Evolution of foraging ecology in Fennoscandian tits (Parus spp.)

Species belonging to the same genus exploit similar resources in a similar manner. Despite their general similarities in behaviour, they differ in morphology, and these differences are often interpreted as adaptations for use of different resources. Here we report on the relation between morphology, habitat selection and feeding ecology in seven tit species (Parus spp.) in Fennoscandia. A problem previously disregarded in most ecomorphological studies is that members of a guild with closely related species share their common ancestry. This historical legacy causes similarity in ecology and morphology. We have used phylogenetic information with proper comparative methods to reveal the evolutionary associations. Our field data represented the winter, when tits commonly form mixed-species flocks and exploit non-renewable and limited food resources. Our rigorous analysis confirmed the previous suggestions that the smallest tit species tend to forage in the exterior tree parts whereas the heavier species use the inner parts. Another ecomorphological pattern is that tits inhabiting coniferous habitats have more slender bills than those inhabiting deciduous habitats. After removing the effects of historical legacy, we found strong support for adaptive interpretations of among-species variation in habitat selection and foraging site selection. Ecological variation along either of these two niche axes is associated with predictable morphological variation.