Comparing patterns in abundance and diversity of hole-nesting birds in Mediterranean habitats.

Hole-nesting birds include species highly dependent on old trees or dead wood for nesting, roosting, breeding and feeding. In this study we characterize the assemblages of these species occurring in five different habitat types located in a heterogeneous Mediterranean landscape. We used the point count method. In all habitat types, tits (Parus major and Cyanistes caeruleus) were the most abundant species, except in beech forests, where Sitta europaea showed the highest mean abundance. Hole nesting bird assemblages increase in abundance, richness and diversity, with significant changes from termophilic and sclerophyllous forests (Holm-oak and Cork-oak) to temperate and mesophilic forests (chestnut, Turkey oak and Beech). This pattern reflects the progressive change in vegetation type both due to structure and species composition, ultimately due to progressive change in altitude and local climate. In particular, data at singles species level corroborate that the presence of mature and dead trees (i.e., with high mean diameter) may explain the abundance of Sitta europaea, Picus viridis and Certhia brachydactyla. Our dataset highlights that, for the hole-nesting birds, mesophilous beech and oak Mediterranean forests of biogeographic and conservation concern, represent suitable habitat types for these specialized species.