brussels - aves.be · brussels is situated in the brabant natural area of silt-sand soils, a region...

ANNE WEISERBS & JEAN-PAUL JACOB

BRUSSELS

INTRODUCTION AND FEATURES

Historical development of the city

Brussels is an old city, founded in 977 A.D. on islands in the valley of the Senneriver, a minor tributary of the Escaut river. The history of the city is intimately linkedwith the development of crafts and industry (particularly the production of cloth)along the Senne and its tributaries (including the Woluwe, Geleytsbeek, Pede andMolenbeek). The expansion of the city accelerated from the 19th century, steadilyabsorbing the surrounding villages into the urban fabric. Like most other cities,Brussels has undergone massive urbanisation, quite unplanned and unaesthetic, espe-cially during the second half of the 20th century. This has been exacerbated by thecity’s increasing role as an international hub, in particular as the seat of the EuropeanCommission and of many other organisations. One result has been the decline andtransformation of natural habitats. Drastic modifications of the Brussels landscapehave sometimes taken place over very short periods of time. An example is provid-ed by the marshes and wetlands that formerly occupied the valleys of the BrusselsRegion. In 1770 they covered 224 ha, by 1979 this had been reduced to only 59 haand by 2003 they have virtually disappeared, having been transformed into artificialponds or completely dried out (Onclincx & Desager 1997).

Present character and features of the city

The political and administrative region of Brussels extends over 162.38 km² and hasa population of about one million people. However, the outskirts extend widely overthe country’s two other political regions (Flanders and the Walloon region), and forma continuous unit that extends to the nearest towns (Louvain, Malines and Wavre).This chapter is limited strictly to the region known as Bruxelles-Capitale.

Brussels is situated in the Brabant natural area of silt-sand soils, a region of moreor less wooded hills drained by some large river valleys (for example the Senne andthe Dyle). Its altitude is between 15 and 130 metres above sea level (asl). The climateis of the Temperate-Atlantic type, that is cool summers and damp, mild winters.Brussels is the principal city of Belgium (c. 10 % of the Belgian population), con-siderably larger than Anvers (population c 700,000) and several towns of lesserimportance (Gand, Liège and Charleroi with human populations of 200,000 to250,000).

The region is characterised by its small proportion of undeveloped land (36 %,compared with an average of 84 % for Belgium). In addition, land use for economic

John G. Kelcey & Goetz Rheinwald (eds.): Birds in European Cities, 81-101©2005, GINSTER-Verlag, St. Katharinen

and social purposes is mainly devoted to the service sector: shops, offices, ware-houses and educational institutions. A significant proportion of the land (21 %) istaken up by the highly developed road network and railway lines. The Senne riverhas been culverted, as a result the only open-air waterway crossing the city is the nav-igable canal that links Anvers and Charleroi and which makes Brussels the fourthlargest inland port in Belgium.

The architectural history of the city has produced a mosaic of different districts.The oldest ones, especially those of the city centre, are typified by a high density ofbuildings and a maximum coverage of the land by hard surfaces. Some other districtshave been modernised; the landscape being shaped by buildings of various heights,some of which are impressive. The surrounding suburbs are made up of mainly res-idential districts together with the expanding businesses and services in associationwith the communication network.

In the region of Brussels, the indigenous fauna is completely protected by the rul-ing of 27 April 1995 relating to the safeguarding and protection of nature in Brussels.In addition it benefits from the present willingness of the regional authorities to cre-ate an ecological network, which will, in theory, ensure that the green spaces aremanaged in a way that favours biodiversity. This willingness includes the proposal toretain three areas totalling 1871 ha, of which Soignes Forest constitutes the mainpart, within the Natura 2000 network of sites of EC (European Commission) impor-tance. It is therefore to be hoped that there will be a reversal (or at least the slowingdown) of the loss of natural habitats.

Present city ecosystems/habitats (Figures 1a and 1b)

New or restored buildings often provide few opportunities for the urban avifauna incomparison with the older districts. Older buildings, unlike modern structures, havebalconies and are well-provided with crevices, which offer more opportunities, espe-cially for hole-nesting species. The rapid redevelopment of entire districts is aprocess that has been particularly noticeable in Brussels, to the point that it has givenrise to the expression “Brusselisation”.

A bit more than half of the Brussels area (8,500 ha) is composed of green spaces.Private gardens account for around 3,600 ha, that is 22 % of the region’s territory.The structure of the gardens is related to a large extent to the degree of urbanisation.Enclosed islands of greenery can be found in the very centre of the city, created bythe gardens of adjoining houses. Patches of lawn a few metres square separated byhigh walls are the most common feature. At the other extreme, the more residentialareas provide a continuum of large gardens, often with trees.

In addition, public parks often include wooded areas of variable size. Createdmostly in the 19th and early 20th centuries, they also constitute a significant area(1,040 ha) to which may be added the 160 ha of the Royal Park. Many of these areprotected, that is, any development proposal is subject to ministerial authorisation.Further habitats are provided by the embankments along the railway system (220 ha),as well as several cemeteries (147 ha), which are often well-vegetated. The green

82 A. WEISERBS & J.-P. JACOB

spaces associated with the transport network (235 ha) do not provide much addition-al habitat; however there are some notable rows of trees.

Waste land (515 ha) and agricultural areas (515 ha) are subject to constant pres-sure in terms of urbanisation and are partly categorised as land reserved for furtherdevelopment. They contain vestiges of the rural landscape: hedges, lines of pollard-ed willows (Salix spec.) and orchards.

Around the periphery, two forested areas recall the former existence of the vastforests of Brabant: the Laerbeek wood (35 ha) to the north of Brussels and the SoignesForest in the south (4,383 ha, of which 1,654 are included in the Brussels Region).

Few wetlands have retained their natural character: only a few protected areasinclude habitats of notable quality for an urban environment (the marshes of Jette andthe Hof ter Musschen for example). On the other hand, the many ponds includedwithin the public parks generally have an artificial character, with man-made banks.Some of the woodland ponds and pools have a more natural aspect, in contrast toponds in private gardens, which are often highly artificial and much smaller.

