Migratory Birds: Ecology and Conservation. A report on the
BOU’s Annual Conference held at the University of Leicester
5-7 April 2011.
Jenny C. Dunn
RSPB, The Lodge, Potton Road, Sandy, Bedfordshire. SG19 2DL.
In April 2011, the British Ornithologist’s Union’s annual conference
took place at the University of Leicester. The theme of this year’s
conference was the ecology and conservation of migratory birds,
and talks ranged from those focussed on either breeding, migration
or wintering ecology, to those linking two or more of these and
trying to build a more complete picture of the complex problems
faced by long distance migrants. Talks also covered recent
technological advances, which are increasingly allowing us
intriguing new insights, particularly into the seasonal movements
and wintering areas of some of the most declining species. Finally,
talks examined the policy challenges associated with protecting
migratory species and how best to tackle flyway-scale conservation
of migratory birds.
The talks highlighted the progress made in expanding our
knowledge of migratory routes and related staging and wintering
areas, thanks initially to the contribution of recovery information
from ringing studies, and more recently to advances in technology
such as geolocators and satellite tags (Baillie et al. 2009). These
techniques offer the ability to track individual birds throughout the
entire annual cycle, linking ecology on both breeding and wintering
grounds (Robinson et al. 2010) and providing crucial information
for the design of effective conservation strategies (Martin et al.
2007). However, as always, the amount that is still unknown was
also emphasised: much of this knowledge will be critical in aiding
our understanding of species’ ecology and thus increasing our
ability to effectively conserve migratory birds (e.g. Faaborg et al.
2010a).
The conference began with a welcome address by the BOU
President Dr Alistair Dawson and was followed by a keynote speech
by Professor Ian Newton OBE FRS FRSE entitled “The ecology of
bird migration patterns”. Professor Newton’s talk gave an
introduction to the history of research and knowledge of migratory
birds, as well as serving to highlight the differences between
obligate and facultative migrants. Obligate, or fixed, migrants
follow a fixed migration route, with individuals often returning to
the same breeding and wintering grounds year after year, a trait
thought to be largely under genetic control (Newton 2008). In
contrast, facultative, or irruptive migrants tend to migrate when a
declining food supply demands it, and show huge variation in both
timing of migration and migration route, differing even in the
direction of migration from year to year (Newton 2006).
Facultative migrants also show very little breeding or winter site
fidelity, as revealed by ring recoveries and stable isotope analyses
(Marquiss et al. 2008). Finally, Professor Newton suggested that
obligate and facultative migrants should be regarded more as a
continuum, rather than two distinct entities, citing the case of the
White Stork Ciconia ciconia which appears to have both an obligate
and a facultative section to its migration strategy (Berthold et al.
2004), continuing to wintering grounds further south if necessary
in order to take advantage of food availability.
The first three sessions of the conference focussed on migration
ecology, and the first of these opened with a keynote presentation
from Dr Peter Marra (Smithsonian Migratory Bird Center,
Washington) examining the implications of carry-over effects
between seasons, and between breeding and wintering grounds
(e.g. Inger et al. 2010). This talk emphasised the importance of
taking into account the entire annual cycle of migratory birds when
considering any aspect of their ecology, as seasonal interactions
may be common (Norris & Marra 2007, Reudink et al. 2009) and in
general, research has tended to focus on the breeding season
rather than at other stages of the annual cycle (Faaborg et al.
2010b). Satellite tracking technology has greatly increased our
ability to track the movements of individuals in some detail for long
periods, and the next talk by Dr Kaspar Thorup (Natural History
Museum of Denmark, University of Copenhagen, Denmark)
summarised data from a satellite tracking study, examining the
influence of perpendicular wind on the migration of first year
raptors as distinct from adults (Thorup et al. 2003). The raptor
theme was continued by Matias Juhant (University of Maribor,
Slovenia), who discussed the scarcity of knowledge regarding
raptor migration within South America, and emphasised the
importance of establishing monitoring programmes using migration
counts (Juhant 2010).
