
n re
gion
Day
s W
ater
nea
r Sa
ra R
iver
the
n so
uth
to
mid
193
0s
Form
er s
tock
mar
es tu
rned
out
to r
un fr
ee a
nd
Gen
evie
ve
New
bury
36
A
berf
oyle
Riv
er–M
itch
ell R
un w
est o
f Par
k be
com
e br
umbi
es
Corn
er C
amp,
upp
er (w
est)
Sar
a Ri
ver
nort
h
1940
s Br
umby
run
ning
occ
ured
, app
roxi
mat
ely
50 b
rum
bies
Er
nie
Mas
key
22
to H
enry
Riv
er
Broa
dmea
dow
s St
atio
n an
d ru
n 19
00–1
960s
Po
pula
tion
kept
und
er c
ontr
ol b
y pe
riod
ic m
uste
rs a
nd
Tiny
Hum
e co
ntra
ct s
hoot
ing
to r
educ
e co
mpe
titio
n w
ith c
attle
M
id n
orth
-eas
t re
gion
Co
mbo
lo F
lat
19
28
Brum
bies
sig
hted
and
sto
ck h
orse
s ra
n of
f with
a
Joe
Mee
han
24
mob
aft
er g
ate
left
ope
n Ki
ttys
Cre
ek ju
nctio
n w
ith G
FR
1930
s Br
umbi
es tr
appe
d an
d he
ld in
Litt
le P
lain
s Ya
rd
Dou
g M
eyer
36
M
aren
go S
tatio
n, s
tret
ch o
f GFR
bet
wee
n
1931
–32
Seve
ral b
rum
by m
uste
rs b
y fo
ur d
iffer
ent
stoc
kman
, tow
ards
N
oel M
acD
ouga
ll 23
Pe
ak C
reek
and
Litt
le P
lain
are
a en
d of
193
2 tr
ap y
ard
setu
p an
d br
ough
t gre
ater
suc
cess
Pe
ak C
reek
19
33
7 Br
umbi
es c
aptu
red
in tr
ap y
ard—
thou
ght t
o be
the
N
oel M
acD
ouga
ll 23
la
st o
f the
Bro
wn
fam
ily b
rum
bies
Ki
ttys
Cre
ek
1933
Re
calle
d no
bru
mbi
es a
t tha
t tim
e N
oel M
acD
ouga
ll 23
G
FR fl
ats
from
Mid
Guy
Faw
kes
Rive
r M
Z 19
35–3
6 Re
calle
d fe
w b
rum
bies
at t
hat t
ime
Jam
es H
icke
y 24
to
Mar
engo
MZ
Flet
cher
Bra
zier
19
45–4
6 5–
6 H
orse
s si
ghte
d al
ong
the
GFR
bet
wee
n Bo
yd R
iver
N
oel M
acD
ouga
ll 35
an
d Ki
ttys
Cre
ek
Com
bolo
and
Hou
sew
ater
Cre
ek a
rea
Late
194
0s
Reca
lled
no b
rum
bies
at t
hat t
ime
Noe
l Mac
Dou
gall
23
Litt
le P
lain
are
a, ju
nctio
n of
Lon
g G
ap C
reek
19
45–4
6 17
Bru
mbi
es s
ight
ed
Noe
l Mac
Dou
gall
23
Chap
ter
2. S
tudy
Are
a 3
0
Tabl
e 2.
3 co
ntin
ued.
Loca
tion
Ye
ar
Obs
erva
tion
/com
men
t So
urce
Pa
ge n
o.
Mid
nor
th-e
ast
regi
on c
onti
nued
Ki
ttys
Cre
ek a
nd C
ombo
lo a
rea
1970
A
roun
d 50
bru
mbi
es s
ight
ed, s
ugge
sted
that
bru
mbi
es
Erni
e M
aske
y 22
fr
om H
enry
Riv
er/C
orne
r Ca
mp
had
and
wer
e m
ovin
g do
wn
on
to th
e Sa
ra R
iver
and
late
r in
to K
ittys
Cre
ek/C
ombo
lo
Hou
sew
ater
Cre
ek a
rea
1970
s A
few
bru
mbi
es s
ight
ed
Terr
y Br
azie
r 24
W
ongw
ibin
da to
Litt
le P
lain
on
the
GFR
19
85
Whi
lst r
idin
g co
unte
d 26
8 br
umbi
es, m
ostly
from
D
oug
Ferr
is
25
GFR
–Pan
tons
Cre
ek Ju
nctio
n no
rth
to L
ittle
Pla
in a
rea
Litt
le P
lain
, 3 k
m u
pstr
eam
from
19
93
Erni
e M
aske
y le
d br
umby
mus
ter
and
in 1
0 ru
ns
Erni
e M
aske
y 22
Sa
ra R
iver
–GFR
Junc
tion
capt
ured
54
brum
bies
M
id n
orth
-wes
t re
gion
Abo
omal
a H
omes
tead
, 6.5
km
eas
t of G
uyra
19
30s
Brum
by m
uste
r w
ith 2
50 b
rum
bies
from
G
enev
ieve
N
ewbu
ry
21
Padd
ys L
and
sold
or
brok
en
Mor
ning
ton
Stat
ion
to B
oban
Top
s/H
ut a
rea
1930
s Pr
oper
ty o
wne
rs p
aid
on a
per
-hea
d ba
sis
Le
s H
ume
22
for
brum
bies
sho
t as
a m
eans
of c
ontr
ol
Parg
o an
d Bo
bs C
reek
MZs
19
40–1
970
Reca
lls a
lway
s br
umbi
es in
that
are
a, m
axim
um o
f 50
hors
es
Erni
e M
aske
y 36
Bo
bs C
reek
, Com
bolo
and
Bob
an T
ops/
Hut
19
44–4
6 Re
calle
d ri
ding
in th
e ar
ea a
nd s
eein
g go
od q
ualit
y ho
rses
Ja
ck G
iles
24
Balla
rds
Flat
on
Sara
Riv
er, a
djac
ent t
o
mid
194
0s
Dou
g M
eyer
and
two
othe
rs r
ecal
l run
ning
bru
mbi
es h
ere
Dou
g M
eyer
36
Bo
bs a
nd P
argo
Cre
ek M
Z M
orni
ngto
n St
atio
n to
Bob
an T
ops/
Hut
are
a 19
45–1
965
Mrs
New
bury
had
mob
s of
bru
mbi
es a
nd
Flet
cher
Bra
zier
24
w
ould
not
allo
w th
em to
be
shot
unt
il dr
ough
t of 1
965
Chap
ter
2. S
tudy
Are
a 3
1
Tabl
e 2.
3 co
ntin
ued.
Loca
tion
Ye
ar
Obs
erva
tion
/com
men
t So
urce
Pa
ge n
o.
Mid
nor
th-w
est
regi
on c
onti
nued
M
t Won
ga F
lat o
n Pa
ddys
Pla
teau
MZ
1957
20
Bru
mbi
es s
ight
ed
Flet
cher
Bra
zier
24
Pa
rgo
Flat
, abo
ve P
argo
Cre
ek M
Z an
d
1959
17
Bru
mbi
es s
ight
ed
Flet
cher
Bra
zier
36
ad
jace
nt to
Pad
dys
Plat
eau
MZ
Mor
ning
ton
Stat
ion
to B
oban
Top
s/H
ut a
rea
1970
Pr
oper
ty s
tock
ed w
ith 4
0 ho
rses
that
mat
ed w
ith b
rum
bies
Er
nie
Mas
key
22
due
to la
ck o
f fen
ces
Bost
obri
ck S
tatio
n, 3
5 km
eas
t of G
FR
1880
s
Brum
bies
bre
d in
larg
e nu
mbe
rs w
ith fr
ee a
cces
s to
Er
ic F
ahey
19
or
igin
ally
par
t of G
uy F
awke
s St
atio
n th
ousa
nds
of a
cres
la
te 1
940s
H
orse
s fr
om T
he A
ustr
alia
n Li
ght H
orse
Bri
gade
turn
ed
Gly
nne
Tosh
41
ou
t int
o th
e G
uy F
awke
s ar
ea
Pant
ons
Cree
k to
Com
bolo
Sta
tion
1936
–37
Catt
le m
uste
r, n
o br
umbi
es s
ight
ed
Flet
cher
Bra
zier
24
in
the
Kitt
ys C
reek
MZ
area
G
FS a
nd L
GFS
18
90s
2 St
allio
ns, b
red
exte
nsiv
ely
for
over
seas
mar
ket
Er
ic F
ahey
18
e.
g. r
emou
nt tr
ade
for
Briti
sh A
rmy
in In
dia
Won
gwib
inda
Sta
tion
1920
s–30
s Th
ere
wer
e m
any
brum
bies
on
the
prop
erty
that
mus
t hav
e
Phill
ip W
righ
t 21
ex
iste
d fo
r a
num
ber
of y
ears
and
wer
e co
ntro
lled
by
shoo
ting
or tr
appi
ng fo
r st
ock
hors
es
Dya
mbe
rin
Stat
ion
1920
s 2
Stal
lions
for
bree
ding
, unk
now
n if
prog
eny
Pe
ter
Gow
er
22
beca
me
wild
in th
e Pa
rk a
rea
Braz
ier
fam
ily p
rope
rtie
s on
Pan
tons
Cre
ek
1920
–199
0s
Braz
iers
bre
d th
eir
stoc
k ho
rses
und
er ti
ght c
ontr
ol,
Flet
cher
Bra
zier
24
an
d fr
om ju
st a
bove
Lon
don
Brid
ge to
no
esc
apes
or
inte
r-br
eedi
ng. I
n 19
59 n
o br
umbi
es s
ight
ed
Pant
ons
Cree
k M
Z on
pro
pert
y, b
ut 1
7 ou
tsid
e th
e bo
unda
ry a
t Lon
don
Brid
ge
Won
gwib
inda
sid
e of
Abe
rfoy
le R
iver
at
19
59
Two
brum
bies
cau
ght,
bel
ieve
d to
hav
e be
en h
unte
d
Ian
Lupt
on
25
Kang
aroo
Cre
ek
out b
y Bo
ban
Tops
/Hut
sta
llion
s
Surv
eyor
s Sp
ur o
n A
berf
oyle
Riv
er
1975
Re
calle
d se
eing
bru
mbi
es fo
r fir
st ti
me
on th
e A
berf
oyle
Ri
ver
Dou
g Fe
rris
36
Chapter 2. Study Area 32
Brumbies have been sighted in various locations throughout the Park (Table 2.3), but
almost exclusively in the northern MZs since the 1930s (Heritage Working Party 2002a).
2.3.1 North-western management zones: Paddys Plateau, Bobs Creek, Pargo Creek
On the north-western side, Mornington Station is thought to be the source of
brumbies (to become feral horses) inherited with the gazettal of Paddys Plateau MZ and the
Gulf Country as Park (Figure 2.4). The station ran mobs of brumbies that were not shot or
culled until after the 1965 drought, when horse numbers were reportedly out of control
(Heritage Working Party 2002b) (Table 2.3). During the cull, horses were moved into the Gulf
Country and onto the GFR, in particular. Mornington was purchased by Ernie Maskey in 1970
and was stocked with at least 40 of his own stock-horses that inter-mingled with brumbies as
the country was un-fenced. Mornington included parts of Bobs and Pargo Creek (i.e. Gulf
Country) and Paddys Plateau MZs, in which the Boban Tops/Hut is situated (Figure 2.4).
Stock-horses and brumbies were known to be bred and consistently present in those MZs
and were the target of brumby running since the 1930s (Ernie Maskey pers. comm. in
MacDougall 2001) (Table 2.3). Around the 1930s, for example, locals were paid to shoot
brumbies on Boban Tops/Hut (Table 2.3) to control their numbers. The northern sections of
Bobs Creek MZ adjacent to the Sara River MZ both received a flow of horses and brumbies
from Broadmeadows Station along the Boyd River to the Sara River–GFR Junction (Heritage
Working Party 2002b). Given the proximity along the Sara River flats to the mouth of Pargo
Creek to Bobs Creek, brumbies probably continued into Pargo Creek MZ, which also received
an influx of horses from stations in the Mitchell Run on the Henry River to the west
(Figure 2.4). The Heritage Working Party concluded based on sightings and first-hand
accounts that horse numbers were consistent, but low, after the 1940s relative to an
apparent substantial increase in the early 1980s (Heritage Working Party 2002a). Thus,
brumby history was considered to be long with a greater number of horses in Figure 2.4.
Chapter 2. Study Area 33
Figure 2.4 Map of key locations mentioned in Table 2.3 and Section 2.2 and summarised into three levels of length of brumby occupation (minor, intermittent and long) combined with relative number of horses (low, medium and high). Notation as for Figure 2.3.
Chapter 2. Study Area 34
2.3.2 Northern-to-mid-north-eastern management zones: Lower Guy Fawkes River,
Kittys Creek, Mid Guy Fawkes River, Combolo, Marengo
The Brown family established three stations that encompassed what are now the five
aforementioned northern to mid-north-eastern Mzs of the Park, which have had an
uninterrupted grazing history since at least the 1870s (MacDougall 2001). From north to
south, Broadmeadows Station was occupied in 1861, Combolo Station in 1884 and Marengo
Station around 1850–1876 (Figure 2.4). It is thought that the Brown family bred the majority
of brumbies in those areas of the Park in the early 1900s (Heritage Working Party 2002b).