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Figure 1a. Map showing green spaces, wetlands and main transport routes in Brussels

There are hardly any other semi-natural habitats in Brussels (former heath landfor example).

Present vertical and horizontal structure of urban habitats

Generally speaking, the degree of urbanisation increases towards the centre (Figure1b). In the historical centre green spaces are rare and gardens limited. Moving awayfrom the centre, the influence of buildings progressively decreases and the buildingstake on a more residential character. This zone is characterised by numerous parksand the gardens, which when aggregated form green islands surrounded by blocks ofhouses. Elsewhere in the zone, residential areas are characterised by groups of exten-sive properties, notably close to the Soignes Forest. The proportion of green spacesis therefore unequal: around 10 % in the centre of the town, 30 % in the inner sub-urbs and 71 % in the outermost suburbs.

NATURAL HISTORY OF THE BIRDS OF BRUSSELS

Historical aspects of the avifauna before 1940 and between 1940 and 1990; changesin the ecosystem

The composition of the urban avifauna is influenced to a large extent by the abun-dance and quality of the habitats present in and immediately surrounding the city.


Figure 1b. Degrees of urba-nisation in the Brusselsregion. Medium grey: hea-vily built-up; light grey:rural influence; white: resi-dential influence; dark:woodland influence andpublic open spaces.

Nevertheless, the political region (Brussels-Capital) does not include part of thecity’s outskirts.

Formerly of course, the territory of the present city included a larger proportionof natural habitats and countryside. It is for this reason that, for example, up to 1850AD Red-backed Shrikes were still nesting in the Maelbeek valley, where the head-quarters of the EC and the European Parliament now stand. During the second halfof the 20th century, urbanisation in the Brussels region has brought about a particu-larly marked decline in the countryside and in many semi-natural habitats. This rapidurbanisation has resulted in impoverishment of the avifauna, partly mitigated by thearrival of new species. Thus, over very variable time scales (sometimes in just a fewyears) a number of species have decreased or become extinct while others have adapt-ed and even increased.

It should be borne in mind that ornithology has itself evolved considerably dur-ing the second half of the 20th century, especially since the 1960’s. Information hasbecome more and more centralised, especially thanks to the birth of Non-Govern-mental Organisations such as AVES. More recently, professional cooperation andcoordination has allowed large surveys to be undertaken, resulting in the first BelgianBreeding Birds Atlas (Devillers et al. 1988) between 1973 and 1978, and the firstAtlas of Breeding Birds of Brussels (Rabosée 1995) over the period 1989-1991.

The presence of a number of species before 1940 is uncertain. Since then, at leastone regular nesting bird has disappeared, the Ortolan Bunting, as well as three occa-sional nesters: Little Bittern, Woodlark and Pied Flycatcher. There is limited data tosuggest the possible former presence of four additional species: Grey-headed Wood-pecker, Northern Wheatear, Lesser Grey Shrike and Woodchat Shrike (Rabosée1995). All these species are currently absent from the Brabant province, which his-torically included Brussels.

Between 1940 and 1990, at least 13 indigenous species appeared, at least as occa-sional nesters: Great Crested Grebe, Grey Heron, Pochard, Tufted Duck, HoneyBuzzard, Kestrel, Hobby, Lapwing, Woodcock, Collared Dove, Fieldfare, Crested Titand Reed Bunting. Their arrival results mostly from increases in the Belgian popula-tions and/or their national or continental breeding ranges. Some of them are current-ly threatened because of habitat losses and a decline on the national scale (Lapwingand Reed Bunting for example).

During the same period, not less than nine regular breeders have disappeared:Hoopoe, Crested Lark, Sand Martin, Whinchat, Savi’s Warbler, Sedge Warbler, GreatReed Warbler, Rook and Corn Bunting. Some of them could reappear, at least tem-porarily, either because they continue to breed close to Brussels, or because there arestill suitable habitats available (for example for farmland birds). Goshawks are stillpresent in the Soignes Forest, but only occur irregularly in the Brussels section.

Eight occasional nesters have ceased to breed since 1940: Quail, Water Rail,Wryneck, Nightjar, Bluethroat, Red-backed Shrike, Great Grey Shrike and CirlBunting. In addition, Cetti’s Warbler furtively appeared in the 1970’s.

Table 1 summarises the changes in the avifauna in the various types of habitatduring the period 1940-1989. The greatest losses have occurred among birds of open

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countryside, semi-open and edge habitats, and to a lesser extent those associated withwetlands. New species are mainly waterfowl and tree-dwelling species. The resultsshow, not unsurprisingly, that the disappearance of a species is caused by a quantita-tive and/or qualitative decline in the quality of its habitat. The appearance of newspecies may be attributed to supra-regional changes. Further, the typically urban avi-fauna (generalist species and those nesting on buildings) has changed very little overthis period.

Table 2 shows a summary of the changes in numbers of species during the pastcentury. Overall, a total of 122 species have nested at least once in Brussels. If vari-ous periods of the century are examined, the total number of nesting species is fair-ly stable. However, this masks a fairly large turnover rate (28 %); a maximum of 80species have nested regularly at the scale of the whole century (there is still someuncertainty regarding 27 of them). The second half of the century shows a decline ofthe indigenous avifauna compensated by the establishment of alien species.

Characteristic features of the avifauna in the 1990’s and 2000’s

The breeding avifauna of the last 15 years is well-known, thanks to a multitude ofobservations, the carrying out of two successive breeding bird atlases (1989-1991and 2000-2004: Rabosée 1995; Weiserbs & Jacob, in prep.), and the monitoring sys-tem for urban nesting birds (Jacob 1992; de Schutter et al. 1998).

This avifauna comprises a total of about 100 species (listed in the appendix),which is to be expected for an urbanised area of the size of Brussels. The currentindigenous avifauna is composed of at least 92 species; the nesting of three further


New species Disappearance of species

Regular Occasionalbreeders breeders

Water/marsh 5 3 2Open country 2 6 3Generalists 1 - -Wooded areas 4 - 3Urban habitats 1 - -

Table 1. Evolution of the avifauna during the period 1940 - 1989.

Table 2. Evolution of the avifauna during the last century.

