IMIS - Marine Onderzoeksgroepen

The data is collected to discover trends in long term breeding bird occurrences in Flanders and is used for the EU reporting on trends, distribution and future prospects of the species listed in the Annex 2 and 4 of the Habitats Directive.
Sampling methods: The atlas of breeding birds in Flanders (https://www.gbif.org/dataset/81c5a091-6e94-40db-a2a4-48f4de42d410) was based on territory mapping in 5×5 km UTM-squares with additional information collected in a subset of 8 1×1 km squares (Vermeersch et al., 2004). So, since we already had information in over 5,000 1×1 UTM-squares, we chose that grid as a basis for the new census. The grid was then randomly stratified over 6 habitat types (farmland, woodland, urban, suburban, heathland and marshland) and finally,6 points were randomly assigned to each grid cell (Fig. 1). Each point has to be counted three times in a year in predefined periods (DD/MM): 01/03-15/04, 16/04-31/05 and 01/06-15/07. All six points in a square have to be counted on the same day and subsequent counts of the same points in different periods should lie apart for at least two weeks. A separate study (Onkelinx et al., 2006) was carried out to estimate the sample size needed to calculate good indices for the majority of common species. The study was based on density-figures in 1×1 km squares from the previous atlas. Finally, 1200 squares were randomly chosen from the above mentioned grid. Considering the number of volunteers and to increase geographical coverage and sample size, we chose for a three-year cycle. Initially, every point had two observation circles around it (50 and 150 meters), but after consulting our Dutch colleagues from SOVON, we chose not to use these circles. Instead, this system is preserved for a calibration study in 10 % of all squares that should allow us to calculate density functions for some of the commoner species (see also Van Turnhout, 2006). In this study, all observations will be drawn on a map, while in the ‘normal’ scheme this is not requested. This fieldwork is carried out by INBO staff. The voluntary network Starting from the existing network in the BBV-project, approximately 40 regional coordinators were found throughout Flanders. Natuurpunt and INBO started giving lectures about the project and its methodology in March. Although this was a rather late start, volunteers were very eager to join in and after a few weeks, over 300 squares (for 2007) were already assigned to approximately 150 different people. For the following years, success will be even higher since some regional groups chose to start only next year. All volunteers received maps, field forms and a methodology folder (Bird Census News 2007: 20/1).