Birds in Wallonia: new maps available
Birds are good indicators of the health of all biodiversity. It is therefore essential to study bird population trends to identify changes in other taxonomic groups. Understanding the factors impacting bird populations makes it possible to take action in favour of biodiversity.
Bird populations have been showing many changes for a long time. In Europe, for example, the Farmland Bird Index (FBI) has been used since 1990 to inform us about biodiversity trends related to agricultural environments. This index is based on population trends of 39 bird species. In 30 years, the FBI has shown a decrease of more than 30%. Wallonia is no exception. Indeed, since 1990, the index, based on 15 species, has also shown a sharp decrease. Among the 15 species, only one species shows a significant increase in recent years. In agricultural environments, several explanations have been identified, such as the loss of hedges, land drainage, increased mechanization and increased use of pesticides and fertilizers.
Thomas Coppée, a doctoral student at the BP unit, is studying bird population trends using modelling tools and environmental data produced as part of the LifeWatch-WB project. The objective is also to understand the factors impacting changes in bird populations.
How to develop density maps?
The analysis of bird population trends is based on 2 ornithological data sets available for two periods (2001-2007 and 2015-2018). These datasets come from inventories coordinated by Natagora-Aves, which uses a large number of amateur ornithologists. These inventories consist of covering 1 km² squares twice (25/03 - 30/04 and 15/05 - 30/06) for one hour. All birds are recorded, with the exception of non-breeding migratory birds. Two behaviours are noted: breeding birds (song, breeding indications...) and simple presence (feeding, rest,...).
To explain the observed trends, an environmental data set is available for each period. These data are from the ecotope database produced by the LifeWatch-WB project. The database contains several types of data related to land use, topography, soil and climate. Land use data are obtained by a pixel classification of Wallonia's orthophotos (2006-2007 and 2015).
Generalized Additive Models (GAMs) are used to study trends. The inventory method allows the use of abundance data with absences. Indeed, if a species has not been observed during the two passages in the square, this species is considered as absent. Several methods of model construction are used. The models make it possible to predict the size of populations on the scale of Wallonia and to obtain density maps. The calculated trends are then compared with an independent data set (survey of monitoring of common birds in Wallonia).
To go further
All the maps produced are put online on a website. Maps are available for both inventory periods (2001-2007 and 2015-2018). This makes it possible to observe global and local changes in Wallonia. A descriptive text is associated with each species. Species are added to the website as they become available.
Ruedi Aeschlimann, Nicolas Dory, Nature Ariège, Mathias Schäf, Aurélien Audevard, Marcel Burkhardt, Andreas Trepte, Jenny Jones, Jean-Louis Coppée, Thomas Coppée