> 1940 1940-1960 1961-1968 1973-1977 1989-1991 1991<

Indigenous breeders 78-108 91-104 93-99 91-97 89-94 92-95Introduced breeders 2-3 2-3 2-3 5 7 11Total 80-111 93-107 95-102 96-102 96-101 103-106

species is unconfirmed. By comparison, some semi-wooded and diverse open-coun-try habitats scarcely have more species (103 in 279 km² of the Belgian Famenne,Jacob & Paquay 1992), while some more intensively farmed areas have fewerspecies (70-80). An important characteristic of the Brussels avifauna is the large pro-portion (10 %) of alien species. This aspect is discussed later in this chapter.

The avifauna exhibits wide variations in terms of population density. Figure 2shows the abundance distribution of indigenous species. Out of a maximum of 94species, at least 40 % have a population of fewer than 20 pairs. These are mostlyspecies associated with open or semi-open habitats such as the Little Owl,Goldfinch and Nightingale; woodland species (especially raptors) and to a lesserextent wetland species, such as Kingfisher and Grey Wagtail. Further, in terms oftotal numbers, some fifteen species make up 80 % of the Brussels avifauna, the mostabundant being, unsurprisingly, generalist and/or anthropic species. These speciesare favoured by the goodwill of the public and by the general absence of human per-secution and because all the indigenous avifauna in the Brussels Region are pro-tected. Some species are particularly well adapted to cities: the Woodpigeon, whichbreeds in over 99 % of the territory, is a striking example. Other species are able tobreed in small and degraded green spaces; they are also distributed throughout theterritory, including the city centre: they notably include small passerines such asRobin, Dunnock, Wren and Starling, but also corvids such as Magpie and CarrionCrow.

The distribution of species is strongly influenced by the degree of urbanisation:hence the number of species increases along a centrifugal gradient (Fig. 3). Over the

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Figure 2. Abundance distribution of indigenous species.

period 1989-1991, an average of 36 species per km² was recorded, the lowest densi-ty being 12 species/km² in the most intensely urbanised habitats and the highest 71species per km² in areas with a wide diversity of habitats (Rabosée 1995).

Among the anthropic species, Swift and House Sparrow are present in large num-bers, although it is difficult to estimate their numbers accurately. The Black Redstartis widely distributed, though less abundant (100 to 500 nesting pairs).

The opportunities presented by gardens depend on their structure and size. Thesmall green islands included within blocks of houses in the city centre offer nestingsites only to generalists and to the less demanding small passerines, such as Greatand Blue Tits. On the other hand, the extensive properties around the periphery sup-port a complex avifauna, enriched by woodland species such as Nuthatch, Marsh Tit,Goldcrest, Hawfinch and Bullfinch, as well as species of edges and semi-open habi-tats such as Green Woodpecker and Spotted Flycatcher.

The parks generally comprise open lawns with wooded areas of variable size thatsupport generalist species and woodland birds with small territories. Some parks(parc Duden and parc du Cinqantenaire) provide better-quality habitats and supporta diversity comparable with the large properties. Their species richness varies aroundthirty nesting species.

The wetlands are of varying interest depending on their management and degreeof restoration. Proposals by the city's admininstration to create more natural habitatssuch as reedbeds favours passerines of wetland habitats, such as Reed Warblers. Inthis context, several nature reserves and some properties which are closed to the pub-lic as the Val Duchesse Castle and the Royal Park make an imporant contribution tothe avifauna of Brussels and support some species which are more sensitive to habi-tat quality, such as Little Grebe. The populations of these more sensitive speciesremain very low. The construction and management of the majority of the ponds inthe city centre parks are not attractive to water birds, for example, the presence of


Figure 3. Number of spe-cies present in relation tothe centrifugal urbanisa-tion gradient. Centre:historic city centre; suburb1: sub-region under urbaninfluence; suburb 2: sub-region under woodlandinfluence; woodland:Soignes Forest (see alsoFig. 1b).

artificial banks and/or frequently mown lawns up to the edge of the water and theabsence of aquatic vegetation. The avifauna of these ponds is reduced to a few unde-manding species such as Mallard, Moorhen, various domesticated ducks and geesethat have been released (or escaped) and aliens. This farmyard-type avifauna is wellfed by the public. The large amount of leftover foodstuffs thrown into the water(mainly bread) constitutes an input of organic pollutants that contribute to the dete-rioration of the quality of the aquatic habitat.

The forest areas have changed little during the last few decades. Their avifaunais richer overall than that of the city because of the diversity in the structure andspecies composition of the plant communities (avifauna of conifer plantations andwoodland clearings, for example) and to their extent, which allows birds with largebreeding territories to establish, such as Black Woodpecker, Buzzard, Honey Buz-zard, Tawny Owl and Long-eared Owl. However, as will be described later, severaltypical woodland species are undergoing marked decline.

The railway embankments, cemeteries and waste lands,which in total occupyonly a small area of the city, have become practically the only areas in which speciesof semi-open habitats occur, for example Lesser Whitethroat, Goldfinch and IcterineWarbler. Artificial open areas (operational and old industrial zones) are occasionallyused for nesting by Little Ringed Plovers.

The continual decrease of farmland over the last 50 years explains the disappear-ance of species and the risk of extinction for the remaining ones: Yellow Wagtail,Yellowhammer, Skylark, Linnet or Partridge.

Gains and losses in species

During the last fifteen years, many species have undergone rapid changes, often con-tinuing the trends described previously.

Several species that are declining in Belgium have decreased more in Brusselsduring the 1990’s than in neighbouring regions. This is true especially for speciesthat were once common in the wooded areas and at their edges: Turtle Dove, TreePipit, Golden Oriole, Cuckoo, Redstart and Wood Warbler. During the 1990’s, thesize of their populations has substantially declined to such an extent that they are nowconsidered to be virtually extinct in Brussels, even though occasional nesting stilloccurs. Similar situations are reported from other urban areas in Belgium and else-where in Europe in respect of other species, for example House Sparrow, HouseMartin and Swallow. Only the House Martin, which underwent a 90 % decrease over20 years, now seems to be stabilising at or about 50-60 nesting pairs since 1997(Weiserbs & Jacob 1996, 2001).