Dr Ulf Ottosson (A. P. Leventis Ornithological Research Institute &
University of Lund, Sweden) opened the second session, describing
a study of Garden Warblers Sylvia borin, trying to piece together
the story of this species’ migration through a series of ringing-
recapture sites in Africa and providing substantial insight into the
over-winter ecology of this species (Ottosson et al. 2005b). The
timing of migration has long been known to be under the control of
both exogenous and endogenous factors (Styrsky et al. 2004), but
how these interact to influence migration timing is less well known.
This was the focus of the next talk from Miren Andueza (University
of Valencia & Aranzadi Science Society, Spain) who described a
study of exogenous and endogenous factors in Sedge Warbler
Acrocephalus schoenobaenus migration, emphasising the
importance of considering all factors together, rather than each
separately, as additive effects may be common. The next talk from
Dr Volker Salewski (University of Osnabrück, Germany) discussed
the difficulties of differentiating between Eastern Iduna pallida and
Western Olivaceous warblers I. opaca (Ottosson et al. 2005a), and
of distinguishing resident from migrant populations of both species,
highlighting some of the complexities associated with
understanding the migration ecology of these two species. The use
of stable isotopes has increased dramatically over the past decade,
especially in North America (Bowen et al. 2005); however, their use
in Afro-Palaearctic migrants is less well developed. Dr Paul Donald
(RSPB, UK) spoke about stable isotope work trying to identify the
winter distribution of the Aquatic Warbler Acrocephalus paludicola
by comparison of stable isotope feather signatures with those of
resident African species within the same trophic guild (Flade et al.
in press). This talk also highlighted some of the difficulties with
this technology, such as the requirement for a detailed knowledge
of moulting ecology, pointing out that moulting areas and wintering
grounds are not necessarily the same. Consequently, these data
need to be accompanied by other complementary approaches,
followed by fieldwork to confirm likely wintering locations
(Buchanan et al. in press). Dr Elizabeth Yohannes (Max Planck
Institute for Ornithology, Germany) continued the stable isotope
theme with her talk providing an overview of the use of stable
isotopes in avian migration work, and citing an example of hybrid
Great Acrocephalus arundinaceus and Clamorous A. stentoreus
Reed Warblers with features of both species, where stable isotope
analysis enabled the location of hybrid wintering grounds to be
established (Yohannes et al. 2011).
The final migration ecology session began with a talk from Dr Rob
Robinson (BTO, UK) looking at large scale patterns of demographic
responses to climate change in Palaearctic warblers. For example,
decreased productivity in woodland species, where temperature
change was most rapid, suggested mismatches with the seasonal
peak in food availability. Similarly, increased productivity of reed-
dwelling species, where temperature change was greatest,
suggested that this habitat may be thermally limiting and
consequently that survival is responsible for population changes in
these species. The second talk in this session was from Dr
Fernando Spina (Istituto Nazionale per la Fauna Selvatica, Italy),
looking at fat reserves in Barn Swallows in relation to the timing of
roosting and migration. Dr Spina illustrated a relationship between
fat reserves and the size of habitat barriers, for example, deserts or
seas, along migratory routes, revealing that both adult and juvenile
birds with larger barriers to cross had larger fat reserves (Rubolini
et al. 2002). Teresa Militão (University of Barcelona, Spain)
followed this by discussing whether stable isotope analysis can be
used to trace migratory routes of Atlantic seabirds and concluded
that this method can detect species-specific migratory strategies,
but that knowledge of individual species’ moult strategies was
crucial in interpreting these data (Ramos et al. 2009). Dr Rob
Sheldon (RSPB, UK) closed this session by describing work using
satellite tags to establish the migration routes of the Sociable
Lapwing Vanellus gregarious, a species for which hunting on
migration has been identified as the key threat to the population.
Data from satellite tracking has enabled survey and monitoring
work to be targeted at key sites along the migratory routes used by
this species and hence provide crucial information that will aid the
development of appropriate conservation actions.
