Locally adapted migration strategies? Comparing routes and timing of northern wheatears from alpine and lowland European populations

The northern wheatear Oenanthe oenanthe has an almost circumpolar breeding distribution in the Northern Hemisphere, but all populations migrate to sub-Saharan Africa in winter. Currently, tracking data suggest two main access routes to the northern continents via the Middle East and the Iberian Peninsula. These routes would require detours for birds breeding in the European Alps. Our aim was to map the migration routes and determine annual schedules for birds breeding in Switzerland and Austria, using light level geolocators. We compared their migration patterns with birds from a lowland breeding population in Germany. Birds from the Alps cross the Mediterranean Sea directly heading straight to their non-breeding sites. In contrast, birds from Germany travelled further west via the Iberian Peninsula. While the German population initiated autumn migration relatively early, arrival on the wintering sites was nearly synchronous across the three populations. During spring migration, German birds arrived earlier at their breeding grounds than birds from the Alps. A comparison with the literature indicated that the breeding populations in the Alps use their own route and are among the latest to arrive in spring, showing resemblance to the phenology of Arctic breeding populations. Our results indicate that the annual cycle of Alps-breeding wheatears is influenced primarily by breeding ground conditions, and not solely by migration distance.