Other species have (re)appeared, there are two remarkable examples. First, thePeregrine, which bred in 2004 for the first time for almost 70 years. Second, theMiddle-spotted Woodpecker, a specialised woodpecker, was restricted to woodedregions in the south of Belgium until about 1995. However, it has subsequentlyspread rapidly and was confirmed as a breeding species in the Soignes Forest in 2002(Samyn pers. com.).

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Changes in the most widely distributed species have been monitored since 1992thanks to a programme of point-counts that has been incorporated into Brussels envi-ronment survey excercise. The Point-counting Programme is carried out twice peryear at one hundred sampling points – observers standing at the sampling point andcount the number and species of birds heard or seen during fifteen minutes. FewEuropean cities benefit from similar monitoring. From the first decade (1992-2001)of point counts there were sufficient data for the statistical analysis of change in thestatus of 33 species (Weiserbs et al. 2002). Of the 33 species, eleven showed signif-icant changes. Five species generally associated with wooded and open habitats aredeclining, namely Marsh Warbler, Greenfinch, Willow Tit, Willow Warbler andDunnock. Five species associated with wooded habitats showed an increase: Short-toed Treecreeper, Blue Tit, Jackdaw, Green Woodpecker and Goldcrest and there wasa marked increase of one alien species, Rose-ringed Parakeet.

Although an increase in the numbers of some generalist corvids, such as CarrionCrow and Magpie, is frequently suspected, especially by the public, the monitoringsurvey does not show any recent significant increases.

Movements/ fly over/ migration

Brussels is situated in a region of low hills and wide valleys. Some suitably orientedvalleys, in particular those of the Senne and the Woluwe, contribute to the chan-nelling of the migratory movements, which take place on a broad front acrossBrabant. Migrations have been monitored at several stations for many years, forexample at Boitsfort, on the line of the Woluwe stream, where over a hundred specieshave been noted on passage. The city centre, highly built-up and dotted with build-ings of moderate size (not more than 150 m high) provides fewer sightings, possiblybecause birds avoid the area or fly over at a higher altitude. Nevertheless it does notpreclude the passage of many species over the city, sometimes including unexpectedbirds, as shown by the kills of the Peregrine Falcons, wintering on the towers of theCathedral of Saint-Michel, next to the Grand Place of Brussels. The species takenincludes Little Grebe, Water Rail and Woodcock.

RoostsIn addition to the migratory flights there are daily movements of species gathering aturban roost sites, either throughout the year or seasonally.

In winter, roosts of Collared Dove, Greenfinch, White Wagtail, House Sparrowand thrushes may be seen in clumps of bushes, including those in the city centresquares. Buntings and other seed-eaters gather in damp places and scrubby areas onthe outskirts. On the fringes, gulls (Black-headed, Herring, Common and LesserBlack-backed) gather on open water and industrial buildings. Roosts of Cormorantsare confined locally to trees overhanging the water. Generally speaking, these influx-es are moderate, especially in the centre of the city, or are difficult to locate (forexample anthropic passerines such as the Greenfinch).

Some roosts may be seen throughout the year, like those of various corvids(Jackdaw, Carrion Crow, Rook, Magpie) and Starling. The birds gather on buildings


or in rows of trees, in parks, wooded areas and similar places. The size of the roostsis variable, reaching 400-500 birds in the case of the Magpie, 4.000-5.000 for theother corvids (as in the Royal Park) and gulls, and tens or even hundreds of thou-sands of individuals for the Starling. The roosts of small passerines are smaller anddo not often exceed one hundred individuals. As will be described later, several thou-sands of Ring-necked Parakeets gather in a single roost for the whole of the city andits outskirts, this roost also attracts a small population of Alexandrine Parakeet.

Some roosting movements lead the birds far away while some simply cross Brus-sels, for example the gulls that travel between the rubbish tips where they feed, 30km south of Brussels, and their roosts near Malines, 30-50 km north of the capital.

Wintering avifaunaThe wintering avifauna includes about 70 regular species. Most are also present inthe region during the breeding season. Several of them penetrate further into the cityin winter, for example the Grey Wagtail.

Among the other species, some birds which nest in Belgium only a short distancefrom Brussels may be found, they include Cormorant, Shoveler, Gadwall, Teal,Water Rail, Snipe and Black-headed Gull. Birds from more distant regions may alsobe found, such as Jack Snipe, Herring Gull, Common Gull, Lesser Black-backedGull, Redwing, Water Pipit, Siskin, Crossbill and Brambling. Some, such as HoodedCrows, have disappeared as their wintering area retreated towards the north.

The origin of the wintering bird population is often complex. Those regional birdsthat only travel short distances mingle with the long-distance Scandinavian immigrants(as is the case with the Robin for example). Their numbers remain limited to a few tensor hundreds of individuals (Pochard, Tufted Duck, Gadwall, Shoveler, Teal, Coot andMoorhen). In the specific case of waterbirds, no site of great importance is to be foundduring mild winters in Brussels (at the most a few hundred birds at the most suitablesites). During cold weather, concentrations build up on the canal and in the port area,which remain ice-free. Numbers can then reach several thousand individuals (mainlyPochards and Tufted Ducks). Despite the fairly mild winter climate (mean January tem-perature +3.5 °C), a few summer visitors attempt to overwinter; for example BlackRedstart, Blackcap, Firecrest and Chiffchaff occur only sporadically during the winter.Depending on the crop of beechmast is low or high, the influx of wintering species andmigrants (particularly Woodpigeons and Bramblings) can be spectacular.

MoultDuring the moulting period, several species, especially wildfowl, form local flocks.The concentrations are especially spectacular in the case of the Egyptian Geesewhich gather in large numbers every year in the Sobiesky Park in the north ofBrussels; over 350 individuals were counted in 2001 (Vangeluwe, pers. com.).

Alien SpeciesAn outstanding feature of the last 30 years has been the increase in alien birds inBrussels. The alien avifauna is composed partly of single individuals and/or of

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species which are not adapted to the local climate and whose presence is anecdotal.The appearance of alien birds is sometimes a result of the wishes of the persons incharge of the parks: this is the case with Peafowl. Escapes from captivity or deliber-ate releases by private individuals explain many of the observations: various parrots,notably parakeets of the genera Psittacula, Ara and Amazona, Budgerigar, Cockatiel,Sulphur-crested Cockatoo, and Senegal Parrot, waterbirds such as Barnacle Gooseand other species such as bulbuls, Tristram’s Grackle and Brahminy Kite. The fleet-ing presence of these isolated individuals is considered to have no impact on theindigenous avifauna.

