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Evolution of avifauna
According to the latest atlas of breeding birds of the Brussels-Capital Region (2000-2004) there are 103 bird species (including 11 foreign species) that build their nests in the Brussels-Capital Region. Only 16 of these – mainly opportunistic – bird species can be considered to be widespread. Over the past decades the local avifauna has decreased, but a few positive trends have been observed as well: a return or increase of remarkable nesting bird populations, and an increase of various native species (including, especially, the swallow). Moreover, thanks to the annual monitoring of common breeding birds, the trend for the period 1992-2011 could be determined for 36 species. For 12 of these species (including 2 foreign species) the number of birds increased; for 10 species the population remained stable, for 14 a decrease was recorded.
These birds are excellent biodiversity indicators. Their remarkable ability to spread out enables them to react quickly to changes in the environment. In addition, they are present in most biotopes and represented at practically all levels of the food chain, also at the highest levels (insectivores, predators). They are also easy to observe.
The monitoring of the Brussels avifauna takes place in different ways: via the preparation of an atlas which provides an overview of the distribution and numbers of nesting birds (every 10-20 years), the monitoring of the avifauna as a whole or of specific groups, specific scientific studies, etc. This monitoring is performed mainly by the non-profit organisation AVES at the request of Bruxelles Environnement-Leefmilieu Brussel.
The atlas of breeding birds
The most recent atlas of breeding birds of the Brussels-Capital Region, which refers to the period 2000-2004, mapped 103 species (including 11 non-native species), which corresponds to around half of all nesting species in Belgium. Of these species only 16 can be considered to be widespread. These are mainly opportunistic species which are able to adapt to an urban environment (certain songbirds, wood pigeons, black crows, etc.); species that have higher ecological demands are usually rarer.
Based on an analysis of the historical data for the Brussels-Capital Region the authors of the atlas were able to demonstrate that thorough changes had taken place, both in breeding densities and in the species composition:
- the average number of species per km2 had decreased, from 36.1 in 1989-1991 to 33.7 in 2000-2004;
- 14 species had recently disappeared – or nearly so, both at the level of the Region and at the level of the province of Brabant;
- around fifteen species connected to open and semi-open environments (fields, brushwood, etc.) disappeared between 1944 and 2004;
- the number of non-native nesting species had increased considerably and the populations of certain foreign species were growing exponentially (parakeets).
These negative trends are mitigated somewhat by the return or appearance of remarkable breeding birds (goshawk, middle spotted woodpecker, peregrine falcon) and by the growing numbers of several native species that benefit from more favourable or more common biotopes (i.e. parks and gardens) and management measures that are better adapted to natural environments or protection measures. For instance, since 2003 we have observed a rise in the house martin population – after a dramatic decline – which may be related to the various campaigns held to encourage the placing of nesting boxes in some Brussels municipalities. In 2012 the house martin population comprised 299 pairs – which is a lot more than in 1992 – whereas in 2002 no more than 33 pairs were counted.
Annual monitoring of common breeding birds
The annual monitoring of common breeding birds has been organised since 1992. This takes place via the 'listening point' method, which consists in making an inventory in spring of all birds that are seen or heard in a period of 15 minutes. According to this method, which is suitable mainly for species that mark their territory by singing, nearly a third of the Brussels avifauna is being monitored. Today, the network of listening points comprises 114 stations; these represent both the strongly varying green spaces in the Brussels area and the densely developed environments.
For the period 1992-2011 a trend could be observed for 36 species (namely for those with which regular 'contacts' can be recorded, i.e. the most widespread species of the Brussels-Capital Region): 12 of these species (including 2 foreign species) have improved, 10 species have remained stable, and 14 species have declined.
Trends in the evolution of common breeding birds in the Brussels-Capital Region (1992-2011)
Source: Weiserbs A., Lebeau O. & J.-Y Paquet, 2012 (AVES)
The green colour indicates species that improved, the blue colour species that remained stable, the red colour species that declined (average annual percentages, the error flag marks the confidence interval around the trend).
According to AVES, of all breeding birds, the decline seems to be greatest among migratory birds (marsh warbler, whitethroat, etc.). The loss of and damage to their habitats in the wintering areas is one of the hypotheses that have been suggested to explain this trend. A positive evolution – i.e. an increase in the populations, on the other hand, has been observed for Corvidae (jay, magpie, jackdaw, crow), hole-nesting native species (nuthatch, green woodpecker, spotted woodpecker, bluetit and great tit, robin and short-toed tree creeper), and species that have a connection with buildings (pigeons, etc.). After a strong decline in the 1990s and early 2000s house sparrow populations have significantly increased since 2003.
- WEISERBS A, PAQUET J.Y, GOSSE D, ALVAREZ M.C. 2012. Inventaire et surveillance de l’avifaune – final report 2012, Brussels, study performed by Aves for Bruxelles Environnement-Leefmilieu Brussel, 34 pages + appendices
- WEISERBS A. & JACOB J.-P. 2007. Oiseaux nicheurs de Bruxelles 2000-2004: répartition, effectifs, évolution, Liège, study commissioned by Bruxelles Environnement-Leefmilieu Brussel, 292 pages.