MORPHOLOGICAL EVOLUTION AND CHANGES IN FORAGING BEHAVIOR OF ISLAND AND MAINLAND POPULATIONS OF BLUE TIT (PARUS-CAERULEUS) - A TEST OF CONVERGENCE AND ECOMORPHOLOGICAL HYPOTHESES

We study the leg morphology and feeding postures of two subspecies of the Blue Tit (Parus caeruleus; Tenerife island and the Iberian Peninsu la) and the Coal Tit (Parus ater; Iberian Peninsula). We search for ev idence supporting the hypothesis of convergent evolution in morphologi cal and ecological traits and we discuss the role of ecomorphological hypotheses as predictors of foraging differences at the intraspecific level. To overcome the problems introduced by environmental characteri stics not related to locomotion and competition, we make observations under controlled situations to manage food quality and food access. We determine that the island Blue Tit has a longer tarsometatarsus, larg er foot span and a more proximal insertion of the tibialis cranialis m uscle (flexor of the tarsometatarsus) than the mainland Blue Tit. Thes e morphological differences are consistent with the more frequent use of hanging and clinging 'head-up' postures by the Iberian Blue Tit. Se veral ecomorphological hypotheses obtained at the interspecific level with other taxa, have proved to be of high predictive value for explai ning ecological differences considering morphological evolution. The T enerife Blue Tit and the Iberian Coal Tit clearly show close convergen ce in both feeding postures and leg structure, although some differenc es in morphology were found between these two species. Convergence in foraging methods between the island Blue Tit and the mainland Coal Tit can be explained without considering current interspecific competitio n as a determinant of niche space.