Some species, mainly wildfowl and parrots, are able to acclimatise; these cur-rently account for 10 % of the Brussels avifauna (Table 4). It is possible, even prob-able, that new species will be added in the near future. The resulting colonisation ofhabitats could cause increasing competition between the populations of alien andindigenous species. Only those alien species that breed constitute a potential threatto the indigenous avifauna, these are discussed below. Alien passerines do not accli-matise in Brussels as they do in southern Europe. In general the abundance of thenon-indigenous populations is small, only the Ring-necked Parakeet and the FeralPigeon appear among the most abundant species in Brussels.

In addition, the presence of some free-flying domesticated waterfowl cannot beignored. Firstly, their presence in large numbers accentuates the highly artificial char-acter of the avifauna of some of the pools and could create problematic pressure onthese sites. Secondly, the frequency of Mallard hybrids poses a problem for thegenetics and conservation of this species.

It is noteworthy that the avifauna is not the only group of plant and animal species inBrussels that includes alien species. For example the Brussels flora includes about 50 nat-uralised alien species out of a total of 770 species (Saintenoy-Simon 1998), the mammalspecies include a population of the Siberian Chipmunk (Tamias sibiricus) and amongamphibians there is an increasing abundance of the Marsh Frog (Rana ridibunda).

ParrotsThree species of parakeets are breeding in the Brussels region, two of them havebeen doing so for about thirty years. Ring-necked Parakeet. The origin of the Brussels population is attributed to therelease of about 40 individuals as a result of the closure of an animal park in 1974;the first nests were seen in the same year. The whole of the population gathers everynight at a single roost. Although the location of the roost has changed several times,it has never divided. The roost is currently inside the NATO site, where it has beensince 2002. Censuses carried out at the roost have enabled the whole population tobe counted, which provides a reliable method for monitoring population changes(Fig. 4). The results indicate that the population has increased exponentially, withalmost 5,300 individuals counted in 2002 (Weiserbs & Jacob in prep.).

The population increase has been accompanied by the gradual colonisation of theBrussels territory and the current range extends widely across Brabant outside the


Brussels region. The highest densities have been recorded in the area first colonised:not less than 71 holes were occupied by Ring-necked Parakeets in 2000 in a smallwooded area covering 25 ha to the north of the city (Janssens pers. com.). It shouldbe stressed that in this area, suitable holes are particularly plentiful. On the otherhand the species is still uncommon in the Soignes Forest.

General monitoring of the avifauna of the Brussels Region indicates that thespecies is not having a negative effect on any indigenous species. Feeding resourcescould constitute a limiting factor; however the parakeets are well fed (with peanutsand fruit) by the city’s inhabitants. At first sight the availability of holes for nestingappears to be the most likely cause of competition with indigenous species. Howeverthe number of indigenous hole-nesters likely to suffer from this type of competitionhave not shown any negative trends, since at least 1992 in the case of Stock Dove,Green Woodpecker, Great Spotted Woodpecker, Jackdaw or Starling (Weiserbs et al.2002) (Fig. 5).

Monk Parakeet. This South American species constitutes a unique case among par-rots, in that it builds communal nests from twigs and sticks; the nests can sometimesmeasure several metres in diameter (Juniper & Parr 1998). The colonial nest is alsoused as roost. Throughout the day small groups of birds will leave the nest to feedand then return to it.

Monk Parakeets have been present in Brussels since the end of the 1970’s (deSchaetzen & Jacob 1985), the population being one of the most northerly in Europe.The colonial nests are monitored providing data that allows changes in the numbersof birds to be assessed. The population fluctuates, with distinct periods of expansionand decline. Currently, the population is expanding with more than 20 nests and morethan 150 individuals. In Brussels, the built up areas are especially colonised by thisspecies, as a result, the impact on the indigenous avifauna is low, given that the birds

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<1940 1940- 1961- 1973- 1989- >19911960 1968 1977 1991

Mute Swan - Cygnus olor + (?) + (?) + (?) + + +Black Swan - Cygnus atratus - - - - - +Canada Goose - Branta canadensis - - - - - +Egyptian Goose - Alopochen aegyptiacus - - - - + +Mandarin - Aix galericulata - - - - + +Magellan Goose - Chloephaga picta - - - - - +Pheasant - Phasianus colchicus + + + + + +Feral Pigeon - Columba livia + + + + + +Ring-necked Parakeet - Psittacula krameri - - - + + +Alexandrine Parakeet - Psittacula eupatria - - - - - +Monk Parakeet - Myiopsitta monachus - - - + + +

Table 4. Status of introduced species during the 20th century.

meet only few generalist species. Artificial feeding is probably essential for the sur-vival of the species (Weiserbs & Jacob 2000a).

Alexandrine Parakeet. The first observations of the Alexandrine Parakeet date from1998, very probably as the result of individuals escaping from captivity. Since it wasfirst recorded, the Alexandrine Parakeets has mingled freely with the Ring-neckedParakeet population in various aspects of their behaviour such as nesting, feeding androosting. In 1999, six nesting pairs were discovered (Scaillet 1999 and pers. obs.), withnine nesting pairs being counted in 2000. The population, which is one of the very fewfound in Europe, is currently estimated at 20-30 individuals (Weiserbs et al. 2001).

As with the Ring-necked Parakeet, the question arises of the impact on indige-nous hole-nesters. The Alexandrine Parakeet is more robust and therefore the inter-actions could be different, for example competition for larger holes.


Figure 4. Evolution ofRing-necked Parakeet po-pulation based on counts atthe sole Brussels roost.

Figure 5. Evolution of someindigenous hole-nestersover the period 1992-2001(Weiserbs et al. 2002).

