| Titre : | [Occurrence of raptors on Helgoland (German Bight, North Sea): Regular migration or wind drift?] |
| Auteurs : | Volker Dierschke, Auteur |
| Type de document : | Article |
| Dans : | Vogelwelt (Die) (122(5) 2001) |
| Article en page(s) : | 247-256 |
| Résumé : | On the North Sea island of Helgoland (50 km off the German Wadden Sea coast), ten raptor species occur as regular migrants, with more or less regular presence of some species in summer (Kestrel, Northern Harrier) and winter (Sparrowhawk, Common Buzzard, Kestrel). High birdwatching activity in the 1990s provided insights into the migration patterns of species which were formerly believed to be rare on the island. However, the occurrence of raptors is strongly influenced by wind conditions. Most raptors were seen while winds were from southeast or east, apparently blowing the birds off the coastline which they usually follow. This effect was most pronounced in the larger species which migrate by soaring, but was less important in smaller species (Sparrowhawk and falcons) migrating by flapping flight. Therefore, larger species seem to reach Helgoland mostly due to wind drift, while especially Sparrowhawk and Merlin seem to cross the German Bight intentionally. Part of the raptors passing the island flew to directions possibly related to correction for wind drift. In autumn this was true especially for the soaring migrants Honeybuzzard and Common Buzzard. No age effect on wind drift was detected as the percentage of immature birds resembled that observed at Falsterbo (Sweden). The relatively late spring passage of Osprey and Marsh Harrier in May, however, might be attributed to late migrating nonbreeders. In other species, seasonal patterns of occurrence on Helgoland corresponded to those found at the nearby mainland (northern Germany, Denmark). |
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