Perspectives in using shorebird counts for assessing long-term changes in wader numbers in the Wadden Sea

Abstract

Over the past 20 years, a tradition has developed in western Europe of carrying out shorebird surveys in estuaries. These counts are mostly conducted by amateur ornithologists, usually well acquainted with the area in which they are active. The results of these surveys are well reproducible for at least the abundant species, and information is available on the size of the errors which occur. In several parts of Europe, shorebird surveys have been carried out long enough to allow trend analysis of population size. Four examples from Great Britain demonstrate that monitoring schemes may also be used for management purposes, especially if combined with specific research projects. Long-term shorebird surveys can be used not only for simple analysis of trends in bird numbers, but also to provide a deeper understanding of the functioning of the ecosystem. They may also act as a tool to document the effects of management activities in the area concerned. Shorebird surveys in the Wadden Sea have not only revealed the extremely large importance of the area, especially for waders, but also show that different areas are exploited in different ways. They have also provided data on changes in bird numbers throughout the year. Apart from the counts carried out in January, the frequency of counts in most areas in the Wadden Sea has been too low to allow the results to be used for monitoring purposes. In an area as large as the Wadden Sea, some sites, often supporting large numbers of birds, may not always be covered during simultaneous surveys. This may seriously affect the completeness of the count. The best way to overcome this problem is to calculate index values, using only those sites which have been surveyed in successive years. Two monitoring schemes are proposed which may be effective in providing relevant information for management purposes. © 1989 Biologische Anstalt Helgoland.