Waterbirds

There are six alien waterbirds, of which only the Mute Swan has been present for along time – over 100 years.Mute Swan. This species was common in captivity in Brussels from the 19th centuryonwards (Rabosée 1995). The city’s population is fairly stable, with 30-40 individu-als and about ten nesting pairs. Occasional interactions with indigenous waterbirds,including destruction of nests of Great Crested Grebes and Coots have been reported.

Black Swan. This ornamental species has been introduced into at least three parks:the Royal Park, de Karreveld Castle and the Marie-José Park. The first record ofbreeding was in 2002, however the young birds died during the winter.

Magellan Goose. The Brussels population comes from the Royal Park, the only nest-ing site for the species at the beginning of the 1990’s. Since 1996, nesting has increasedin the public parks. In 2001, 55 individuals were counted in the Royal Park, but nest-ing was not recorded. Elsewhere in the city, the population varies around ten nestingpairs. The potential threat of this species to indigenous species seems to be very low,since it is not very aggressive and its reproductive rate is low: the proportion of nest-ing birds is surprisingly small and most of the time there are only one or two young pernest, sometimes 4-5.

Canada Goose. This species is increasing rapidly in Belgium; numbers reached about4000 at the beginning of 2002, 80 % being in Flanders. The colonisation of Brabant(centre of Belgium) took place from the Flanders (north part of Belgium); however,there are limited interchanges with birds from the south of the country, as shown byrecoveries of birds marked in the Brussels suburbs. The species attempted to breed fora few years at the Royal Park. In 2003, five breeding pairs were noted in public parks.

Egyptian Goose. This species has been breeding in the wild in the Brussels Regionsince 1984 (Rabosée 1995). At the beginning of the 1990’s, 27 breeding pairs werecounted. The present population in Brussels comprises about 40 breeding pairs. Inaddition there are several groups of non-breeding birds – sometimes a few dozen dur-ing the breeding season. The regional population is largest during the winter (210-250 birds in January since 1997).

Waterbird monitoring in Brussels since 1992 has provided information regardingthe possible effects of this species on indigenous species (Weiserbs & Jacob 2000b).This monitoring involves annual sampling at 20 principal Brussels wetlands.Development of each species has been analysed in relation to the abundance ofEgyptian Geese. No trends have been detected over the period 1992-2000 (Figure 6:for example Coot). This could be explained by the fact that the densities of EgyptianGeese at each site remain low and that there are sufficient resources to ensure thereis no or very little competition.

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Mandarin Duck. This species has been breeding in the wild in Brussels since 1989(Rabosée 1995). Since then, the population has been slowly increasing. In 1999 thepopulation was estimated at 20-25 individuals (De Schutter et al. 1998), distributedamong wooded wetlands and urban parks. A discreet hole-nester, this species doesnot seem to represent a potential threat to the indigenous avifauna.

Other Alien Species. The Pheasant survives in small numbers in the open countrysidein the peripheral areas of the city. Up to the 1960’s the species was very common asthe result of the large numbers released for shooting purposes. The abolition of shoot-ing led to the cessation of restocking and of artificial feeding, which explains itssteady decline.

The Feral Pigeon established itself during the first half of the 20th century. Thisis one of the most common species in the intensively built-up areas. However, itsecological niche is very different from those of the other urban birds and no negativeeffects have been observed. On the other hand, their droppings are a major problemfor the city’s buildings (Rabosée 1995).

Anecdotes/observations

The avifauna of the city of Brussels is influenced in several ways by the behaviourof the city’s inhabitants. For example, the abundance of food provided by people con-


Figure 6. Evolution of Coot in relation to the abundance of Egyptian Geese at 20 main wetland sites in Brussels.

stitutes a vital factor, not only for some species, but also for the habitats. In thisrespect, the wetlands in the city parks particularly suffer from this input of food,which is at least partly responsible for the ravages caused by botulism. Artificialfeeding has a strong influence on the familiarity of the waterbirds. During duck cen-suses telescopes are often useless, because all the birds come right to the observer’sfeet to beg for bread. Some other species are also less fierce than they are outside thecity, for example Grey Herons,Woodpigeons and Carrion Crows will allow people toapproach to within a few metres. The parakeets also benefit widely from this supplyof food; in particular it is assumed that it allows the Monk Parakeet to survive in thevery centre of the city. The public kindness towards this species was illustrated in1985 when the people in one neighbourhood purchased a chimney which was due tobe destroyed and which held the parakeets' first communal nest. The nest finally felldown in 2002 because of its weight.

CONCLUSIONS

The development of the Brussels avifauna is linked to a large extent with the processof urbanisation and with the resulting alterations to natural habitats. The majority ofgreen spaces in Brussels have been subjected to major modifications and manage-ment and some have completely disappeared. During the last century, many indige-nous species associated with the most vulnerable habitats have disappeared, namelyspecies of woodlands, wetlands and waste land. In total, 20 to 22 species have dis-appeared from the Brussels region and other species are undergoing severe declines.Most often, these species are also declining on a larger scale, but the decrease is oftenmore severe in Brussels than elsewhere in Belgium. Some species have shown wor-rying declines over the last fifteen years; this trend includes species that were onceconsidered to be widespread and common. In addition, new indigenous speciesappeared in Brussels, mostly species that are increasing in Belgium or elsewhere inEurope. Thus their appearance does not result from any favourable habitat modifica-tions but rather from adaptation to new climatic conditions and new environments.The increase of some other species may be explained by a decline of human pressure,including direct effects (such as hunting) and indirect effects (such as the use of pes-ticides, which are particularly harmful to birds). The medium-term prospects forother species that are still abundant are unknown as a result of insufficiently accuratehistorical data: Swift and Black Redstart for example, two birds for which a townsuch as Brussels constitutes an important population nucleus. Finally, the urban envi-ronment is particularly favourable for a small number of generalist and/or anthropicspecies, which constitute the majority of the Brussels avifauna.

Hence, in general, the indigenous avifauna tends to decline whilst those speciesthat are particularly adapted to urban habitats increase. The increase and spread ofalien species have been particularly striking over the past fifteen years. This gives an

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additional signal of an overall degradation of the avifauna. This is worrying in manyrespects, particularly in the context of the widespread urbanisation of the central partof Belgium. A reduction and deterioration is observed in areas favourable for some-what specialised species which cannot tolerate disturbance or various hazards, suchas poor air quality, high ambient noise, site fragmentation, high density of domesticand/or anthropophilic predators. The built-up regions could therefore become mar-ginal and increasingly poor in species. Only national measures bringing together theenvironment and nature can stop this process.

