Population structure and migratory directions of Scandinavian bluethroats Luscinia svecica– a molecular, morphological and stable isotope analysis

Abstract

Many species of birds show evidence of secondary contact zones and subspeciation in their Scandinavian distribution range, presumably resulting from different post‐glacial recolonization routes. We investigated whether this is the case also in the Scandinavian bluethroat Luscinia svecica, a species that has been suggested to consist of two separate populations: one SW‐migrating and long‐winged (L. s. gaetkei) breeding in southern Norway, and one shorter‐winged ESE‐migrating (L. s. svecica) in northern Scandinavia. We sampled males at eleven breeding sites from southern Norway to northernmost Sweden. There were no morphological differences or latitudinal trends within the sample, neither were there any genetic differences or latitudinal trends as measured by variation in AFLP and microsatellite markers. Stable isotope ratios of throat feathers moulted on the wintering grounds showed no, or possibly marginal differences between birds from southern Norway and northern Sweden. We also re‐measured old museum skins that in previous studies were classified as L. s.gaetkei, and found marginally longer wings in birds from the southern part of the Scandinavian breeding range. The difference, however, was much smaller than proposed in earlier studies. We conclude that there is no evidence of a genetic population structure among Scandinavian bluethroats that would suggest the presence of a zone of secondary contact. Finally we discuss whether the presumed subspecies gaetkei ever existed.