Multi-scale habitat requirements of forest bird species in a highly fragmented landscape

Land use changes in Europe have resulted in forest loss and fragmentation that have been proved to be key factors driving the decline of various forest bird populations. Quantifying the environmental factors which allow the persistence of forest birds in highly modified landscapes is therefore essential to enhance conservation efforts. In the present study, we defined the environmental factors determining the distribution of seven forest birds (Picus viridis, Dendrocopos major, Dryobates minor, Garrulus glandarius, Poecile palustris, Sitta europea, Aegithalos caudatus) in a central portion of the Po Plain, northern Italy. In the study area, less than 12% of the whole territory is covered by broad-leaved forests (concentrated along the main rivers) and tree plantations. To obtain a full picture of the habitat requirements of these seven forest bird species, we first conducted a survey of their populations using the point count method during the 2015 breeding season, following which, using resource selection functions, we investigated the effect of environmental variables on each species, mainly focusing on the role of natural forests and tree plantations. The effect of variables was assessed both at a home-range scale and at four different scales in the surrounding context. Tree plantations, in addition to natural forests, proved to be important for most of the seven species studied, including forest specialists such as Dryobates minor and Poecile palustris. The distribution of forest species was better explained by habitat amount than by habitat configuration, both at the home-range scale and in the surrounding context. As expected, Sitta europaea was the most sensitive species to land use changes, and broad-leaved natural forests were essential for its persistence in the landscape.