Stenskvättants Oenenthe oenanthe rastning på Helgoland: var förenas och klyvs flyttvägarna för skandinaviska och nearktiska fåglar?

Abstract

According to measurements from bird ringing, Northern Wheatears of both Scandinavian (subspecies oenanthe) and Nearctic (subspecies leucorhoa) origin stopover on Helgoland (southeastern North Sea) during spring and autumn migration. Although with a large overlap, leucorhoa birds migrate earlier in spring and later in autumn compared to oenanthe. In release experiments during spring migration, Scandinavian birds headed in directions between northwest and northeast, while Nearctic birds departed in directions between southwest and north. Most Nearctic Wheatears are assumed to switch their direction to northwest already west of Helgoland, some do this on Helgoland but some continue on a northerly course and then head northwestwards in southern Norway. Only very few leucorhoa birds occur east of Helgoland in spring as well as in autumn (shown by birds captured at Greifswalder Oie, 390 km east of Helgoland). Some long-winged Wheatears are found much further east at Rybachy (Courish Spit), most probably belonging to Siberian breeding populations. Owing to the gap in the occurrence of long-winged Wheatears in the western Baltic it is unlikely that long-winged individuals at the German North Sea coast are of Siberian origin.