Dr Jenny Gill (University of East Anglia, UK) opened the next
session of talks, aimed at discussing responses to environmental
change, with a keynote presentation looking at the population-level
responses of migratory birds to environmental change, focussing
on the Black-tailed Godwit Limosa limosa. This long-term study
investigates the drivers of “seasonal matching” in this species,
where breeding and non-breeding ground habitat show marked
variation in terms of breeding success and over-winter survival,
and a very strong relationship exists between winter and summer
habitat quality within individuals (Gunnarsson et al. 2005). Strong
seasonal matching is seen only in males, not females and
consequently it is thought to be driven by natal site fidelity and
may have profound implications in terms of inflating fitness
inequalities driven by habitat quality (Gunnarsson et al. 2005).
Next, Professor Brian Huntley (University of Durham, UK)
described work utilising 20 years of survey data to create models
predicting distributional responses to climate change in migrant
species. These models predicted shifts in both breeding and non-
breeding ranges resulting in a predicted 25% increase in migratory
distance (Doswald et al. 2009), although a change in migratory
strategy was proposed as an alternative possibility, whereby sub-
Saharan migrants could potentially winter north of the Sahara as
habitat becomes suitable. Alternatively, birds may respond to an
increased availability of habitat suitable for breeding and wintering
and consequently become resident in part of their range. Adam
Seward (University of Cardiff, UK) followed this by presenting
results from supplementary feeding experiments in breeding
Northern Wheatears Oenanthe oenanthe, where pairs provided
with supplementary food were more likely to have an extra
breeding attempt, and recruit offspring into the breeding
population.
The second day opened with a second session discussing responses
to environmental change and began with a talk by Dr Silke Bauer
(Swiss Ornithological Institute, Switzerland) looking at how
environmental change might affect the departure cues used by
birds in timing their migration. This talk emphasised how little we
know about the external cues affecting departure dates of migrants
and the need to develop a greater understanding of these cues
before we can predict the consequences of environmental change
for migrant species. Catriona Morrison (University of East Anglia,
UK) continued this session by discussing contrasting population
trends between Willow Warblers Phylloscopus trochilus in Scotland
and the south east of England (Morrison et al. 2010), with nest-
specific rainfall data showing high failure rates in warm and dry
conditions. Urbanisation causes changes in microclimate that may
impact upon bird behaviour through higher temperatures and
greater food availability (Partecke & Gwinner 2007), and Mikkel
Kristensen (Copenhagen Natural History Museum, Denmark)
discussed the possibility of distinct migration behaviour between
urban and rural birds. Urban populations did appear to have
adapted to these changes, with both blackbirds and great tits
reducing their migration distance compared to their rural
counterparts, and urban blackbirds showing a decrease in the
number of migrating individuals, suggesting a higher degree of
residency. Next, Dr Juliet Vickery (RSPB, UK) discussed early
results of a large-scale project in Ghana and Burkina Faso
monitoring migrants across a range of habitat types and
highlighted the importance of using multiple conservation tools,
considering socio-economic impact of conservation actions, and
taking a co-ordinated flyway approach when dealing with migratory
species. This session was concluded by a Techspot from Vicky
Jones (Birdlife International) introducing the Critical Site Network
Tool, a tool for conservation planning and management of
waterbirds accessible at www.wingsoverwetlands.org/csntool.
The next session focussed on the practicalities of putting science
into practice in terms of management for migratory birds, and
began with a talk from Dr José Alves (University of East Anglia, UK)
looking at the energetic costs of geographic variation in Black-
Tailed Godwit wintering grounds, and showing that the costs of
migrating longer distances and over-wintering further south are
outweighed by lower energetic living costs and reflected in an
earlier arrival date on breeding grounds and an increased
reproductive success. Dr Nigel Clark (Delaware Shorebird Project
& BTO, UK) followed this by describing the difficulties involved in
establishing compromise between interested parties where
overfishing of Horseshoe Crabs Limulus polyphemus at the final
stopover site for Red Knot Calidris canutus in Delaware Bay has led
to a catastrophic decline of this species (Haramis et al. 2007).