Oral history accounts suggest that brumby populations fluctuated more than in the areas
that are now the north-western MZs (Section 2.2.1), and thus were considered to have an
intermittent history in Figure 2.4. Brumbies were common up until the drought and
subsequent bushfires of 1915, when most succumbed to starvation (MacDougall 2001). The
MacDougall family purchased Marengo in 1895, and captured what were thought to be the
last of the Brown family’s brumbies in 1933 at Peak Creek in Kittys Creek MZ (Table 2.3). By
the mid-1940s to 1970s brumbies were beginning to re-appear in Kittys Creek, Marengo
Creek (including Housewater Creek) and Combolo MZs but sightings and first-hand accounts
were rare until after 1970 (Table 2.3) (Heritage Working Party 2002a).
2.3.3 Southern management zones: Aberfoyle, Kangaroo Creek and Pantons Creek
Brumbies were a common sight on Wongwibinda Station adjacent to Kangaroo
Creek MZ in the 1920–30s when they were controlled by shooting and trapping (Table 2.3).
Similarly, Dyamberin Station had a history of breeding stock horses in the 1920s and it is
unknown if horses escaped to become brumbies (MacDougall 2001). Since the 1950s, just
two sightings of a total of three brumbies in Kangaroo Creek and the Aberfoyle River MZs
were believed to have come from Boban Tops/Hut (Heritage Working Party 2002b). It
appears that the early settlement stock-horses and brumbies did not persist in these areas
and domestic horses on neighbouring pastoral properties have been contained since
(Heritage Working Party 2002a). Thus brumby history was considered to be nil to minimal in
these areas in Figure 2.4.
Chapter 2. Study Area 35
2.4 Feral horse history of monitoring and control in GFRNP
2.4.1 Monitoring prior to the October 2000 cull (1981–2000)
NPWS conducted helicopter-surveys of cattle and horses in a standardised manner,
with flight paths following a zig-zag pattern along the rivers, creeks and adjoining slopes, as
flat ground is generally only associated with the riparian flats (Heritage Working Party
2002a). Feral horses are more visible in such areas and tend to head to open, flat areas when
mustered. The early helicopter-surveys (1981–82) were opportunistic counts of horses
whilst monitoring cattle incursions. Thus, surveys were biased towards the mid-eastern MZs
containing a greater proportion of the GFR flats, and other tracts of flat ground such as the
Fattening Paddock (Figure 2.5). Pantons Creek, Pargo Creek and the southern half of Bobs
Creek were not yet gazetted, and as the Sara River and northern Bobs Creek MZs were not
commonly utilised by cattle, they too were not surveyed (Table 2.4). In 1981–82, a greater
number of horses were counted in the Lower GFR, followed by Mid GFR and Kittys Creek MZs
with nil to minimal horses in the south-eastern MZs (Table 2.4). After December 1996,
Pantons Creek MZ was included in all but one survey as it was small in size, oriented north–
south, continuous with GFR and required little additional effort (Figure 2.5). According to
local stockmen and NPWS field staff, horses were not present in Kangaroo Creek MZ, and
incursions were minor in the Aberfoyle River MZ, tending to be limited to the GFR Junction.
Helicopter-surveys in December 1998 recorded no horses in both MZs (Table 2.4), with the
result repeated for Kangaroo Creek MZ in May 2004 (Table 2.5). A total of six horses were
counted in the Aberfoyle River MZ in the October 2000 cull (Table 2.5), again at the GFR
Junction, perhaps fleeing into the area in response to the helicopter (Figure 2.6).
In the December 1996–98 helicopter-surveys, more horses were counted in the Mid
GFR and Kittys Creek MZs. In the 1996 and 1997 helicopter-surveys, Bobs Creek itself was
included (Figure 2.6). In 1998, only the small area of Bobs Creek MZ that adjoins the Sara
River MZ was surveyed and not the creek itself, which may explain the lower counts
(six horses) relative to previous years (11–15 horses) (Table 2.4). During this period, as
explained in Table 2.1, Bobs Creek MZ was much smaller (1100 ha) than the other MZs with
horse populations. In 1998, only a relatively small stretch of the Sara River MZ (from GFR
Junction to the mouth of Bobs Creek) was surveyed for the first time, with the number of
horses counted comparable to Combolo and Lower GFR MZs (Table 2.4).
In May 2000, in addition to the eight MZs in which horses had previously been
counted, Pargo Creek was gazetted and included in the total count of 180 horses (Table 2.4).
Chapter 2. Study Area 36
Five months later, an additional 103 horses were counted in the same areas with one less
MZ, Kittys Creek, where previous counts had been high (Figure 2.6). Kittys Creek MZ was not
included as counts were made on 18 October 2000 during wild fire control operations and
the survey was restricted to the valleys adjacent to the GFR and Sara River (Heritage Working
Party 2002a). The GFR flows around Kittys Creek MZ through the Mid GFR MZ (Figure 2.5).
The wild fire burnt almost 60% of the Park area from early September (English 2000) and may
have been less intense on the green river flats adjacent to permanent water, leading to the
concentration of horses in those areas.
Table 2.4 Summary of the number of horses counted in each management zone (MZ) and total number of horses across the Park from helicopter-surveys conducted by NPWS Dorrigo Plateau Area office, from 1981 to prior to the cull in 2000. The 2000 helicopter-survey shapefiles had Global Positioning System (GPS) coordinates but no accompanying number of feral horses in the mob and thus were combined (Comb.) for the MZs surveyed. NG: not yet gazetted as Park, NS: not surveyed, '–' indicates a missing data entry, (no information available).
MZ code MZ name
Dec. 1981
June 1982
Dec. 1996
Dec. 1997
Dec. 1998
May 2000
Pre-cull survey
Oct.2000
1 Pantons Creek NG NG 0 0 0 0 NS 2 Upper GFR 2 0 7 6 1 Comb. Comb. 3 Marengo 0 0 2 0 5 Comb. Comb. 4 Aberfoyle River NS NS NS NS 0 NS NS 5 Combolo 2 1 17 0 17 Comb. Comb. 6 Mid GFR 27 – 90 47 53 Comb. Comb. 7 Kittys Creek 18 12 52 52 30 Comb. NS 8 Paddys Plateau NS NS NS NS NS NS NS 9 Bobs Creek NS NS 11 15 6 Comb. Comb.
10 Pargo Creek NG NG NG NG NG Comb. Comb. 11 Sara River NS NS NS NS 21 Comb. Comb. 12 Lower GFR 39 34 NS NS 19 Comb. Comb.
13 Glen Nevis Plateau NS NS NS NS NS NS NS
14 Kangaroo Creek NS NS NS NS 0 NS NS Total number of horses 88 47 179 120 152 180 283
Chapter 2. Study Area 37
Figure 2.5 GPS location of horse mob sightings from helicopter-survey counts in Table 2.4, showing the distribution of horses in MZs in relation to rivers and creeks. Notation as for Figure 2.3.
Chapter 2. Study Area 38
2.4.2 Management pre and post-cull, and monitoring post-cull (2000–2007)
From 1972 to the early 1990s, horses in the Park were not managed (NSW NPWS
2006b). As substantial areas were added to the original 1972 Park extent, graziers left with
most of their cattle and horses but due to the expansive rugged terrain and minimal fencing,
some horses remained (Ballard 2005). It is also the general opinion of local graziers that
brumbies were bred to be strong, and with no natural predators and local management, in
those ensuing years the populations increased to numbers larger than those recalled for the
period 1900–1965 (MacDougall 2001).
Active management of the horse population began in 1992. Various methods were
trialled, but up until 2000, horses were trapped and mustered predominantly by men on
horseback, occasionally assisted by helicopter (NSW NPWS 2006b). Over that period,
156 horses were removed from the Park, mostly from Broadmeadows along the Boyd River
and GFR in the Lower GFR, Kittys Creek, Combolo and north-eastern corner of
Bobs Creek MZs (D. O’Brien and G. Baldwin pers. comm.).
The largest control operation in the Park occurred on 22–24 October 2000 when a
total of 606 horses were culled from helicopters (English 2000). Of the 606 horses shot,
373 horses were assigned a specific GPS coordinate. Given that 41 ‘unknowns’ were in the
Mid GFR MZ compared to ≤four unknowns in any other MZ, it can be assumed that almost all
of the remaining 233 horses were in the Mid GFR. This assumption was also consistent with
the 1981–2000 helicopter-surveys where horse counts tended to be greatest in the
Mid GFR MZ from 1996–1998 (Table 2.4). Kittys Creek and Bobs Creek MZs recorded a
similar and the next largest number of kills. The density of kills would have been much
greater in Bobs Creek MZ as in Figure 2.6 only the northern section was included in the cull
(1100 ha) while the entire Kittys Creek was surveyed (3700 ha). Similarly, in the
Sara River MZ, the cull focused on the eastern half along the Sara River, with approximately
half the number of kills as Bobs and Kittys Creek MZs.
Chapter 2. Study Area 39
Figure 2.6 GPS location of horse mob sightings corresponding to helicopter-survey counts showing the distribution of horses in management zones in relation to rivers and creeks for the 22–24 October 2000 cull (Table 2.5) and for the comprehensive 2006 helicopter-survey. Notation as for Figure 2.3.
Chapter 2. Study Area 40
Table 2.5 Summary of the number of horses shot (October 2000 only) or counted (2001–2005) in each management zone (MZ) and total number of horses across the Park. Survey method as in Table 2.4. UK: unknown number of horses in the mob shot at that location, only GPS coordinate provided, NS: not surveyed.
MZ code MZ name 22–24 Oct. 2000 cull
April 2001
May 2004
7 April 2005
12 April 2005
1 Pantons Creek 0 NS 0 NS NS 2 Upper GFR 5 (1UK) NS 9 NS NS 3 Marengo 12 NS 0 NS NS 4 Aberfoyle River 6 NS NS NS NS 5 Combolo 8 5 0 NS NS 6 Mid GFR 64 (41UK) 3 14 NS NS 7 Kittys Creek 79 (2UK) NS 3 NS NS 8 Paddys Plateau NS NS 29 NS NS 9 Bobs Creek 89 27 23 62 46
10 Pargo Creek 11 16 20 54 33 11 Sara River 44 16 15 NS NS 12 Lower GFR 7 (4UK) NS 9 NS NS
13 Glen Nevis Plateau NS NS 0 NS NS
14 Kangaroo Creek NS NS 0 NS NS
Total number of horses 373 (606 including
UKs) 67 122 116 79
Paddys Plateau was exempt from the cull as it is one of the few MZs with vehicle and
public access, and is surrounded by a number of grazing properties. Hence, the estimated
80 horses that remained after the cull (English 2001b) were concentrated mostly on Paddys
Plateau. It is thought, based on NPWS field staff observations, the presence of extensive
horse track networks and ground survey counts by Schott (2003), that numbers of horses
move seasonally between the eastern half of the Sara River, Bobs and Pargo Creek, and
Paddys Plateau MZs (NSW NPWS 2006c). The April 2001 helicopter-survey after the cull
therefore focused on those three MZs and the Mid GFR where kills during the cull were
concentrated (and Combolo MZ due to proximity and inclusion of the GFR). Counts were
greatest in Bobs Creek MZ (27 horses), and equal in Pargo Creek and the Sara River MZs
(16 horses), and comparatively low in Mid GFR MZ with just three horses counted and
five horses in Combolo MZ. This result was consistent with the seasonal migration
mentioned previously for the western block of MZs and suggests that, in the period
immediately after the cull, horses re-colonised Bobs Creek, Pargo Creek and the Sara River
MZs. The trend continued in the May 2004 helicopter-survey, which included the additional
four MZs with historical counts of horses. Counts were greater in the western block of MZs,
with no horses counted in Combolo and Marengo and just three horses in Kittys Creek.
Chapter 2. Study Area 41
Paddys Plateau was included for the first time and an additional six–nine horses were
counted than in Bobs and Pargo Creek MZs. However, Paddys Plateau is 2–3.7 times greater
in area than Bobs Creek and Park Creek, thus the density of horses was greater in the latter
MZs. In support of this assessment, Bobs and Pargo Creek were selected by the NPWS
Dorrigo Plateau Area office and Vernes et al. (2009) for a novel mark–recapture technique to
estimate peak feral horse densities in the Park. As the southern half of Bobs Creek had been
gazetted in 2000 the entire MZ was surveyed in the 2005–2007 helicopter-surveys. From the
7 and 12 April 2005 helicopter-surveys, a total of 164 individual horses were photographed
and identified and the combined density of horses in Bobs and Pargo Creek MZs estimated at
0.038 horses/ha (upper and lower 95% confidence limits [CL] = 0.035–0.057 horses/ha). The
technique was repeated in May 2006 and 2007. In 2006 a total of 115 individual horses were
identified but recaptures were insufficient to estimate density. The 2006 survey also
included the Sara–GFR Junction, Kittys Creek and the MZs associated with the GFR. The
largest number of mobs and horses were again counted in Bobs and Pargo Creek MZs
(Figure 2.6). In 2007, the portion of the Sara River MZ along the Sara River that adjoins Bobs
and Pargo Creek MZs was included with a total of 236 individuals identified and density
estimated at 0.023 horses/ha (CL, 0.021–0.034 horses/ha). The change in density from 2005
to 2007 followed horse control (passive trapping and removal) on the Sara River at Ballards
Flat and upstream of the Sara River–Bobs Creek Junction.
