From the winter of 2012/13 until the breeding season of 2015, fieldwork for a new Dutch bird distribution atlas will be carried out, of which the basic methodology is described here. Aims of the new atlas are to provide an up to date and comprehensive description of bird distribution, both in the breeding season and in winter, in a more quantitative way (absolute instead of relative densities) and with greater spatial resolution than achieved in previous atlases, and to evaluate changes in distribution since these (breeding birds 1973-1977 and 1998-2000, year-round 1978-1982).
In order to maintain comparability with previous atlases, the general design of data collection combines assembling an comprehensive list of species present in each atlas square (5x5 km) with more standardised and quantitative observations in eight of the 25 1x1 km quadrats per square (fig. 1). Fieldwork in the quadrats consists of one hour visits in each of two six-week periods per season, during which all species observed are recorded, as well as observed numbers of a selection of relatively scarce species. Part of each hourly visit is a five-minute point count in the centre of the quadrat, during which all individuals are counted. In a facultative extended version of this point count all bird observations are mapped and the count is repeated in immediate succession.
All observations of rare species and previously unknown breeding colonies, in both the quadrats and the general atlas squares, are recorded on digital maps. Data entry for this project will take place entirely via internet.
To obtain quantitative distribution (density) maps for breeding birds, the quadrat data will be combined with density information obtained by territory mapping in well over 1500 plots across the country (mainly from the national breeding bird monitoring scheme) and geo-information on habitat characteristics (fig. 2). Winter density maps of terrestrial species will be based on hierarchical modelling of the extended point count data (figs. 3,4), while the distribution of waterbirds will be quantified mainly on the basis of comprehensive long-term count data, combined with density estimates for areas not counted. In this design, data collected in all bird monitoring schemes run by Sovon (including territory mapping, point and site counts) contribute to the atlas project.
Schekkerman H., van Turnhout C., van Kleunen A., van Diek H. & Altenburg J.
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