WHERE TO WATCH BIRDS

Marais de Jette-Ganshoren Jette – Ganshoren marshesHof ter MuschenRéserve naturelle du Moeraske – Moeraske Nature ReserveScheutbosGrand étang de Boitsfort – Boitsfort Lake/PondForêt de Soignes (Vallée du Vuylbeek, Rouge-Cloître) – Soignes Forest (Vuylbeek

Valley, Rouge- Cloître)Cimetière de Bruxelles – Brussels Cemetery

ACKNOWLEDGEMENTS

Since 1992, the monitoring of the Brussels avifauna by AVES has been included within the framework ofthe Brussels Environment Survey. This is financed by the Brussels Region and is organised by the BrusselsInstitute for Environmental Management (IBGE-BIM). We thank them for their support.

We warmly thank the volunteers from AVES who take part in the field surveys. Several aspects of themonitoring programme, including the new Breeding Bird Atlas, depend on their enthusiasm.

REFERENCES

de Schaetzen, R. & Jacob, J.-P. (1985). Installation d’une colonie de Perriches jeune-veuves (Myiopsittamonachus) à Bruxelles. Aves 22, 127-129.

de Schutter, G., Weiserbs, A. & Jacob, J.-P. (1998). Le suivi de l’avifaune en tant que bioindicateur de l’é-tat de l’environnement en Région de Bruxelles-Capitale. Pages 117-130 in Qualité de l’Environnementet Biodiversité en Région de Bruxelles-Capitale. Bruxelles, Documents de travail de l’Institut Royal desSciences Naturelles de Belgique.

Devillers, P., Roggeman, W., Tricot, J., Del Marmol, P., Kerwijn, C., Jacob, J.-P. & Anselin, A. (1988).Atlas des oiseaux nicheurs de Belgique. Bruxelles, Institut Royal des Sciences Naturelles de Belgique.

Jacob, J.-P. (1992). Projet de surveillance de l’environnement par bioindicateurs en Région bruxelloise.Possibilités d’utilisation de l’avifaune. Document de travail, Aves, 1-40.

Jacob, J.-P. & Paquay, M. (1992). Oiseaux nicheurs de Famenne. L’Atlas de Lesse et Lomme. Aves, Liège.Juniper, T. & Parr, M. (1998). Parrots. A Guide to the Parrots of the World. Pica Press Sussex.Onclincx, F. & Desager, M. (1997). Etat de l’Environnement en Région de Bruxelles-Capitale. Hannequart

& Schamps Eds. Bruxelles, 1-48.Rabosée, D. (Ed.) (1995). Atlas des oiseaux nicheurs de Bruxelles 1989-1991. Aves, Liège, 1-304. Saintenoy-Simon, J. (1998). Etude de la flore de la région de Bruxelles-capitale. In: Qualité de


l’Environnement et Biodiversité en Région de Bruxelles-Capitale, 43-66. Bruxelles, Documents de tra-vail de l’Institut Royal des Sciences Naturelles de Belgique.

Scaillet, C. (1999). Etude de l’adaptation et de l’impact de la Perruche à collier Psittacula krameri enmilieu urbain bruxellois – Mémoire de fin d’étude.

Weiserbs, A. & Jacob, J.-P. (1996). L’hirondelle de fenêtre Delichon urbica en 1996 en région bruxelloise.Aves 33(4), 261-262.

Weiserbs, A. & Jacob, J.-P. (2000a). Etude de la population de Perriche jeune-veuve (Myiopsittamonachus) à Bruxelles. Aves 36, 207-223.

Weiserbs, A. & Jacob, J.-P. (2000b). Surveillance de l’Etat de l’Environnement Bruxellois. Groupe deTravail Aves. Rapport 2000, 1-100.

Weiserbs, A. & Jacob, J.-P. (2001). Surveillance de l’Etat de l’Environnement Bruxellois. Groupe deTravail Aves. Rapport 2001, 1-65.

Weiserbs, A., Janssens, M. & Jacob, J.-P. (2001). Une troisième perruche nicheuse en Région bruxelloise:la Perruche alexandre Psittacula eupatria. Aves 37(3-4), 115-120.

Weiserbs, A., Jacob, J.-P. & Vansteenwegen, C. (2002). Résultats de dix années de surveillance de l’avi-faune nicheuse par points d’écoute à Bruxelles. Poster.

Weiserbs, A. & Jacob, J.-P. (in prep). Surveillance de l’Etat de l’Environnement Bruxellois. Groupe deTravail Aves. Rapport 2002.

Authors’ address:Anne Weiserbs & Jean-Paul Jacob, Société d’études ornithologiques AVES, c/o 3 rue Fusch, B - 4000Liège. [email protected], [email protected]

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APPENDIX

Table 3. Summary of changes in the indigenous breeding avifauna during the 20th century. E: extinct in 2004; NE: nearly extinct in 2004; ?: doubtful

