Status quo of verandering? Zeearenden in Nederland in 1945-1997

The White-tailed Eagle is a scarce wintering bird in The Netherlands. In 1945-1978 the annual number of wintering White-tailed Eagles varied between one and four. Since the severe winter of 1978/1979, average wintering numbers are slightly higher, although they show considerable annual fluctuations (figure 1). Nowadays, up to ten or more White-tailed Eagles may be present in The Netherlands. The winter distribution has changed somewhat in the course of time (figure 2). In the 1940s and early 1950s Whitetailed Eagles regularly occurred on vast heathlands in the centre of the country (Veluwe), where they fed on Rabbits and remnants of deer hunting. The eastern coasts of Lake Ijsselmeer were regularly visited as well. In the 1960s and early 1970s inland observations showed some emphasis on the south and southeast of the country, whereas the centre had lost its significance for wintering eagles. In 1976-1986 the newly reclaimed polders of Lake IJsselmeer attracted huge numbers of waterfowl and became a regular wintering area for White-tailed Eagles, especially the Oostvaardersplassen area. However, since then the number of waterfowl decreased in the polders as did the number of White-tailed Eagles. Since 1986, growing numbers of wintering eagles visit the northern part of the Delta area (Haringvliet, Hollandsch Diep, Biesbosch) in the southwest of the country. In The Netherlands, the White-tailed Eagle is a typical winter bird, the first birds normally showing up in October. Wintering numbers are highest in January. In March most eagles have left the country (figure 3). In earlier years (1945-1960), maximum numbers were recorded earlier, in November, This peak may have been caused by birds migrating through but wintering outside the country. White-tailed Eagles occurring in The Netherlands are mainly birds in juvenile or immature plumage (>95%). Ringing recoveries show that the birds originate from North and Central Europe (Germany: n=2, Finland: n=2, Nonway: n=1). The breeding populations in those areas have increased strongly in the last decade or so, and the breeding range has expanded westward. Denmark and Lower-Saxony (Germany) have been colonised quite recently whereas the breeding population in Schleswig-Holstein (Germany) has increased rapidly. As a result, numbers of wintering White-tailed Eagles in these areas have exploded in the 1990s. In The Netherlands the number of wintering birds has not (yet) changed dramatically within the last decade. Apparently, for White-tailed Eagles our country is still at the outskirts of their wintering area. In this, the situation shows similarities to that in Belgium and France. It is expected, however, that in future years The Netherlands will welcome more wintering White-tailed Eagles as a result of an ongoing population increase and range extension, perhaps stimulated by the planned reduction of winter feeding programmes in northern countries as well.