2.5 Recent history of cattle incursions in GFRNP
Feral cattle and horses have been concurrent management issues, with 151 cattle
sighted in addition to the 283 horses along the Sara–GFR Junction flats and the flats of the
GFR in the 18 October 2000 helicopter-survey. The MZ, number of cattle in each mob and
total number of cattle sighted in MZs in the Park in 1995, 1997, 1998 and 1999 are
summarised in Table 2.6 and the specific GPS locations provided in Figure 2.7. Both
represent the typical distribution patterns of cattle in the Park prior to the start of this
project. Cattle mobs have been mostly associated with riparian flats adjacent to the Boyd
River and mid to lower GFR, and with the higher plateau country in the vicinity of the
Fattening Paddock (Figure 2.7). More often than not, multiple mobs of cattle were counted
in Combolo and Upper GFR MZs in all four survey-years, with a peak MZ total of 171 cattle in
Combolo in 1998. The Fattening Paddock (within GFR State Conservation Area) did not
record cattle every survey-year, but totals were relatively high (70 and 204 cattle). Cattle
Chapter 2. Study Area 42
incursions were also reasonably frequent with some large mobs (e.g. 80 cattle in 1998,
Table 2.6) in Marengo MZ, and to a lesser extent in the Mid and Lower GFR MZs.
Table 2.6 Summary of NPWS Dorrigo Plateau Area office helicopter-survey counts of cattle mob incursions in the Park in 1995–1999, corresponding to Figure 2.7. Individual numbers separated by a comma represent the number of cattle in one mob per GPS location with the total number of cattle per management zone (MZ) each year in bold and parentheses.
Several local stockman who ran cattle in the Park or in similar country (e.g. Brian
Fahey, Doug Ferris) and NPWS field officers and rangers (Tony Prior) were of the opinion that
cattle activity was concentrated on the riparian flats and adjoining lower slopes along the
major river systems, and cattle had to be forcibly mustered up moderate (6–18°) or steep
slopes (18–30°) (McDonald et al. 1990). The GPS locations of cattle mobs in Figure 2.7 were
overlayed on a raster slope grid that was classified into four slope classes. As predicted,
almost all cattle sightings were associated with flat or gently sloping ground (<10°).
Cattle counts in the Aberfoyle River were limited to the GFR Junction area (Figure 2.7)
and coincided with several letters of complaint from bush-walkers at the Aberfoyle–GFR
Junction in the mid-1990s. No cattle were sighted in Pargo Creek MZ, and just the one mob
of 6 cattle in Bobs Creek MZ along the creek (Table 2.6). Cattle in the Sara River MZ tended
to favour the larger Ballards Flat area (Figure 2.7) or flats along the Sara River and rarely
strayed up into the precipitious Bobs and Pargo Creeks, the entrance being obscured by a
rocky cliff in Pargo Creek MZ. Similarly, the Brazier family own land adjacent to the Park and
in 2009 sold the Pargo Flat parcel on the elevated plateau above Pargo Creek MZ to the
NPWS (Figure 2.7). Pargo Flat was optimal for grazing cattle but mostly adjoins Pargo Creek
MZ along a sharp, rocky cliff that prevents cattle from accessing the MZ (Terry Brazier pers.
comm.).
MZ Code Management Zone 1995 1997 1998 19992 Upper GFR 7, 7, 11, 33 (58) 3, 6, 8, 23 (40) 50 11, 41 (52)3 Marengo 0 4, 5, 9, 9, 9 (36) 80 524 Aberfoyle River 0 5, 5 (10) 97 05 Combolo 1, 6, 12, 14 (33) 8, 12, 60 (80) 34, 40, 97 (171) 236 Mid GFR 5 12, 12, 15, 16, 16 (71) 0 07 Kittys Creek 4 0 0 169 Bobs Creek 0 0 0 6
10 Pargo Creek 0 0 0 011 Sara River 6, 10, 18 (34) 0 0 1212 Lower GFR 52 0 0 20
Fattening Paddock 0 10, 18, 21, 21 (70) 5, 5, 14, 15, 15, 20, 50, 80 (204) 0
Chapter 2. Study Area 43
Pantons and Kangaroo Creek MZs were not included in helicopter-surveys even
though both MZs had a history of and still incur periodic cattle incursions from neighbouring
pastoral holdings. Instances of cattle incursions have become minimal in the last 10–
20-years with generational change (Tony Prior pers. comm.). Only a few remaining stockman
are willing and able to camp and muster cattle remotely for any length of time. According to
neighbouring pastoral property owners, encroachment is also limited temporally and
spatially, occurring over winter with mobs of cattle of between 20 and 50 beasts and on the
same few select routes (Doug Ferris and Andy Winkle pers. comm.).
The western section of Paddys Plateau MZ adjoins grazing properties but is well
fenced and has one of the Park’s few developed vehicle tracks. Cattle incursions have
occurred on occasion south-west of Wonga Hut, but given the proximity to the Tallagandra
depot and good access, NPWS field staff have quickly yarded and removed cattle once
sighted. NPWS staff confirmed that there were no records or known instances of graziers
droving cattle into Pargo or Bobs Creek since 1972, consistent with oral histories that
confirmed cattle were not run in Bobs and Park Creeks MZs prior to 1972.
Chapter 2. Study Area 44
Figure 2.7 GPS locations of cattle mob sightings in the Park in 1995 and 1997–1999 overlayed on a slope classification. Notation as for Figure 2.3.
Chapter 2. Study Area 45
2.6 Selection of management zones for the landscape-scale survey (Chapter 6)
The catchment survey was conducted at a landscape scale corresponding to the size
of the MZs or catchments. It required two catchments occupied by horses to represent the
‘horse’ (H) level of the Treatment factor, and two catchments to represent the ‘non-horse’
(N-H) level. If possible, all catchments would also have nil to minimal cattle use, both past
and present. Of the 14 MZs, nine have been populated by horses to some extent with the
total area of declared Wilderness in the Park under feral horse occupation estimated at
34 000 ha (40%) in 2006 (NSW NPWS 2006c). From Sections 2.1–2.5, the prime candidates
for the horse catchments were Bobs and Pargo Creek. Both have one of the longest and
most consistent history of horses, and the greatest density of horses after the 2000 cull to
the present day. Just as importantly, the relative scarcity of riparian flats and their smaller
size made them unsuitable for cattle and on the whole, these catchments were not used by
graziers for running mobs of cattle during any period since European settlement. The Mid
GFR MZ would have been suitable in terms of horses, but was confounded by the presence of
cattle, as were parts of the Sara River, Combolo, Upper and Lower GFR and Marengo MZs.
Cattle incursions into Kittys Creek MZ appeared minimal, but the early horse history was
intermittent and horses did not re-colonise the area to the same extent as Bobs and Pargo
Creeks after the cull.
From Sections 2.1–2.5, candidates for the non-horse catchments were Kangaroo and
Pantons Creek. Kangaroo Creek and Pantons Creek MZs, in particular, had no history of feral
horses, and minimal history of brumby and stock-horse use. The Aberfoyle River MZ was
considered, but potentially had some brumby and feral horse use in the late 1960s to late
1980s. In all three MZs, cattle incursions occurred occasionally but were not of intensity
(cattle numbers) or frequency to attract sufficient attention.
Chapter 3. Indirect Effects on Macropods 46
CHAPTER 3.
INDIRECT EFFECT OF FERAL HORSES ON THE SPATIAL DISTRIBUTION OF MACROPODS
3.1 INTRODUCTION
In Australia, feral horses may compete with wildlife, notably macropods, for food,
water and space (Olsen and Low 2006; Nimmo and Miller 2007), but the evidence is
equivocal. In the Northern Territory (NT), Berman and Jarman (1988) reported a negative
correlation between the presence of macropod dung and horse dung at some sites and
concluded that by removing the herb layer, both horses and cattle appeared to influence
wildlife. However, replication was limited to one site with horses and no cattle and cattle
and macropod dung were negatively correlated at all other sites (Berman 1991). Similarly,
after 6000 feral horses were removed from Finke Gorge National Park in central Australia,
the amount of fresh black-footed rock wallaby (Petrogale lateralis) dung was observed to
steadily increase from zero over a period of 10 years (Matthews et al. 2001). While the
correlation was ‘striking’, cause (horse removal) and effect (increase in rock wallabies) could
only be inferred (Matthews et al. 2001). The study was uncontrolled and unreplicated and
no data were presented or available upon request (Edwards et al. 2003; Glenn Edwards, pers.
comm.). In the west MacDonnell Ranges, NT, the historically rare central rock-rat (Zyzomys
pedunculatus) was presumed extinct in 1990 after not being recorded for 36 years, but was
rediscovered in 1996, with 40 individuals live-trapped at 11 sites since then (Nano et al.
2003). The authors speculated that the recent increases in abundance of the central rock-rat
were due to the removal of more than 30 000 feral horses from the west MacDonnell Ranges
over the past 15 years (Bryan 2001). In GFRNP, after 606 horses were culled in
October 2000, eastern grey kangaroos (Macropus giganteus) were observed by NPWS staff
to rapidly colonise the grassy river flats in ‘unprecedented numbers’ (Tony Prior, pers. comm.
in Olsen and Low 2006). The first three studies mentioned previously are assumed to reflect
resource or exploitative competition given they were in semi-arid environments where
resources tend to be limited and localised (Noy-Meir 1973; Caughley 1987). In the case of
the central rock-rat, the major food plants identified in their diet were also palatable to
stock, including horses (Nano et al. 2003).
In riparian flush zones and around watering points in semi-arid environments, feral
horses remove almost all available herbaceous biomass (Beever and Brussard 2000a; Seliskar
2003). In the USA, key resource locations are where resource and indirect interference
Chapter 3. Indirect Effects on Macropods 47
competition between both feral horses and feral burros (Equus asinus) and native ungulates
such as desert bighorn sheep (Ovis canadensis) are most likely to occur (Dunn and Douglas
1982; Berger 1985, 1986; Marshal et al. 2008; Ostermann-Kelm et al. 2008). Manipulative
field experiments to test the mechanism underlying competitive relationships are rare
because they are notoriously difficult and can be expensive to implement under natural
conditions (Stewart et al. 2002). The potential for exploitative competition is thus inferred or
modelled on the degree of overlap in feeding strategies and diet, as significant overlap in
resource utilisation invariably leads to competition and the competitive exclusion of some
species (Pulliam 1986).
Regardless of the mechanism involved, an overlap in species’ habitat preferences is a
necessary precursor to interspecies interactions (Araujo and Luoto 2007) and patterns of
habitat use in grassy woodland appear to be very similar for feral horses and eastern grey
kangaroos. Both select alluvial grasslands with a mixture of forbs and short grasses or mesic
flush zones in hillside depressions (gully lines), followed by open grassy woodland, and both
avoid habitats with dense, shrubby undergrowth (Taylor 1980; Landsberg and Stol 1996;
Walters 1996; Linklater et al. 2000; Veltman 2001; Lamoot et al. 2005). Dung is an indirect
method used to infer the presence of an animal in an area (Wilson and Delahay 2001; Sadlier
et al. 2004). Dung counts have been used to determine the grazing distribution of horses and
eastern grey kangaroos as both species defecate where they graze (Hill 1981; Johnson and
Jarman 1987; Walters 1996; Lamoot et al. 2004). In the present study, the NSW NPWS
commissioned a horse capture and removal program that provided an opportunity to assess
changes in macropod dung in relation to the manipulated abundance of horses. Dung
transects were monitored at the district scale (100 ha) in Paddys Plateau catchment, at the
site (0.01 ha) and district scale (4 × 1 km) in Bobs Creek catchment, and at the catchment
scale (5000 ha) to determine if the removal of horses coincided with increased macropod
activity. If so, it would provide support for the hypothesis that horses affect the feeding
distribution of macropods.
