Geolocator tagging of east Siberian bluethroats

Many long-distance migratory bird species seem to retain the winter quarters their ancestors used during the last glacial maximum. Post-glacial colonization following the retreat of the ice sheets have then resulted in apparent suboptimal migration routes, since the expanding populations have failed to use more nearby, alternative and climatically suitable, wintering areas. The bluethroat subspecies Cyanecula svecica svecia occurs in the northern areas of the Palearctic from the Atlantic to Alaska. Because it is monotypic and lacks population structure in mitochondrial DNA it is assumed to have colonized its present range from one glacial refuge population. Geolocator tracks from birds in its western range have shown that these migrates to the Indian subcontinent following a route west of the Himalaya. In the present study we fit geolocators of bluethroats breeding in their eastern range (Chukotka) to test whether they also use a route west of the Himalaya to the same wintering grounds as their European conspecifics, or shortcut east of the Himalaya. We retrieved one of the 30 bluethroats tagged which clearly showed that it migrated east of the Himalaya to a wintering area tentatively located in Myanmar. By assuming that this bird is representative for the migration of eastern Cyanecula s. svecia, we can reject our initial hypothesis of a common migration route of all Cyanecula s. svecia. The different routes and wintering areas of western and eastern Cyanecula s. svecia implicate the presence of a migratory divide somewhere north of the Himalaya, and further that the populations were in different refuge populations during the last glaciation.