Morphological variation in sympatric and allopatric populations of European Willow Warblers and Chiffchaffs

Abstract

The geographical variation of Willow Warbler Phylloscopus trochilus and Chiffchaff Ph. collybita males was studied in Finland (sympatry, but separated by breeding habitat), SWGermany (sympatry, in the same habitats) and Hungary (Chiffchaff only). The 32 external characters measured were treated as three functional complexes, the flight apparatus, foot and feeding apparatus. In the Willow Warbler, there was little geographical variation although the German birds differed from the three Finnish populations in the size of the flight apparatus and the shape of the feeding apparatus, and there were also significant differences among the Finnish populations. In the Chiffchaff, the differences between the Finnish, German and Hungarian populations were clear, the Hungarian population being intermediate between the other two. The less marked geographical differences in the Willow Warbler morphology are assumed to be connected with the similarity of its habitats and migratory habits in Finland and Germany. Finnish Chiffchaffs, breeding in spruce forest, did not seem to have special morphological adaptations to this habitat. The morphological difference between the Willow Warbler and Chiffchaff was greater in Germany than in Finland. The geographical variation of the Willow Warbler is so slight that the appropriateness of the currently recognised subspecies may be questioned . In the Chiffchaff the variation is more extensive and recognition of subspecies has more justification.