Chapter 3. Indirect Effects on Macropods 48
3.2 METHODS
3.2.1 Paddys Plateau dung transects and horse removal program
3.2.1.1 Dung transect zones
For the Paddys Plateau exclosure experiment, six sites were selected >1 km from
each other. Information in Chapter 2 on horse distributions and seasonal movement
patterns, NPWS field staff experience and knowledge, and personal observation suggested
that sites were located along a grazing gradient. Sites 1, 2 and 3 were located in the mid-
section of the Plateau between the Aberfoyle River catchment, which did not have a resident
horse population, and the south-western tip of Bobs Creek catchment (Figure 3.1). No
horses have been sighted or shot in the south-western tip of Bobs Creek (Chapter 2,
Figure 2.5 and 2.6). Sites 4, 5 and 6 in the eastern section of Paddys Plateau were separated
from Sites 1–3 by a narrow spur. The eastern section was adjacent to three horse-occupied
catchments: the mid to northern section of Bobs Creek, the southern half of Kittys Creek, and
the south-western tip of Combolo (Figure 3.1). Kittys Creek tributary runs back into the
Boban Hut area, and was thought to be a historical migration conduit for brumbies (and later
feral horses) prior to the 2000 cull (MacDougall 2001). In the recent May 2006 heli-survey,
horses were not sighted within 4 km of the Paddys Plateau and Kittys Creek catchment
boundaries (Figure 2.6). However, horses were sighted near the Travelling Stock Route (TSR)
adjacent to Site 4 that connects Combolo catchment to the Boban Hut area (Figure 3.1). The
TSR continues on from Boban Hut along the escarpment edge of Bobs Creek. The dung
transects for Sites 5 and 6 were next to the Bobs Creek escarpment, which overlooks Bobs
Creek and is connected to the other catchments with high densities of horses after the cull,
Pargo Creek and the Sara River flats (e.g. Ballards Flat) (Figure 3.1). Visual inspection of the
two catchments confirmed the presence of an extensive, well-developed or worn horse track
network (based on degree of soil surface hardness, depth and width of track and signs of
sheeting or gully erosion) connecting them. Several reports had also documented a high
concentration of signs of horse activity, such as bark-chewing on trees and well-worn salt
licks (salt deposits that herbivores regularly lick to obtain mineral nutrients such as calcium,
sodium and iron; Kreulen 2008) in the area (Schott 2002, 2003; Ashton 2005). Horses may
use the Paddys Plateau–Bobs Creek migration conduit either to obtain nutrients or to find
mates in the case of dispersing off-spring, in addition to the seasonal migration discussed in
Chapter 2. Site 5 (Boban Hut) appeared to be the central point of dispersion for migrating
horses, followed by Site 6 (Spion Kiope). Both sites were named after their proximity to
Chapter 3. Indirect Effects on Macropods 49
trapping yards by the same name (Section 3.2.1.3). In addition, once trapping started, horses
were not removed at the Boban Hut trap site until 5 months later (September 2004) than the
trap sites associated with Sites 1–3 (April 2004), and at Spion Kiope later still (October 2005).
Thus, horse grazing pressure was potentially greater historically in and around Sites 4–6 and
greater during the experiment, with horses persisting longer in Sites 4–6 than Sites 1–3 after
the commencement of the trapping program in April 2004.
3.2.1.2 Dung transect design and monitoring
Twelve permanent dung transects were established in a dung transect zone
surrounding each of the six exclosure sites on 1–9 July 2005. Transects were monitored an
additional three times: 7–12 November 2005, 12–18 March 2006 and 13–19 July 2006. On a
topographic map (Kookabookra 9337-IV-N, 1:25,000), the 100-ha Universal Transverse
Mercator (UTM) grid containing the exclosures for Sites 1–3 were selected as the dung
transect zone for the corresponding site (Figure 3.1). For Sites 4–6, grids containing
exclosures bordered each other. Spatial separation or independence between dung
transects zones was obtained by selecting an adjacent grid (Figure 3.1). The starting points of
dung transects within the 100-ha grid were chosen randomly using the Random Generator in
Excel 2003. The compass orientation of the transect line was determined the same way.
Dung transects were 50-m long and dung deposits recorded 5 m either side of the transect in
a quadrat of 0.05 ha.
Chapter 3. Indirect Effects on Macropods 50
Figure 3.1 Location of exclosure sites and dung transect zones relative to trap sites and the Bobs Creek Sara River migration conduit. The termination point of Bobs Creek tributary and the topography of Paddys Land relative to neighbouring catchments are shown using multispectral SPOT 5 imagery. The SPOT 5 image was captured on 26 May 2005; pixel resolution is 10 m (DNR 2005).
Dung of the large grazing herbivores of interest, horses and macropods, was counted
and then raked clear of the transect line. A dung pile (referred to as a deposit) consisted of
numerous individual pellets of horse or macropod dung. Horse dung was counted as one
deposit as long as pellets were grouped together in one pile or if there was a pile of decayed
dung, even without discernable pellets. Individual scattered pellets associated with an
adjacent dung deposit were not counted. Macropod dung was counted if pellets were
grouped into one pile or if there were one or two individual pellets not clearly associated
with, or located next to, another dung deposit. Otherwise pellets were judged to be
separate deposits on the basis of distance, pellet size, shape and age according to Hill (1978).
The different detection probabilities associated with horse and macropod dung were
recognised and controlled for at the outset of the experiment. Horse dung deposits were
large and immediately visible to the naked eye from a distance. Macropod dung was smaller
and could be covered or camouflaged by litter or tussock foliage. Thus, an intensive search
protocol was used for macropod dung (e.g. a stick was used to scratch through shallow litter
Chapter 3. Indirect Effects on Macropods 51
piles and dense piles of leaf litter, bark or tussock vegetation was searched by hand). Any
objects similar to macropod pellets, such as rocks and dirt or seed pods, were examined and
sometimes checked by crushing them.
The most abundant macropod species on the plateau and in the Park was the eastern
grey kangaroo, followed by the red-necked wallaby (Macropus rufogriseus) (NSW NPWS
2009a and K. Vernes pers.comm.). Eastern grey kangaroo deposits were distinguished from
red-necked wallaby pellets after Johnson and Jarman (1987). The approximate time interval
between dung counts was 4 months. Given differences in the size and volume of macropod
and horse dung, it was possible that some macropod dung may have decayed and
disappeared within this interval and was underestimated (Appendix 2).
When transects were established, detailed descriptions were made and
photographs taken of the habitat surrounding each transect, including the dominant
composition and relative density and height of the groundstorey, understorey and canopy
layer. Transects were allocated post-data collection to one of four habitat types: (1) grassy
woodland (GW), (2) shrubby woodland (SW), (3) grassy swale (GS) and (4) track (T).
Grassy woodland (GW) had a groundstorey projective foliage cover of 10–30% and
trees 10–30 m tall, with a well-developed herbaceous stratum in which grasses were
prominent (70–100% cover) and shrubs poorly developed or absent (Figure 3.2). In the
southern half of Australia, this community has been subjected to stock grazing (Specht 1970).
The open structure was easily traversed, and palatable tussock grasses such as kangaroo
grass (Themeda australis), tussocky poa (Poa sieberiana), wild sorghum (Sarga leiocladum),
and barbed wire grass (Cymbopogon refractus) were abundant and accompanied by patches
of the highly palatable, year-long green, perennial grass, weeping grass (Microlaena
stipoides), and legumes such as slender tick-trefoil (Desmodium varians). The other
dominant structural formation on Paddys Plateau was grassy, open forest with a foliage
cover of 30–70% (Specht 1970). The herbaceous stratum was as well-developed and grasses
as prominent (70–100% cover) as grassy woodland but shrub development may have been
slightly greater at times due to the potential for greater shrub recruitment. A few transects
were located in the transition zone between grassy woodland and grassy, open forest.
Chapter 3. Indirect Effects on Macropods 52
Figure 3.2 Grassy woodland dung transect.
Shrubby woodland (SW) transects had the same groundstorey structure and often
extended into grassy woodland, but were distinguished by having ≥50% of the transect in
dense pockets of shrubs usually with a sparser herbaceous layer (Figure 3.3). The abundant
shrubs were dominated by understorey species such as acacias (Acacia spp.), melaleucas or
paperbarks (Melaleuca spp.) and sheoaks (Allocasuarina spp.). At times, the shrubby layer
and seedlings formed dense thickets that were either difficult to traverse or impenetrable.
Some sections of the groundstorey were comprised of rocky infertile soils and patches of
bare ground, some were covered by gap-colonising, carpet-forming forbs such as kidney
weed (Dichondra repens), while others were dominated by fine and coarse litter and woody
debris or less palatable grasses such as blady grass (Imperata cylindrica). Shrubby woodland
transects sometimes had patches of a palatable, grassy, ground layer (Figure 3.4). However,
such vegetation in general was cluttered and the herbaceous biomass was patchy.
Chapter 3. Indirect Effects on Macropods 53
Figure 3.3 Cluttered section of shrubby woodland with a horse in the background.
Figure 3.4 Comparatively open section (foreground) in shrubby woodland.
Grassy swales (GS) occurred in grassy woodland and consisted of open treeless and
shrubless drainage lines and swales; they appeared to have better moisture and fertility
status than adjacent grassy woodland (Figure 3.5a). Weeping grass was more common in
this habitat type than others, and some transects were grazing lawns (Figure 3.5a and b).
Grassy swales were frequently observed being grazed by mobs of macropods or horses.
Chapter 3. Indirect Effects on Macropods 54
Figure 3.5 (a) A grassy swale with a ground layer dominated by weeping grass, adjacent to grassy woodland.
Figure 3.5 (b) A grassy swale consisting of a grazing lawn.
Chapter 3. Indirect Effects on Macropods 55
The final habitat type, ‘track’ (T), referred to transects in one of the three
aforementioned habitat types but which also dissected or ran parallel to a vehicle track
(Figure 3.6). At Site 5, tracks were major horse tracks, which were prevalent; vehicle tracks
were not present in that dung transect zone. Tracks probably incurred more use by horses
than shrubby woodland as they provided an efficient means of moving between areas of the
plateau, for example, to known dam locations or mineral sources.
Figure 3.6 Vehicle track transect in grassy woodland.
As transects were not stratified by but assigned to habitat type post-hoc for the
purpose of analysis, the number of transects in each habitat type differed between zones
(Table 3.1). Grassy (34.7%) and shrubby (33.3%) woodland had the most transects, followed
by grassy swale (19.4%) and track (12.5%). In Sites 1–4, there were generally four to five
transects in grassy woodland, three to four transects in shrubby woodland, and one to
Chapter 3. Indirect Effects on Macropods 56
three transects in grassy swale (Table 3.1). However, in Site 5, six transects were shrubby
woodland and Site 6 had four grassy swale and three grassy woodland transects.
Table 3.1 Number and proportion (in parentheses) of dung transects in each site (12 transects) in the four habitat types. The total number of dung transects in each habitat type was unequal, and are italicised in the bottom row.
Grassy Shrubby Grassy woodland woodland swale Track Site 1 4 (0.33) 4 (0.33) 3 (0.25) 1 (0.08) Site 2 4 (0.33) 4 (0.33) 2 (0.17) 2 (0.17) Site 3 5 (0.42) 4 (0.33) 1 (0.08) 2 (0.17) Site 4 5 (0.42) 3 (0.25) 3 (0.25) 1 (0.08) Site 5 4 (0.33) 6 (0.50) 1 (0.08) 1 (0.08) Site 6 3 (0.25) 3 (0.25) 4 (0.33) 2 (0.17) Total 25 24 14 9
Horse deposits were photographed and described. Descriptions included the number
of intact or recognisable individual pellets, relative size (e.g. small to large pellets >10 cm in
length), presence of vegetation or fungi growing out of the dung deposit, colour and
moisture content, and an assessment of the extent of weathering and decay. Dung counted
at the first sampling time in July 2005, when the dung transects were established, had
accumulated over an undefined period. Subsequent sampling times in November 2005,
March 2006 and July 2006 meant that dung accumulated over approximately 4 months
between each sampling time as the transects were cleared of dung at each reading. In New
Zealand’s Kaimanawa Mountain Range, the average decay time for dung to be no longer
visible from a distance of 1.5 m was 424 ± 34 days with most dung disappearing in just over
1 year (Linklater et al. 2001). Published information on the relationship between the
numbers of intact individual pellets in a dung deposit of different ages was unavailable, but
old dung deposits tended to have the greatest number of plant and fungi species growing
directly in the dung deposit (Loydi and Zalba 2009). In order to compare the July 2005
accumulation period to the subsequent accumulation periods, the average number of intact
individual pellets from dung deposits at June 2006, which was 12 pellets, was used as a
reference point. Any dung deposits with ≤11 intact individual pellets or the presence of fungi
and vegetation were excluded. Of the total dung deposits counted in July 2005, 64.5% were
eliminated and the accumulation period estimated to be an equivalent 4 months.
Chapter 3. Indirect Effects on Macropods 57
3.2.1.3 NSW NPWS capture and removal program
The Dorrigo Plateau Area office of the NSW NPWS initiated a program in April 2004 to
trap and remove horses from Paddys Plateau. The program was repeated in 2005 and 2006.
The trapping program is described in detail and accompanied by a comprehensive summary
of trap records, including demographic data, in Appendix 3. Trap records included the
capture date and location of each horse. Seven trap sites were used (Figure 3.1). Trap sites
at Wonga Flat, Mt Gardiner Plateau and Perrys Yards were closest to Sites 1, 2 and 3 at a
distance of 5–7 km (approximate straight line distance). Ryans Paddock trap site was
between Sites 1 and 2 at a distance of 0.5 km, and Middle Dam trap site was near Site 3.
Spion Kiope trap site was <2 km from Site 6 and Boban Hut trap site was <1 km from Site 5.
Due to the potential difference in horse grazing pressure between Sites 1–3 and
Sites 4–6 and location of trap sites relative to exclosure sites, trap records were summarised
in relation to the two respective groups of trap sites, dung accumulation periods and trap
periods (Table 3.2). Horse captures at Wonga Flat, Perrys Yards, Ryans Paddock, Mt Gardiner
Plateau and Middle Dam were combined and referred to as trap sites 1–3 to reflect their
relative proximity to exclosure Sites 1–3 and respective dung transects. Similarly, horse
captures at Boban Hut and Spion Kiope were referred to as trap sites 4–6 to reflect their
relative proximity to exclosure Sites 4–6 and associated dung transects.
Table 3.2 Protocol used to summarise the NSW NPWS trapping program so that trapping records could be compared with the dung transect results in Table 3.5.
