Fig. 1
From: Gene expression in the brain of a migratory songbird during breeding and migration
Locations of willow warbler sampling sites in Sweden. The stippled lines refer to the approximate positions of the centres of two migratory divides around the Baltic sea, separating the ranges of SW migrating P. t. trochilus (light grey) and SE migrating P. t. acredula (dark grey). Breeding birds were captured at Stensoffa, Tångböle and Anjan, autumn birds at Stensoffa and Skeppshamn. The autumn capture site for P. t. acredula at Skeppshamn is south of the centre of the hybrid zone. At the date for capture at Skeppshamn (19 August), birds are expected to origin from further north in Scandinavia (well within the range of P. t. acredula) whereas locally hatched birds should already be further south on their move to the wintering grounds