Associations between forest specialist birds and composition of woodland habitats in a highly modified landscape

Abstract

In Europe land use change has produced loss and fragmentation of the original forest habitat. On the other hand, the area covered by tree plantations and altered stands dominated by exotic tree species is increasing. Forest specialist birds are considered to be among the best candidates to assess the consequences of this transformation on wildlife. Here we investigate the link between the abundances of three forest specialist bird species (the Eurasian Nuthatch Sitta europaea, the Marsh Tit Poecile palustris and the Lesser Spotted Woodpecker Dryobates minor) and the woodland habitats of a highly modified landscape located in north-western Italy. In the area, the cover of anthropogenic woodland habitats, such as poplar plantations and Black Locust (Robinia pseudoacia) stands, exceeds that of native oak and riparian forests. During breeding season, birds were counted for three times along 105 transects of 300 m each, scattered in all the wooded contexts of the study area. Using n-mixture models, we investigated the effect of the amount and configuration of woodland habitats on the abundances of each species. First we selected for each variable the strongest scale of effect, ranging from 0.1 to 4 km. Then we built a full model including all variables at selected scales, accounting for correlation among variables and possible interactions. Forest specialists’ abundances were affected by the composition of the entire woodland mosaic, not of native forests only. A high cover of nonnative woodlands in the landscape showed a null or positive effect on the species, if combined with a high cover of native forests. However, at a local scale and when dominating in the landscape, nonnative woodlands had mostly a detrimental effect. Alongside with the protection of remnant native forests, it should be contemplated the retention of nonnative woodland habitats when these contribute to enhance the heterogeneity of the landscape.