Dung accumulation period Description of period Trap period dates Pre-July 2005 First 6 months of trapping April–September 2004 July 2005 (T1) Estimated 4-month dung November 2004–June 2005
accumulation period November 2005 (T2) First 4-month defined July–November 2005
dung accumulation period March 2006 (T3) Second 4-month defined December 2005–March 2006
dung accumulation period July 2006 (T4) Final 4-month defined April–July 2006
dung accumulation period Post-July 2006 4 months after dung August–November 2006 monitoring had ceased
Chapter 3. Indirect Effects on Macropods 58
The number of trap sites was dissimilar between trap site groupings and varied within
and between trapping periods. Thus, to standardise total horse captures, a
catch-per-unit-effort (CPUE) statistic was calculated using CPUE = G/E (Seber 1982), where
G was total horses captured and E, effort, was approximated as total trap months per trap
period. The CPUE was also an index of relative abundance (Forsyth et al. 2003; Tremblay et
al. 2009; Wiewel et al. 2009). The basic unit of effort was 1 trap month per trap site. Trap
sites with a trap paddock and steel trap yards operational at the same time (e.g. Wonga Flat)
were treated as one unit because trap paddocks were often used as holding paddocks for
horses captured in steel yards awaiting transport so the trap yard could be reset. The trap
paddock entrance was also adjacent to the trap yards and if trap yards contained a harem
group, the stallion deterred other horses. Otherwise, due to their design, trap paddocks
remained open continuously when a trap yard had been dismantled and were treated as one
unit. Trap paddocks were large fenced paddocks with a one-way funnel through which
horses can enter the paddock at any time, thus trap paddocks remained open continuously
whereas trap yards had to be cleared of horses and the trigger mechanism reset. Thus, if a
trapping period had multiple trap sites, E was calculated by summing the months that each
trap site was operational. Within a 1-month unit, the precise amount of time a trap was
open would have differed somewhat depending on the number of capture events and trap
program personnel. Despite these considerations, animal welfare criteria and a common
drive to justify contract or capture program expenditure ensured that captured horses were
removed and trap yards reset within a timeframe of days, and that lure feeding and the
checking of traps was reasonably frequent and comparable between contractors and NPWS
staff.
Captures of coacher mares and their foals were not included in horse capture
numbers. The two coacher mares on the Plateau were horses captured previously. They
were subsequently released to assist in the settling of other horses in trap yards or paddocks
as these horses were of a quiet disposition and had become semi-habituated to the presence
of humans.
Chapter 3. Indirect Effects on Macropods 59
3.2.2 Bobs Creek grazing exclusion experiment
In the Bobs Creek grazing exclusion experiment, the presence of herbivore dung was
assessed at the site and district scale. The exclosure experiment was replicated at ten sites in
Bobs Creek (Figure 3.7). At the site scale, three dung transects were marked permanently on
11–12 June 2006. Their location and orientation were chosen at random within 50 m of a
plot (Chapter 5).
Figure 3.7 Location of Bobs Creek grazing exclusion experiment exclosure sites relative to trap sites. The topography is shown using multispectral SPOT 5 imagery. The SPOT 5 image was captured on 26 May 2005; pixel resolution is 10 m (DNR 2005).
At the district scale, GIS software (ArcGIS v.9.1) was used to generate ten random
points for dung transects within a 4 × 1-km rectangular strip, 2 km either side of each site,
and 1-km wide along Bobs Creek tributary. In total, 100 dung transects were monitored in
April 2007, November 2007 and June 2008. Both site and district-scale transects were 50-
m long and dung deposits counted 5 m either side of the transect line in a quadrat of 0.05 ha.
The Paddys Plateau dung transect method was used for searching, identifying and counting
horse and kangaroo dung and clearing dung deposits.
Chapter 3. Indirect Effects on Macropods 60
Records were kept of all sightings of horses, cattle, macropods and other small
herbivores at the site scale. Details of horse and cattle mob composition and distinctive
markings of individuals were recorded and photographs taken if possible. Sites were
approached on foot stealthily and the riparian flat observed for several minutes from behind
cover for any herbivores and their location and numbers noted. Horses were commonly
encountered during area dung surveys and were not recorded as dung deposits were
deemed a more representative record of their activity. Other herbivores were rarely seen
and so a GPS location and description were taken of all sightings.
3.2.3 Landscape-scale survey of horse and non-horse catchments
A comparison of dung counts was made between two catchments occupied by
horses, Bobs Creek and Pargo Creek, and two catchments with no present or past history of
horses, Kangaroo Creek and Pantons Creek. Dung was recorded on 13 transects in each
catchment. Transects were stratified by topographic position in the landscape into hillslope
or spur, and were primarily used for landscape function analysis (LFA) in Chapter 6. While
the starting point was randomly chosen, the location of transects within the catchments
were stratified by a number of additional criteria relevant to LFA including aspect, slope and
vegetation community. As transects in horse and non-horse catchments were
environmentally equivalent (Chapter 6), the data were included in this chapter to examine
the extent of spatial separation between horses and macropods at catchment scale, that is
approximately the sum of the area of Bobs Creek and Pargo Creek (5000 ha) (Figure 6.4,
Chapter 6). Dung transects were 50 m long and dung deposits recorded 2 m either side of
the transect line in a quadrat of 0.02 ha. Dung transects were smaller than on Paddys
Plateau and in Bobs Creek due to the use of LFA gradsects as dung transects, where the focus
was on precise measurements of patch or interpatch length, width and composition, and the
ardeous terrain. At 2 m, rather than 5 m either side of the 50 m gradsect, I did not have to
deviate from the gradsect line while traversing steep slopes. Considerable time was also
spent locating environmentally equivalent gradsects, of which there were 52 in total, and
hence, 2 m was considered appropriate. The Paddys Plateau dung transect method was used
for searching, identifying and counting horse and kangaroo dung and clearing dung deposits.
Cattle dung was also counted. A single deposit corresponded to an intact cow pat. If not
explicitly stated, all dung deposits in this thesis are expressed as mean no. of deposits/ha.
Chapter 3. Indirect Effects on Macropods 61
3.2.4 Statistical analysis
3.2.4.1 Paddys Plateau district scale dung transects
At the Paddys Plateau district scale transects, the number of dung deposits (response
variable) was analysed separately for horse and macropods using a linear mixed-effects
model. Time was a fixed factor with four levels: July 2005 (T1), November 2005 (T2), March
2006 (T3), and July 2006 (T4). Habitat type (Habitat) was a fixed factor with four levels: GW
(n = 25), SW (n = 24), GS (n = 14), and T (n = 9). Transects were assigned to a Habitat after
data collection for the purpose of analysis so sample sizes were uneven. Due to the likely
variation in grazing pressure historically (possibly due to dams) and from horses during the
study as trapping effort at trap sites varied with time and with distance from Boban Hut, sites
were considered a fixed factor of interest with six corresponding levels. Site was included in
the model as exclosure site locations were used as a central reference point for stratifying
transects, although dung transects were random. As Transects were the sampling unit and
randomly selected, and Habitat had unequal sample sizes, the linear mixed-effects (lme)
function in R was appropriate. All univariate analyses in this thesis were undertaken in R
version 2.9.0 (Ihaka and Gentleman 1996). Patterns in Transect variability associated with
Site or Time were not evident in exploratory plots. A simple random effect attributed to
Transect was appropriate and converged in all analyses when the reliability of the lme
objects was checked using the intervals command in R (i.e. models were not ‘over-fitted’).
Model assumptions were checked with two diagnostic plots: (i) residuals versus fitted
responses to examine the assumption of equal variances and ensure that residuals did not
contain structure not accounted for in the model; and (ii) normal Q–Q plots to ensure the
residuals were normally distributed. Data violating these assumptions were transformed.
Horse dung counts were square-root-transformed. For macropod dung, counts were
log (X + 1)-transformed. As factors were unordered, planned post-hoc pair-wise comparisons
were made using the default Helmert contrast matrix (Venables and Ripley 2002). For single
factor linear models, the summary function in R provides pair-wise comparisons between the
baseline level and other levels. The relevel function was used to obtain comparisons
between all levels of Time.
Chapter 3. Indirect Effects on Macropods 62
3.2.4.2 Bobs Creek site scale and district scale dung transects
The response variable was the number of horse dung deposits as only horse dung
was sufficiently abundant to be analysed. To assess if the level of horse dung changed
throughout the experiment, a linear mixed-effects model was used for both the site and
district scale. The experimental design consisted of: (1) Time, a fixed factor with five (site
scale) and three (district scale) levels, and (2) Site, a random factor with ten levels. Model
assumptions were checked and pair-wise comparisons made using the same procedures as
for Paddys Plateau dung transects.
3.2.4.3 Landscape-scale survey of horse and non-horse catchments
The experimental design consisted of: (1) Treatment, a fixed factor with two levels,
horse versus non-horse; (2) Catchment, a random factor with four levels, Bobs Creek, Pargo
Creek, Kangaroo Creek and Pantons Creek; and (3) Stratum, a fixed or random factor with
two levels, hillslope versus spur. Initially, a linear mixed-effects model with Treatment and
Stratum as fixed effects and Catchment, and Stratum nested within Catchment, as random
effects was fitted. However, the interval predictions did not converge, suggesting the model
‘over-fitted’ the data. The same occurred with a simpler lme model with only Catchment as a
random effect. Therefore, the final model was a type of linear mixed-effects model called a
multistratum model (Venables and Ripley 2002 p. 285). Multistratum models occur where
there is more than one source of random variation in an experiment, as was the case for this
split-plot experiment (Heiberger 1989). The multistratum model for the landscape-scale
survey was based on Figure 3.8 (Venables and Ripley 2002 p. 282). The four Catchments
were treated as random blocks (Blocks I–IV). As only one Treatment level (e.g. horse) was
applied to each block, there were four blocks of two plots, one plot for horse and one for
non-horse (Figure 3.8). Each plot was divided into two subplots, with one level of Stratum
per subplot.
Chapter 3. Indirect Effects on Macropods 63
Figure 3.8 Split-plot design for the landscape-scale survey.
In multistratum models, the sample information and the model for the means of the
observations are partitioned into ‘strata’. To avoid confusion with the factor, Stratum, the
term ‘layer’ will be used hereafter in place of strata. The layers for the model used were:
(1) a 1-dimensional layer corresponding to the total of all observations; (2) a 3-dimensional
layer corresponding to comparisons between Treatment (or equivalent plot) totals within the
same block; and (3) a 48-dimensional layer corresponding to comparisons within plots. Such
types of models are fitted using the aov function in R, and are specified by a model formula
of the form (Venables and Ripley 2002): response ~ mean.formula + Error (layer.formula). In
this study, the response variables were the number of dung deposits for each herbivore and
the mean.formula included Treatment and Stratum. The layer.formula was Catchment,
specifying Layer 2. Layer 3 was included automatically as the ‘within’ layer. Information on
the Treatment main effect was available from Layer 2, with one degree of freedom for the
main effect and two residual degrees of freedom remaining. Information on the Stratum
main effect and the Treatment × Stratum interaction was only available from Layer 3, with
one degree of freedom each for the main effect and interaction and 46 residual degrees of
freedom. Model assumptions were checked using the same procedure as Paddys Plateau
dung transects. All herbivore dung counts were log-transformed. Post-hoc pair-wise
Chapter 3. Indirect Effects on Macropods 64
comparisons to discriminate between means for main effects were not necessary as there
were only two levels of Treatment, non-horse and horse, and two levels of Stratum, hillslope
and spur. For the interaction, planned post-hoc pair-wise comparisons were made using the
default Helmert contrast matrix (Venables and Ripley 2002).
3.2.4.4 Statistical significance defined for the thesis
Throughout this thesis a P-value ≤0.050 is considered statistically significant,
however, P-values ≤0.051–0.055 are also noted and discussed as mariginally significant and
of biological interest.
Chapter 3. Indirect Effects on Macropods 65
3.3 RESULTS
To reiterate, the number of deposits were all mean number of deposits/ha for Paddys
Plateau, Bobs Creek and the landscape-scale survey in horse and non-horse catchments in
Section 3.3.
3.3.1 Paddys Plateau district scale dung transects
3.3.1.1 Horse dung and habitat types
Horse dung deposits peaked across all habitat types in July 2005 (T1) and
subsequently declined to varying extents across habitat types, the Habitat × Time interaction
being significant (F9,144 = 3.14, P = 0.002; Table 3.3, Figure 3.9).
Horse dung declined in all habitat types between T1 and T2 with large proportional
reductions (%) in dung counts in most habitat types: GW (80.2%, P < 0.001), GS (59.5%,
P < 0.001), SW (50.2%, P < 0.001) and T (37.7%, P = 0.016) (Figure 3.9). Horse dung was less
in T2–T4 than T1 in all habitat types (P < 0.050). Dung changed little in GW and SW between
T2 and T4 but progressively declined in GS and T from T1> T2 > T3 = T4 in dung counts. The
additional 50.0% and 54.1% reductions in dung deposits in GS and T, respectively, between
T2 and T3 was significant for track (P = 0.050) and almost significant for grassy swale
(P = 0.076) (Figure 3.9). In both winter sampling times (T1 and T4), deposits were
significantly less in SW than all other habitat types (P < 0.050) except track in T4 when the
significance level was mariginal (P = 0.054), whereas in summer (T2) and early autumn (T3)
deposits were significantly greater in T than GW and SW (P ≤ 0.048). In summer, GS was
intermediate to T and the other habitat types, differing from GW (P = 0.002).
