VERSTRAEL T, MEIJER R & DAEMEN B (1990) The accuracy of the Common Breeding Bird Census sample. LIMOSA 63 (4): 153-160.

The Dutch Common Breeding Bird Census (BMP, Breeding Bird Monitoring Project) has developed into a successful project, with 600 plots being censused within five years after its start. The major goal of the project is to monitor changes in population size and distribution of common breeding bird species in The Netherlands. To be able to reach this goal conditions concerning sample distribution over habitats and regions have to be met. An analysis of BMP-data from the period 1984-88 shows that urban and agricultural areas are notably underrepresented in the BMP-sample, relative to the nationwide portions of these habitats. On the other hand, dry natural habitats, such as dunes and heaths as well as woods and parks, are overrepresented in the sample. In addition, a large part of the data from the dune, heath and marsh habitats are collected in only three study areas. Up to and including 1988, the BMP yielded sufficient data to calculate reliable indices for 60 species. For 27 additional species, the uneven composition of the sample prevented this, although sample sizes were sufficiently large. In the future these problems may be solved by starting more plots in urban and agricultural areas and by weighing the results. Since certain habitats are censused very intensively it will soon be possible to calculate indices for The Netherlands as a whole as well as for various habitats. This will considerably improve the value of this project.

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