Whilst no long-term management solution has yet been established,
a major hurdle has been overcome as fishery groups now
appreciate that management of Horseshoe Crab fishing is essential
for the recovery of Red Knot populations. Conference talks then
moved on to the implementation of conservation through policy,
focussing first on the construction of Species Action Plans (SAPs),
with Tim Jones (DJEnvironmental, UK) discussing the problems
faced when constructing and implementing action plans for
migratory species, emphasising the need for international
supported and cooperation and a mutual shared will over a large
geographic scale. Dr Norbert Schäffer (RSPB, UK) described one
example of a successfully implemented action plan, the EU SAP for
the Corncrake Crex crex, which was largely driven by changing
mowing practices in the breeding areas to enhance nestling
survival (Schäffer & Weisser 1996). Many lessons learned from the
Corncrake SAP have been incorporated during the development of
the SAP for the Aquatic Warbler: SAPs are more likely to be
successful when a species faces similar problems across its whole
range, and when the SAP is ‘owned’ by an individual or institution,
and driven by the chairman of the working group. Dr Tim Stowe
(RSPB, UK) concluded this session by examining practical
approaches to implementing conservation strategies for African-
Eurasian migrants, emphasising that whilst an international
agreement is a very important start it needs to be complemented
by action on the ground at regional and national levels. The
identification of key wintering and stopover sites are particularly
important for waders and soaring birds; however, there are still
many unanswered questions regarding the migration of passerines
which migrate on a broad front, and conservation resources need
to be focussed on identifying key habitats and locations in the sub-
Saharan region in order to gain a greater understanding of factors
influencing population declines of these species.
Professor Franz Bairlein (Institute of Avian Research, Germany)
opened the final session, discussing future knowledge and policy
needs, with a key-note presentation discussing current knowledge
and future perspectives for the effective conservation of migratory
birds. Professor Bairlein’s talk emphasised the importance of
stopover sites and concluded by stressing the importance of
integrating theory with reality and identifying the mechanisms
driving population trends for each species. Declining population
trends are generally associated with a lack of adaptation to
changing conditions; however, Professor Hanna Kokko (Australian
National University, Australia) pointed out that interpretation of
population trends resulting from environmental change can be
tricky, citing a model of partial migration in Finnish Skylarks
Alauda arvensis where a higher proportion of the population
remaining resident as a result of climate change could potentially
lead to population declines as a result of increased adaptation. The
final talk of the conference was from Dr Ian Bainbridge (Scottish
Natural Heritage, UK), examining future projections for the
requirements of migratory birds. Future conservation strategies
need to take into account both daily and annual cycles; however,
policy tends to be less effective across annual cycles and site-based
conservation measures work better for some species than others,
highlighting the need for flexibility. Site-based conservation is
particularly difficult when species are mobile over-winter and
frequently a lack of knowledge as to the location of wintering
grounds hampers conservation efforts. Human population growth,
with it’s associated habitat destruction and degradation is likely to
be one of the biggest problems restricting conservation effort for
migratory birds.
Dr Danaë Sheehan rounded off the conference with a summary,
reviewing the approaches, challenges, and priorities for future
research highlighted throughout the conference. Many challenges
were suggested: one of the main priorities should be seen as
getting these issues onto the agendas of multilateral agreements
and making them effective. Research priorities tended to focus on
factors on wintering grounds – such as identifying key drivers of
population trends, investigating socioeconomic drivers, habitat
choice, and factors driving variation in seasonal survival and
regional variation in population trends. Investigating factors
driving declines in migratory seabirds, managing water and
wetlands for migrants in a changing climate, and establishing the
effects of climate change on productivity and migration strategies
were also among those issues highlighted as research and
conservation priorities.
The BOU awarded prizes for the best student poster and talk at the
conference. The prize for best student poster went to Helen
Anderson for her poster entitled “The benefit of early arctic
snowmelt for Pink-Footed Geese”, and best student talk to Teresa
Militão for her talk on stable isotope analysis and the migration of
Atlantic seabirds.
A conference like this could not take place without an efficient
organising committee, and thanks go to Dr Helen Baker (JNCC), Dr
Danaë Sheehan (RSPB), Dr Jacquie Clark (BTO), Dr Karl Evans
(University of Sheffield), Dr Peter Jones (Edinburgh University), Dr
Phil Atkinson (BTO), Steve Dudley (BOU) and Angela Langford
(BOU) for the smooth running of an extremely successful
conference.
Acknowledgements
References
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