Chapter 3. Indirect Effects on Macropods 66
Figure 3.9 Mean (±1 S.E.) number of horse deposits/ha by Time and Habitat. Accumulation periods were July 2005 (T1), November 2005 (T2), March 2006 (T3), and July 2006 (T4) for the Habitat types grassy woodland (GW), shrubby woodland (SW), grassy swale (GS) and track (T). The text notation above the set of four bar columns for an accumulation period denotes significant differences between habitat types specific to that period (P ≤ 0.050). Significant differences between periods only refer to bar columns with an asterisk above the habitat type (P ≤ 0.050).
Table 3.3 Multifactor linear mixed-effects model output for horse and macropod dung deposits on dung transects. Numerator (Num) and denominator (Den) degrees of freedom (df).
Horse Macropod Source of variation Num df Den df F P F P Habitat 3 48 8.34 <0.001 5.37 0.003 Site 5 48 4.20 0.003 10.26 <0.001 Time 3 144 86.17 <0.001 31.08 <0.001 Habitat × Site 15 48 0.48 0.940 1.30 0.237 Habitat × Time 9 144 3.86 0.001 2.36 0.016 Site × Time 15 144 2.92 0.001 3.41 <0.001 Habitat × Site × Time 45 144 1.35 0.093 1.21 0.204
3.3.1.2 Macropod dung and habitat types
Over 90% of macropod dung was easily identified as eastern grey kangaroo. In
July 2005, macropod dung was rare and only recorded in SW and GS at an average of
≤7.5 deposits (Figure 3.10). After T2, macropod dung progressively increased across all
habitat types, moreso in GS, followed by GW and T. The Habitat × Time interaction was
significant (F9,144 = 2.36, P = 0.016; Table 3.3) with macropod dung greater in T2–T4 than T1 in
0
50
100
150
200
250
300
350
400
Hor
se d
epos
its
(no.
/ha)
GW SW GS T
*
*
T1 > T2, T3, T4 *
T3 < T2
July 2005 November 2005 March 2006 July 2006
GW, GS, T > SW
* *
T4 < T2
T > GW, SW
*
T > GW, SWGS > GW
GW, GS > SW
Chapter 3. Indirect Effects on Macropods 67
GW and GS (P ≤ 0.005). Incremental increases between T2 and T3 and between T3 and T4
were significant for GS (P ≤ 0.024) and for GW and SW between T3 and T4 only (P ≤ 0.013).
The increase in macropod dung in track between T3 and T4 differed from T1 (P = 0.005).
Habitat type differences were consistent, with greater macropod dung in GS than SW and T
at T2–T4 (P ≤ 0.048) and GW intermediate and greater than SW at T3 and T4 (P ≤ 0.042).
Figure 3.10 Mean (±1 S.E.) number of macropod deposits/ha by Time and Habitat. Notation as for Figure 3.9 except for July 2006 within habitat type time differences, where the notation directly above the track bar graph referred to track only and the notation spanning the first three bars referred to GW, GS and SW. 3.3.1.3 Horse dung and site differences
In July 2005, transects had an average of ≥161.7 horse deposits across all sites. The
Site × Time interaction was significant (F15,144 = 2.92, P = 0.001; Table 3.3) as horse dung
declined in sites at different times through the course of the experiment (Figure 3.11). Dung
temporarily declined in Site 5 between T2 and T3, differing from counts at T1 and T2
(P < 0.001). Otherwise, sampling times did not differ and dung was greater in Site 5 than all
other sites at T2 and T4. Conversely, dung deposits ‘crashed’ to a mean of ≤50.0 deposits in
Sites 1–4 and Site 6 sometime after T1 (Figure 3.11). The response was immediate in Site 1
and Site 2 and occurred between T1 and T2 (P < 0.001), whereas declines were progressive in
Sites 3, 4 and 6. Dung declined to ≤50.0 deposits in Site 3 between T2 and T3 (P < 0.001) and
0
20
40
60
80
100
120
140
160
180
200
Mac
ropo
d de
posi
ts (
no./
ha)
GW SW GS T
*
T1 < T2, T3, T4
*
*GS > GW, SW, TGW > SW
GS > SW, TGW > SW
July 2005 November 2005 March 2006 July 2006
*
*
T3 > T2
*
GS > SW, T
T4 > T3
*T4 > T1
Chapter 3. Indirect Effects on Macropods 68
Sites 4 and 6 between T3 and T4. Horse dung was less at T2–T4 than T1 in all sites except
Site 5 (P ≤ 0.001).
Figure 3.11 Mean (±1 S.E.) number of horse deposits/ha by Time and Site. Times: July 2005 (T1), November 2005 (T2), March 2006 (T3) and July 2006 (T4), Sites: Site 1 (S1)–Site 6 (S6). The text notation above the set of six bar columns for an accumulation period denotes significant differences between sites specific to that period (P < 0.050). Significant differences between periods expressed in the text notation only applys to sites with an asterisk above the bar column (P < 0.050).
3.3.1.4 Macropod dung and site differences
The Site × Time interaction was significant (F15,144 = 3.41, P < 0.001; Table 3.3) as
macropod dung increased in sites at different times through the course of the experiment
(Figure 3.12). In July 2005 (T1), macropod dung was only recorded in Site 1 (a total of
11 deposits across three transects). In November 2005 (T2), macropod dung was recorded
in Sites 1–4 with an average of 1.7–23.3 deposits across sites. Dung increased to 116.7 and
53.3 deposits, respectively, in Site 1 (P < 0.001) and Site 2 (P = 0.050) during the March 2006
accumulation period, and to 181.7 (P = 0.042) and 83.3 deposits, respectively, in July 2006.
Dung was significantly greater in Site 1 than other sites by 64.2–116.8 deposits in
March 2006 and July 2006 (P < 0.050).
Dung only significantly increased in Site 3 (to a mean of 60.0 deposits) and Site 4 (to a
mean of 110 deposits) during the July 2006 accumulation period (P < 0.050). In July 2006,
dung was also greater in Sites 2–4 than Site 5 and Site 6. No macropod dung was recorded in
0
50
100
150
200
250
300
350H
orse
dep
osit
s (n
o./h
a)
1 2 3 4 5 6
July 2005 November 2005 March 2006 July 2006
*
S5 > S(1, 2, 3, 4, 6)
S5 > S(1, 2, 3, 4, 6)*
*
*
*
T1 > T2, T3, T4
*
T2 > T3
*
T3 < T1, T2
Chapter 3. Indirect Effects on Macropods 69
Site 5 and Site 6 until July 2006 when the total of a single deposit of kangaroo dung was
found in Site 5 and a total of 6 deposits across two transects in Site 6.
Figure 3.12 Mean (±1 S.E.) number of macropod deposits/ha for Time by Site. Notation as for Figure 3.11.
3.3.2 Horse capture and removal data for Paddys Plateau
The NSW NPWS trapping program results were summarised to show when trap sites
were operational and the number of horses trapped (Table 3.4). The term ‘trapped’ refers to
the capture and removal of horses from the Park. Months not shown were when the
program was halted and no trap sites were operational. Opportunistic lure feeding by NSW
NPWS field staff continued throughout. A trap month was when a site was operational, that
is, the trap contained feed and was set to capture horses. Alternatively, the trap held
trapped horses waiting to be transferred to a holding paddock or transported off-park, after
which the trap was re-set.
The number of horses trapped was greater in the first 2 trap months of each year of
the program, or the first 2 trap months that a trap site was in operation in any given year
(Table 3.4). In 2004, 113 horses were trapped over 13 trap months. In 2005 and 2006, the
number of horses trapped per year declined despite an increase in trap months to 21 months
and 17 months.
0
50
100
150
200
250
300M
acro
pod
depo
sits
(no
./ha
)1 2 3 4 5 6
July 2005 November 2005 March 2006 July 2006
S1 > S(2, 3, 4, 5, 6)
S1 > S(2, 3, 4, 5, 6)S2, S3, S4 > S5, S6
*T3 > T1, T2
*T3 > T1
*T4 > T(1, 2, 3)
*
T4 > T1, T2
*T4 > T(1, 2, 3)
*
T4 > T1, T2
Chapter 3. Indirect Effects on Macropods 70
Table 3.4 Number of horses trapped on Paddys Plateau in each trap month and year of the trapping program. TY: Trap yard, TP: Trap Paddock, LF: Lure feeding only; '–' indicated a trap site was ‘closed’ whereas a 0 referred to no horse captures in an operational trap yard or paddock. Total numbers of horse captures for each year are italicised.
2004 Trap area April May July August September November Area totals Wonga Flat (TY, TP) 29 13 3 1 2 4 52 Perrys Yards (TY) 1 0 5 5 1 - 12 Boban Hut (TY, TP) - - LF LF 10 39 49 Monthly Totals 30 13 8 6 13 43 113
2005
Trap area May June September October November December Area totals
Wonga Flat (TY, TP) 5 12 0 3 3 0 23 Perrys Yards (TY) 4 0 0 1 1 1 7 Ryans Paddock (TP) - - LF LF 5 0 5 Boban Hut (TY, TP) 8 16 2 3 9 - 38 Spion Kiope (TY) - LF LF 2 1 - 3 Monthly Totals 17 28 2 9 19 1 76
2006
Trap area April June August September October November Area totals
Wonga Flat (TP) 0 1 0 0 - - 1 Mt Gardiner Plateau (TY) 10 0 - - - - 10 Perrys Yards (TY) LF 1 0 - - - 1 Ryans Paddock (TP) LF LF 4 0 - - 4 Middle Dam (TY, TP) 6 0 3 0 TP only TP only 9 Boban Hut (TY, TP) - LF LF 12 7 8 27 Monthly Totals 16 2 7 12 7 8 52
2007 Trap area February March Area totals Ryans Paddock (TP) 0 2 2 Boban Hut (TY, TP) 6 8 14 Monthly Totals 6 10 16
Chapter 3. Indirect Effects on Macropods 71
3.3.2.1 Trap sites 1–3
CPUE values tended to decline as the trap programs progressed in time, with the first
two trap periods (T1–T2) capturing most horses (6.00 and 5.25 horses/month), respectively
(Table 3.5). After November 2005 (T2), horse captures were low (≤1.71 horses/month)
except in July 2006 (T4). In the July 2006 trap period, almost all (16) of the 18 horses were
captured in April 2006 (Table 3.4). This was the first month that the trapping program
resumed in 2006 after the 3-month summer break, with lure feeding commencing in
February 2006. Capture comments for most horses caught during T1 and T2 mentioned
prior sightings or that the horses were known on Paddys Plateau, but the April 2006 captures
appeared to be recent immigrants. A mob of ten horses was captured at Mt Gardiner
Plateau trap site and after no horses were captured in the following trap month, the trap site
was closed (Table 3.4). It was not re-opened for the duration of this study as there was no
further build-up of mobs in the Mt Gardiner and Wonga Flat region. The other trap site was
Middle Dam, and as trapping in subsequent months caught few horses the trap yards were
permanently closed (Table 3.4). While the trap paddock remained open for a further
2 months, no horses were captured (Table 3.5). The increase in the CPUE to
2.57 horses/month in July 2006 was due to the Mt Gardiner and Middle Dam captures in
April 2006 and few horses were captured in the remaining 5 trap months in 2006. The CPUE
of 0.78 horses/month for the Post-July 2006 trap period was low compared to the first three
trap periods (Table 3.5).
Table 3.5 Summary of trap data from the NSW NPWS capture and removal programs. No. of trap sites included trap sites in operation for at least 1 trap month. CPUE: catch-per-unit-effort, No.: number. '—' indicated trap site closed.
Total No. of Total trap CPUE Trapping period horses trap sites months TRAP SITES 1–3 Pre-July 2005 60 2 10 6.00 July 2005 (T1) 21 2 4 5.25 November 2005 (T2) 12 2 to 3 7 1.71 March 2006 (T3) 1 3 3 0.00 July 2006 (T4) 18 3 to 4 7 2.57 Post-July 2006 7 1 to 4 9 0.78 TRAP SITES 4–6 Pre-July 2005 10 1 1 10.00 July 2005 (T1) 23 1 2 11.50 November 2005 (T2) 18 1 to 2 5 3.60 March 2006 (T3) — — — — July 2006 (T4) — — — — Post-July 2006 27 1 3 9.00
Chapter 3. Indirect Effects on Macropods 72
3.3.2.2 Trap sites 4–6
CPUE values tended to fluctuate according to the intensity of the preceding trap
period (Table 3.5). Additional factors were immigration, the late start of the capture
program at Boban Hut and Spion Kiope, the smaller number of trap sites, and the greater
frequency of trap closures, and the continuation of the program at Boban Hut in 2006 and
2007 after all but one trap site had been permanently closed at trap sites 1–3 by
September 2006 (Table 3.4).
The Pre-July 2005 capture period encompassed only the first trap month,
September 2004, at Boban Hut (Table 3.5), when ten horses were captured (Table 3.4). The
CPUE for the subsequent trap period, July 2005 (T1), was 11.50 horses/month (Table 3.5).
The pattern for trap sites 1–3 was repeated at trap sites 4–6 in that the CPUE was
comparatively low (3.60 horses/month) in the November 2005 (T2) trap period compared to
the previous two trap periods, although 2.2 times greater than the corresponding CPUE for
trap sites 1–3. Trap sites 4–6 were closed for the March 2006 (T3) and July 2006 (T4) trap
periods. This may explain the Post-July 2006 value of 9.00 horses/month.