>1940 1940-60 1961-68 1973-77 1989-91 1992<

Barn Owl - Tyto alba + + + + + +Black Redstart - Phoenicurus ochruros + + + + + +Black Woodpecker - Dryocopus martius + + + + + +Blackbird - Turdus merula + + + + + +Blackcap - Sylvia atricapilla + + + + + +Blue Tit - Parus caeruleus + + + + + +Bluethroat - Luscinia svecica + (?) + - - - -Bullfinch - Pyrrhula pyrrhula + + + + + +Buzzard - Buteo buteo + + + (?) + (?) + +Carrion Crow - Corvus corone + + + + + +Cetti's Warbler - Cettia cetti - - - + (?) - -Chaffinch - Fringilla coelebs + + + + + +Chiffchaff - Phylloscopus collybita ? + + + + +Cirl Bunting - Emberiza cirlus + + - - - -Coal Tit - Parus ater + + + + + +Collared Dove - Streptopelia decaocto - + + + + +Coot - Fulica atra + + + + + +Corn Bunting - Miliaria calandra + + + + - -Crested Lark - Galerida cristata + + + + - -Crested Tit - Parus cristatus - + + + + +Crossbill - Loxia curvirostra ? ? + (?) + (?) + (?) + Cuckoo - Cuculus canorus + (?) + + + + + (NE)Dunnock - Prunella modularis + + + + + +Fieldfare - Turdus pilaris - - - - + +Firecrest - Regulus ignicapillus ? + + + + +Garden Warbler - Sylvia borin ? ? + + + + Goldcrest - Regulus regulus - (?) + + + + +Golden Oriole - Oriolus oriolus ? + + + + + (NE)Goldfinch - Carduelis carduelis + + + + + +Goshawk - Accipiter gentilis + + + - - +Grasshopper Warbler - Locustella naevia ? ? - (?) + (1981) + (?) + (E)Great Crested Grebe - Podiceps cristatus - - - + + +Great Grey Shrike - Lanius excubitor + + - - - -Great Reed Warbler - Acrocephalus arundinaceus + + + - - -Great Spotted Woodpecker - Dendrocopos major + + + + + +Great Tit - Parus major ? ? + + + +Green Woodpecker - Picus viridis + + + + + +Greenfinch - Carduelis chloris ? + + + + +Grey-headed Woodpecker - Picus canus + (?) - - - - -Grey Heron - Ardea cinerea - - + + + +Grey Wagtail - Motacilla cinerea ? ? ? + + +Hawfinch - Coccothraustes coccothraustes + + + + + +Hobby - Falco subbuteo - ? + + + +Honey Buzzard - Pernis apivorus - - - - - (?) +Hoopoe - Upupa epops + + - - - -House Martin - Delichon urbica + + + + + +House Sparrow - Passer domesticus ? ? + + + +Icterine Warbler - Hippolais icterina + + + + + +Jackdaw - Corvus monedula + + + + + +Jay - Garrulus glandarius + + + + + +Kestrel - Falco tinnunculus - + + + + +Kingfisher - Alcedo atthis + + + + + +Lapwing - Vanellus vanellus - - - + + +Lesser Grey Shrike - Lanius minor + (1874) - - - - -Lesser Spotted Woodpecker - Dendrocopos minor + + + + + +Lesser Whitethroat - Sylvia curruca + + + + + +Linnet - Carduelis cannabina ? ? + + + +


Little Bittern - Ixobrychus minutus + (>1890) - - - - -Little Grebe - Tachybaptus ruficollis ? + + + + +Little Owl - Athene noctua + + + + + +Little Ringed Plover - Charadrius dubius ? ? ? + + +Long-eared Owl - Asio otus ? + + + + +Long-tailed Tit - Aegithalos caudatus ? ? + + + +Magpie - Pica pica + + + + + +Mallard - Anas platyrhynchos + + + + + +Marsh Tit - Parus palustris ? + + + + +Marsh Warbler - Acrocephalus palustris + + + + + +Meadow Pipit - Anthus pratensis + + + + + + (NE)Middle Spotted Woodpecker - Dendrocopos medius - - - - - +Mistle Thrush - Turdus viscivorus + + + + + +Moorhen - Gallinula chloropus + + + + + +Nightingale - Luscinia megarhynchos + + + + + +Nightjar - Caprimulgus europaeus + (?) ? + + - -Nuthatch - Sitta europaea + + + + + +Ortolan Bunting - Emberiza hortulana + - - - - -Partridge - Perdix perdix + + + + + +Peregrine - Falco peregrinus + (?) - - - - +Pied Flycatcher - Ficedula hypoleuca + - - - - -Pochard - Aythya ferina - - - + (1979) + -Quail - Coturnix coturnix + + + + - -Red-backed Shrike - Lanius collurio + + - - - -Redstart - Phoenicurus phoenicurus + + + + + + (NE)Reed Bunting - Emberiza schoeniclus - + + + + + (?)Reed Warbler - Acrocephalus scirpaceus + + + + + +Robin - Erithacus rubecula + + + + + +Rook - Corvus frugilegus + + + - - +Sand Martin - Riparia riparia + + + + - -Savi's Warbler - Locustella luscinoides ? + + (?) - - -Sedge Warbler - Acrocephalus schoenobaenus + + + - - -Serin - Serinus serinus + + + + + +Short-toed Treecreeper - Certhia brachydactyla + + + + + +Siskin - Carduelis spinus + + + + + + (?)Skylark - Alauda arvensis + + + + + + (NE)Song Thrush - Turdus philomelos + + + + + +Sparrowhawk - Accipiter nisus + + + + (?) + +Spotted Flycatcher - Muscicapa striata + + + + + +Starling - Sturnus vulgaris + + + + + +Stock Dove - Columba oenas + + + + + +Stonechat - Saxicola torquata + + + + + + (E)Swallow - Hirundo rustica + + + + + +Swift - Apus apus + (?) + + + + +Tawny Owl - Strix aluco + + + + + +Tree Pipit - Anthus trivialis + + + + + + (E)Tree Sparrow - Passer montanus ? ? + + + +Tufted Duck - Aythya fuligula - - - - + (1981) +Turtle Dove - Streptopelia turtur + + + + + + (E)Water Rail - Rallus aquaticus + + + + - -Wheatear - Oenanthe oenanthe + (?) - - - - -Whinchat - Saxicola rubetra + + - - - -White Wagtail - Motacilla alba + + + + + +Whitethroat - Sylvia communis + + + + + +Willow Tit - Parus montanus ? ? + + + +Willow Warbler - Phylloscopus trochilus + + + + + +Wood Warbler - Phylloscopus sibilatrix + + + + + + (E)Woodchat Shrike - Lanius senator + (?) - - - - -Woodcock - Scolopax rusticola - (?) + + + + +Woodlark - Lullula arborea + (1859) - - - - -Woodpigeon - Columba palumbus + + + + + +Wren - Troglodytes troglodytes + + + + + +Wryneck - Jynx torquilla ? + + - - (?) -Yellow Wagtail - Motacilla flava + + + + + + (NE)Yellowhammer - Emberiza citrinella + + + + + +

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