Shaping the body mass distribution of Passeriformes: habitat use and body mass are evolutionarily and ecologically related

1. The effect of habitat structure on the distribution of the number of species by body size classes was analysed for 277 Passeriformes of the Western Palearctic. 2. The evolutionary history of the group accounted for 68 % of the interspecific variation in body mass (estimated with the phylogenetic autoregressive method). The phylogenetic effect decreased from the most recent taxonomic level towards the earlier phases of evolutionary history. In a more fine-grained study with a subset of 55 passerine species living in central Spain, phylogeny explained significant proportions of the interspecific variation in body mass (62%), habitat use (foraging on the ground vs. foraging in the foliage of scrub/trees; 27%) and structural complexity of preferred habitats (12% ). 3. Throughout the evolutionary history there has been a considerable concentration of species around a body mass of 10-40 g (increase in kurtosis). and species with greater body masses have also appeal-ed (increase in skewness). 4. When the effect of evolutionary history on present-day variation in body mass was removed (specific component of the phylogenetic autoregressive method), the distributions of body masses changed with the structural complexity of preferred, habitats: species from woodland habitats were lighter (mainly because of the large frequency of small-sized species) and their body masses were less concentrated around the modal class than in species from open-country habitats. Results for the phylogenetic component (attributable to the phylogenetic relatedness of the species) were similar to those of the specific component. 5. Habitat use (i.e. the use of foraging substrata) was strongly correlated with body mass in a subset of 55 species living in central Spain: species foraging on the ground were heavier than those foraging in foliage and small branches of scrub/trees. This result was significant with both specific and phylogenetic components. Habitat use and structural complexity of preferred habitats were significantly correlated using both the specific and the phylogenetic components: species that mainly forage on the ground are mainly open-country species, while species that forage in pliable and slender substrata have mainly woodland habitats. Structural complexity of preferred habitats was negatively related to body mass, although this correlation was only significant using phylogenetic residuals (specific component). 6. These results show that the evolutionary history of Western Palearctic Passeriformes has not produced neutral variation in body mass with respect to habitat preferences and habitat use.