3.3.3 Bobs Creek site scale and district scale dung transects
3.3.3.1 Dung transects
Only horse dung was recorded on dung transects at the site scale (Figure 3.13a) with
an average of approximately 158.7–241.3 deposits across the five sampling times. The Time
main effect was marginally significant (F4,136 = 2.39, P = 0.054). Pair-wise comparisons were
only significant between the first sampling time (241.3 deposits), when the accumulation
period was undefined, and November 2007 (170.7 deposits, P = 0.018) and June 2008
(158.7 deposits, P = 0.006).
District-wide, judging by their dung, horses were the most consistent and abundant
mammalian herbivore within a 4 × 1-km area of sites, whereas cattle and macropods were
rare (Figure 3.13b). To illustrate, in April 2007, 96% of transects recorded horse dung, while
only 2% (2 transects) recorded one macropod dung deposit per transect and the transect
where the mob of four cattle was sighted contained six cattle deposits. Thus, overall,
1033 horse deposits were recorded compared to two macropod and six cattle deposits in
that month. In November 2007 and June 2008, 91% and 87% of transects had horse dung
whereas no macropod or cattle dung was recorded. The Time main effect was significant
(F2,288 = 8.84, P < 0.001). The mean number of horse deposits was significantly lower in
Chapter 3. Indirect Effects on Macropods 73
November 2007 (P = 0.001) and June 2008 (P = 0.002) than April 2007, as dung had
accumulated over an undefined period at the first sampling time and at the second and final
sampling times the accumulation period was limited to 8 and 9 months respectively. Horse
dung abundance did not differ between the two defined accumulation periods (P = 0.386).
Figure 3.13 Mean (±1 S.E.) number of horse deposits/ha recorded from (a) 30 dung transects at the site scale for horses only, where * denotes a significant difference (P < 0.050) between Time 1 (T1, June 2006) and both Time 3 (T3, November 2007) and Time 5 (T5, June 2008) and (b) 100 transects at the district scale for the three herbivores, where * denotes a significant difference (P < 0.050) between Time 1 (T1, April 2007) and both Time 2 (T2, November 2007) and Time 3 (T3, June 2008).
3.3.3.2 Herbivore sightings
Sightings were consistent with site scale dung transects as horses were the only large
herbivores observed grazing the flats (Table 3.6). At least one horse or horse mob was seen
on all but 1 day during the first two sampling times, and then every day for the remaining
three sampling times. Some mobs were seen repeatedly. Multiple sightings of horses were
recorded at each site and the number of horses ranged from a single individual to 12 adults
and four juveniles, which appeared to be three separate mobs grazing together. Otherwise,
just the one brown hare and no cattle or macropods were observed in sites (Table 3.6). A
mob of four cattle was observed on 17 April 2007. However, the mob was 3 km downstream
of Site 1 beyond the study area (site numbers progressed upstream).
0
50
100
150
200
250
300
Ho
rse
de
po
sits
(n
o./
ha)
Apr-07 Nov-07 Feb-08 Jun-08Jun-06
a)
*
T1 > T3, T5
0
50
100
150
200
250
April 2007 November 2007
June 2008
Dun
g de
posi
ts (
no./
ha)
HorseMacropodCattle
b)
*
T1 > T2, T3
Chapter 3. Indirect Effects on Macropods 74
Table 3.6 Herbivore sightings at riparian exclosure sites. ‘Visitation days’ were the number of days that the riparian exclosures were monitored. Sighting events were the number of times that horses were observed grazing control plots or sites.
Jun-06 Apr-07 Nov-07 Feb-08 Jun-08
No. of visitation days 6 7 7 6 7 No. of horse sighting events 5 6 9 6 7 Sighting events/visitation days 0.83 0.86 1.29 1.00 1.00 No. of horses seen 24 26 31 34 25 No. of cattle seen 0 0 0 0 0 No. of macropods seen 0 0 0 0 0 No. of rabbits/hares seen 0 0 1 0 0
3.3.3.3 Horse capture and removal data
Ballards Flat was the only trap site operational in 2006, and a total of 29 horses were
captured in 4 months in 2006 and 45 horses in 2007 (Table 3.7). Deep Water trap site was
first operational in June 2007 when seven horses were captured. In 2008, Ballards Flat and
Deep Water were operational in February and April, with respective totals of ten and
12 horses in those 2 months. Deep Hole and Pargo were operational in May and June 2008
with a total of eight horses captured at each trap site.
Table 3.7 Total number of horses trapped at four trap sites in or adjacent to Bobs Creek catchment during 2006–2008. And '–' indicates that the trap site was closed.
2006 2007 2008 May, June, February, March, February, April,
Trap yard site September and October June and July May and June Ballards Flat 29 45 10 Deep Water – 7 12 Deep Hole – – 8 Pargo – – 8 Yearly totals 29 52 38 Horses in total 119
3.3.4 Landscape-scale survey of horse and non-horse catchments
3.3.4.1 Horse dung
In horse catchments (Bobs and Pargo Creek), horse deposits were recorded on all
26 dung transects, and the presence of horses confirmed by frequent sightings and other
indirect signs such as hoof prints. Horse dung averaged 532.7 ± 71.7 deposits and the
amount of horse dung on slopes and spurs did not differ as the Stratum main effect was not
significant (F1,46 = 0.32, P = 0.570; Table 3.8, Figure 3.14a). In non-horse catchments
Chapter 3. Indirect Effects on Macropods 75
(Kangaroo and Pantons Creek), no horse deposits were recorded on transects, nor were any
signs of horses observed. Hence, the difference in mean dung deposit counts between horse
and non-horse catchments and the Treatment main effect was highly significant (F1,2 = 2138,
P < 0.001; Table 3.8).
3.3.4.2 Macropod dung
The opposite trend was recorded for macropod dung. Only a single dung deposit was
recorded on three transects in horse catchments, whereas single to multiple macropod dung
deposits were recorded at all 26 transects in non-horse catchments. The mean number of
macropod dung deposits in non-horse catchments (551.9 ± 92.1 deposits) was 91% greater
than in horse catchments (48.1 ± 16.8 deposits). The Treatment × Stratum interaction was
significant (F1,46 = 11.58, P = 0.001; Table 3.8) because in horse catchments, macropod dung
deposits were more abundant on spurs than hillslopes, whereas in non-horse catchments
there was more macropod dung on hillslopes than spurs (Figure 3.14b).
Figure 3.14 Mean (±1 S.E.) number of deposits/ha of (a) horse and (b) macropod dung on hillslopes and spurs in horse and non-horse catchments. Table 3.8 Multifactor ANOVA corresponding to the mean (±1 S.E.) number of herbivore dung deposits/ha on hillslopes and spurs in horse and non-horse catchments. Mac.: Macropod, Treat.:Treatment.
Horse catchments Non-horse catchments Source of variation (P-values) Treatment
Slope Spur Slope Spur Treat. Stratum × Stratum Horse 539.3 ± 125.6 525.0 ± 59.5 0.0 ± 0.0 0.0 ± 0.0 0.000 0.570 0.570 Mac. 10.7 ± 5.7 91.7 ± 31.8 582.1 ± 110.1 516.7 ± 157.6 0.160 0.570 0.001 Cattle 0.0 ± 0.0 0.0 ± 0.0 14.3 ± 11.0 125.0 ± 55.2 0.007 0.049 0.049
0
200
400
600
800
1000
Bobs Pargo Kangaroo Pantons
Hor
se d
epos
its
(no.
/ha)
Slope
Spur
Horse Non-horse
a)
0
200
400
600
800
1000
1200
Bobs Kangaroo
Mac
ropo
d de
posi
ts (
no./
ha)
Slope
Spur
Horse Non-horse
b)
Pargo Pantons
Chapter 3. Indirect Effects on Macropods 76
3.3.4.3 Cattle dung Cattle dung was present on seven of the 26 transects in non-horse catchments with
an average of 65.4 ± 27.8 dung deposits, whereas there was no cattle dung in horse
catchments (Figure 3.15). The Treatment × Stratum interaction was significant
(F1,46 = 4.08, P = 0.049; Table 3.8), with the majority of cattle dung recorded on spurs and
little dung on hillslopes in non-horse catchments.
Figure 3.15 Mean (±1 S.E.) number of cattle dung deposits/ha on hillslopes and spurs in horse and non-horse catchments.
0
40
80
120
160
200
Bobs Pargo Kangaroo Pantons
Catt
le d
epos
its
(no.
/ha)
Slope
Spur
Horse Non-horse
Chapter 3. Indirect Effects on Macropods 77
3.4 DISCUSSION
The Paddys Plateau dung transects indicated that horses displaced macropods and
probably deterred them from utilising forage resources at the district scale (100 ha). At four
of the six sites, as horse deposits declined, the number of macropod deposits increased until
macropod dung was more prevalent than horse dung. Importantly, the trend was staggered
across sites depending on their relative proximity to trap locations and how quickly, and to
what level, horse dung declined. Trends in catch-per-unit-effort (CPUE) values reinforced
patterns in dung transect counts and supported the argument that macropods were
responding to changes in the abundance of horses, rather than the removal of horses simply
coinciding with an increase in macropod numbers or activity.
When dung transects were established in July 2005 (T1) peak levels of horse dung in
all sites did not differ whereas macropod dung was rare and restricted to Site 1 (total of
11 deposits across all transects). The CPUE of 5.25 horses/month calculated for trap sites 1–
3 over the 4 months prior to July 2005 was not much lower than the 6.00 horses/month
estimated for the first 6 months of the trapping program, suggesting peak horse deposits in
July 2005 reflected a high abundance of horses rather than over-estimation due to the
unrestricted accumulation period. After July 2005, horse dung consistently declined in all
sites except Site 5. The response was abrupt in Sites 1 and 2, with mean deposits decreasing
by 88.0% and 82.1%, respectively, to ≤33.3 deposits/ha between July 2005 (T1) and
November 2005 (T2). Over the same period, CPUE values at both trap sites 1–3 and 4–6
declined by two-thirds and macropod dung increased at Sites 1–4 to an average
of 23.3 deposits/ha or less. The summary of demographic data in the trapping program
(Appendix 3) suggested that the presence of horse dung in Sites 1 and 2 was a result of
transitory rather than long-term resident horse activity, and associated horse dung levels of
≤40.0 deposits/ha were termed ‘nominal’ dung levels to reflect demographic data. Over the
subsequent accumulation period (between T2 and T3), trap sites 1–3 were in operation for
3 trap months but no horses were trapped. In the absence of horses, macropod dung
increased by 80.1% in Site 1 and 75.4% in Site 2 so that macropod dung was more prevalent
than horse dung by 86.3 and 34.7 deposits/ha, respectively. The pattern in Sites 1 and 2 of
horse dung declining to nominal levels and macropod dung increasing over the following
accumulation period and continuing to increase was progressively repeated, first at Site 3,
then Sites 4 and 6. CPUE values for trap sites 1–3 also remained low during the course of the
experiment. After June 2005, zero or one horse was captured per month in most trap
Chapter 3. Indirect Effects on Macropods 78
months and trap sites associated with sites 1–3 (e.g. Wonga Flat and Perrys Yard) prompting
the permanent closure of trap sites 1–3 after June 2006. CPUE values for trap sites 4–6
were consistently at least twice that at trap sites 1–3 and while not in operation during the
last two dung accumulation periods, the Post-July 2006 CPUE (9.0 horses/month) was almost
as high as the first two capture periods. The CPUE for trap sites 1–3 (0.78 horses/month) was
low at this time. This difference may explain why horse dung decreased at Sites 3, 4 and 6
later than in Sites 1 and 2, which were closest to trap sites 1–3, and the greater number of
horse deposits in Site 5 (mean of 112.0 deposits/ha), adjacent to the primary trap site, Boban
Hut, at the final accumulation period (July 2006). As a result, only one macropod dung
deposit was ever detected on Site 5 transects. Patterns for horse dung at Site 6 resembled
Site 4 in that horse dung was low (50.0 deposits/ha) by the final accumulation period, but
macropod dung did not increase. The proximity of Site 6 to Boban Hut may have continued
to deter macropods. Site 4 exclosures were closer to Boban Hut than the Site 6 exclosures,
but Site 4 dung transects were located south towards the Combolo catchment border. Dung
transects in Sites 5 and 6 were located north of exclosures and adjacent to the Bobs Creek
catchment ridgeline that served as a movement route from the Sara River flats. Therefore,
by the final accumulation period horse dung had declined in Sites 1–4 from 161.7–
255.0 deposits/ha in July 2005 to ≤40.0 deposits/ha, whereas macropod dung had
significantly increased from almost nothing to 60.0–181.7 deposits/ha in response to the low
abundance of horses.
