The origin of Blackcaps Sylvia atricapilla wintering on the British Isles

Abstract

A migration route leading central European breeder Blackcaps to their winter quarters in Britain and Ireland was discovered in the 1960s. This phenomenon, representing a rapid evolutionary change of migratory behavior, can be explained by a shift in migration course towards the west and north-west (as opposed to the standard south-west direction) or reverse migration. These hypotheses were evaluated by analyzing the recoveries of Blackcaps either ringed or recovered on the British Isles. Blackcaps arriving in the British Isles from Scandinavia had been ringed over two weeks later than had been birds arriving from Central Western Europe, while no significant difference was found in the recovery dates of birds from these regions. Moreover, birds ringed in Scandinavia were recovered significantly later on the British Isles than in the continental Europe. This finding suggests that two populations migrate through Scandinavia: the local breeding population (migrating towards the south) and another with an unknown origin (possibly Central European, heading towards the north and west). Thus, some of the Blackcaps ringed in Utsira on the Norwegian west coast, and ending up to the British Isles, might be of Central European origin.