The inverse relationship between horse and macropod dung was strongest in habitat
types thought to be prime grazing areas for both herbivores. The majority of macropod dung
detected in March 2006 was in grassy swales and grassy woodlands. In the final
accumulation period, macropod dung was greatest in grassy swales (134.3 deposits/ha)
followed by grassy woodlands (88.0 deposits/ha), and although both habitats registered
more dung than shrubby woodland, only grassy swale differed from track. The order of
habitat types from greatest to least number of dung deposits for macropods in March and
July 2006 mirrored that for horses in July 2005, confirming a high degree of overlap in habitat
preferences between the species. In the final accumulation period macropod deposits in
shrubby woodland also increased by 71.0%, accompanied by a substantial increase in track
transects (63.6%). Macropods appeared to expand their use of Paddys Plateau over time as
progressively more horses were removed and, by the final accumulation period, macropod
dung was also significantly greater in more marginal habitat types. Given the result for
Chapter 3. Indirect Effects on Macropods 79
grassy swales, in particular, the relative difference in the proportion of transects in grassy
swales may partly explain why the response of macropods was greater in Site 1 (0.25) than
Site 2 (0.17) and in Site 4 (0.25) than Site 3 (0.08). In addition, while Site 1 had significantly
more macropod dung than other sites in March and July 2006, it was also the only site to
have some macropod dung during the first accumulation period. Macropods were well
established in the south-eastern section of Paddys Plateau near Mt Wonga and Tallagandra
Depot. This area of the Park either borders large grazing properties or contains small parcels
of fenced paddocks privately owned or leased which are used for grazing cattle. Hence, the
rapid colonisation of areas by macropods once horses were no longer present was not
surprising.
The pattern on Paddys Plateau was not repeated in Bobs Creek. The horse dung
counts and the trapping data suggested that this was because, unlike the Plateau, the
relative abundance of horses in Bobs Creek did not decline during the study. No macropod
dung was recorded at the site scale (0.01 ha) and just two deposits in total were recorded
district-wide (4 × 1 km), compared to an average of at least 160.0 horse deposits/ha at both
scales. Except for the baseline horse dung counts when the accumulation period was
potentially as long as the time to decay, mean horse deposits at the site and district scale did
not decline significantly through time. Horses were consistently sighted in similar frequency
and numbers grazing the Bobs Creek riparian flats and while monitoring regional dung
transects. The density of horses is thought to be greatest in Bobs Creek, followed by Pargo
Creek and the Sara River (Chapter 2). Yet in the first year of trapping on Paddys Plateau,
almost the same number of horses were trapped (113 horses in 2004) as the total number of
horses trapped along the Sara River in 2 years (119 horses). If the NPWS continue to remove
horses and in numbers greater than the annual population growth rate, it may take longer
for macropods to colonise Bobs Creek than Paddys Plateau since Bobs Creek is not
surrounded by a reserve population of macropods sustained by pastoral lands. The absence
of macropod dung was not due to lack of suitable habitat for macropods. At least five
species of macropod have been sighted historically in the Sara River, Bobs Creek and Pargo
Creek catchments (NSW NPWS 2009a), and macropods were observed in unprecedented
numbers after the October 2000 cull on the Sara River flats (Olsen and Low 2006). The
presence of macropod dung on all transects in non-horse catchments (Kangaroo and Pantons
Creek), with an average of 551.9 ± 92.1 deposits/ha would appear to support that
assessment, as the locations of transects were environmentally matched with those in horse
Chapter 3. Indirect Effects on Macropods 80
catchments (Bobs and Pargo Creek). Consistent with the Bobs Creek exclosure transects, just
the single macropod deposit was recorded on three individual transects of the 12 transects in
Bobs Creek catchment. Levels of macropod dung were low in Pargo Creek in comparison to
non-horse catchments, but more prevalent than in Bobs Creek, ranging from 1.0–7.0 deposits
per transect across eight transects. Fewer horses have historically been recorded from aerial
surveys in Pargo Creek compared to Bobs Creek (Chapter 2). Pargo Creek thus drove the
response of macropods in horse catchments, where macropods appeared to change their use
of hillslopes and spurs in the presence of horses. In non-horse catchments, macropod dung
tended to occur more on hillslopes than spurs, while the opposite was true in horse
catchments. The lack of dung on hillslopes in horse catchments suggests that macropods do
not forage in horse catchments, and perhaps only use spurs occasionally when travelling
through. GFRNP is considered a control comparison for wild dog control programs in other
national parks in the region (e.g. Oxley Wild Rivers National Park, Guy Ballard, I&I
pers. comm.) as the wild dog population is not controlled or managed in any area of the Park
(S. Leathers pers. comm.). Thus, wild dog control would not have influenced macropod or
horse distribution throughout this study.
What remains unknown is the mechanism underlying the evident dissociation
between horses and macropods, both at the smaller site scale and broader catchment scale.
Fankhauser et al. (2008) questioned a perceived propensity to explain the segregation of
livestock and native herbivores as exploitative competition (e.g. Newsome 1971; Caughley
1987; Wilson 1991b) without also considering ultimate reasons, such as the need for native
species to avoid transmission of disease or gastrointestinal parasites via dung. A possible
exception is Andrew and Lange (1986), who suggested kangaroos and sheep dissociated in
their study because kangaroos selected pastures that were ungrazed by sheep or because
sheep disturbed sites had become fouled in some way (e.g. excessive dung). Eastern grey
kangaroos have been found to avoid the dung of conspecifics by moving through patches
contaminated with gastrointestinal parasite larvae as encountered, remaining longer in
uncontaminated patches, rather than actively selecting less contaminated patches (Garnick
et al. 2009). This response was consistent with that of Ramp and Coulson (2002, 2004), who
found that eastern grey kangaroos made foraging decisions at the habitat scale, with no
evidence of patch choice. The eastern grey kangaroos in Garnick et al. (2009) were unable to
discriminate between parasite-infected and parasite-free dung and did not adjust their
foraging behaviour in response to variation in the density of parasite larvae. Thus, they
Chapter 3. Indirect Effects on Macropods 81
evaded contaminated patches in general to avoid contacting larvae, as 95% of larvae is often
found <1 m of domestic horse and other ungulate dung (Sykes 1987; Fleurance et al. 2005;
Fleurance et al. 2007). As the main argument for dung avoidance is that it reduces exposure
to gastrointestinal parasite larvae (e.g. nematodes), for dung avoidance to apply to this
study, horses and eastern grey kangaroos on Paddys Plateau should be infected by some of
the same species of intestinal parasites (Sarah Garnick, pers. comm.), which is unknown at
this stage. Interspecific dung avoidance has rarely been addressed and is not well
understood (Benham and Broom 1991; Aoyama et al. 1994; Daniels et al. 2001; Fankhauser
et al. 2008) and cannot be immediately ruled out as a mechanism of avoidance on Paddys
Plateau. However, given the limited evidence available at this stage, an initial analysis of the
degree of overlap in parasite species between horse and eastern grey kangaroo dung is
essential before a manipulative behavioural and field experiment is considered.
Exploitative or interference competition was equally plausible. Overlap in habitat
preferences and diet was evident in dung counts and biomass results (Chapter 4), but
preferences and feeding strategies are also important in exploitative competition. In
environments most compatible with GFRNP, horses have the same feeding strategy as
eastern grey kangaroos in Australia’s temperate grasslands (Chapter 1). Both species are
true grazers feeding predominantly on grasses and respond to quality over quantity by
selectively spending more time feeding in areas with a greater density of green plant tissue
(Salter and Hudson 1979; Hill 1982; Duncan 1983; Taylor 1984; Duncan 1992; Crane et al.
1997a; Linklater et al. 2000). In addition, unlike cattle who lack top incisors, horses have
both top and bottom incisors and a more elongate head and flexible lips (Rook et al. 2004).
This enables them to trim vegetation close to the ground and then regraze the high quality
soft, short green shoots when they sprout from the crown (Menard et al. 2002; Lamoot et al.
2005). Horses feed on grass too short for cattle in at least two European grazing systems
(Gordon 1989). Thus, both horses and eastern greys exhibit a preference for and ability to
utilise short swards or grazing lawns based on nutritional value (Hill 1982; Rogers 1991;
Landsberg and Stol 1996). This would explain the apparent contradiction with studies where
eastern grey kangaroos selectively foraged closer to cattle in their near (<100 m) and broad
distributions (Hill 1982; Payne and Jarman 1999; Ritchie et al. 2009) to access the higher
quality ‘green pick’ exposed when cattle reduce the biomass of dry, perennial grasses (Frith
1970; Newsome 1971, 1975).
Chapter 3. Indirect Effects on Macropods 82
While overlap in resource use highlights the possibility for competition, interspecific
competition can only occur if resources are limiting to at least one of the species with
resultant demographic consequences for one or both species (Schoener 1983; Wiens 1989;
Putman 1996). On Paddys Plateau, grassy swale and grassy woodland habitats were
common and well dispersed, and biomass did not appear to be limiting (Chapter 4) even
when horses were relatively abundant. When macropod dung was still rare on dung
transects at June and December 2005, biomass in exclosures was above 100 g/m2 across all
sites. In determining the functional response of red kangaroos (Macropus rufus) in the semi-
arid zone, Short (1985) predicted the species only became food limited at a vegetation
biomass of 25–30 g/m2. Manipulative field experiments have concurred with this prediction.
Exploitative competition between large kangaroos and domestic sheep first became
apparent at a total pasture biomass of 40–50 g/m2 or in comparative dry years (Andrew and
Lange 1986; Wilson 1991a, 1991b; Norbury and Norbury 1993; Edwards et al. 1996),
although the evidence for exploitative competition was equivocal (Squires 1982; Edwards
1989; Payne and Jarman 1999 for a review). Short’s model has also been applied to
interactions between eastern grey kangaroos and other native wildlife, and an average
biomass of more than 100 g/m2 was considered sufficient to rule out exploitative
competition (Woolnough and Johnson 2000). On that basis, the potential for exploitative
competition would be greater for the riparian flats along Bobs Creek tributary considering
biomass in spring was as low as 45 g/m2 (Chapter 5) and the flats are small in size and rare in
the catchment. Fletcher (2006) recently examined the functional response of eastern grey
kangaroos in temperate kangaroo grass-dominated grasslands. A number of functional
responses were plausible, including Short’s model for red kangaroos, however, there was
also evidence of satiation of eastern grey kangaroos requiring high herbage mass
(>600 g/m2), which should be investigated further before exploitative competition is
dismissed for Paddys Plateau.
The final explanation presumes the existence of a social dominance hierarchy where
as subordinates, macropods altered their foraging behaviour in response to the direct
presence or threat of horses (Van Kreveld 1970; Beilharz and Zeeb 1982; Drews 1993).
Dominance hierarchies may be intrinsically determined (French and Smith 2005), but
generally arise out of interference competition (Fellers 1987; Savolainen and Vepsalainen
1989), where body size and mass or relative number of individuals determine interspecific
rank (Fisler 1977; Shelley et al. 2004). Mob size and dynamics of horses and eastern grey
Chapter 3. Indirect Effects on Macropods 83
kangaroos are comparable (Kaufmann 1975; Taylor 1982; Jarman and Coulson 1989; Linklater
2000), but the body size and weight of horses is greater by an order of magnitude (Dawson
1995; Fletcher 2006; Csurhes et al. 2009). Smaller species rarely dominate larger species
(Morse 1974). In the North American rangelands, feral horses are subordinate only to bison
(Bison bison) and dominant over numerous herbivores including cattle (Bos taurus) and
desert bighorn sheep (Berger 1986; Coates and Schemnitz 1994; Mosley 1999). Feral horses
have been observed to directly interfere with subordinate Great Basin Desert ungulates
(Berger 1985) and cattle with red kangaroos and eastern grey kangaroos (Kaufmann 1975;
Croft 1980; Payne and Jarman 1999). Aggressive acts are uncommon, as once the dominance
hierarchy is established, interspecific social competition largely becomes a passive process
(Mosley 1999). When resources are adequate across the landscape, but not to the extent
that animals can ignore each other’s presence, the subordinate species usually adjust their
spatial relationships relative to dominant animals to avoid conflict (Mosley 1999). Desert
bighorn sheep, for example, have been observed to never to use a watering point at the
same time as feral horses, nor when feral horses were within sight of the watering point, and
can wait hours for feral burros to leave a water source before approaching for a drink (Dunn
and Douglas 1982; Ostermann-Kelm et al. 2008). A manipulative field experiment involving
tethered domestic horses confirmed indirect interspecific competition as the mechanism
(Ostermann-Kelm et al. 2008). Eastern grey and red kangaroos also dissociate from cattle in
paddocks ranging in size from 0.1–3680 ha in semi-arid and arid environments, and a
behavioural mechanism could not be ruled out (Low and Low 1975; Southwell and Jarman
1987; Payne and Jarman 1999). There is sufficient overlap in the activity cycles of horses and
eastern grey kangaroos for initial behavioural antagonism to have occurred to establish a
precedent. Kangaroos are primarily nocturnal grazers, but eastern grey kangaroos are one of
the most diurnally active species of macropod along with the red-necked wallaby (Macropus
rufogriseus) (Kaufmann 1974, 1975; Clarke et al. 1995). Feral horses are diurnal and
crepuscular and can spend up to 70% of a 24-hour period grazing (Duncan 1985); both
species rest in the middle of the day in similar habitat types (Caughley 1964; Taylor 1980;
McCort 1984).
This is the first study to provide empirical evidence of macropods altering their
spatial distribution and potentially their foraging behaviour in relation to manipulated
numbers of feral horses. On the basis of this study and the literature, exploitative
competition and indirect interference competition were both plausible causal mechanisms.
Chapter 3. Indirect Effects on Macropods 84
A well-designed manipulative experiment would be required to understand the mechanism
underlying the dissociation between horses and macropods on Paddys Plateau and in the
gorge catchments.
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