Forest bird populations in Europe have remained stable overall, unlike the drastic decline in the populations of farmland species. However, this apparent overall stability may hide large variation among species. We aimed to determine if forest bird species with varying life histories and biome distributions show different population trends. We used functional traits and specialisation indices to study changes in abundance and distribution of European forest bird populations, and to identify “winner”, “loser”, and stable species. We defined change in abundance as the population trend of each species over the last 40 years, and change in distribution as two components: range change (i.e., area shrinkage or expansion) and range shift (i.e., latitudinal adjustments), both over the last 30 years. We also considered specialist groups of different biomes (i.e., boreal, temperate, Mediterranean and biome generalists) separately. We show that while Mediterranean and temperate species have increased in abundance and range, probably as the result of warmer temperatures and forest expansion in these regions, boreal forest species have declined in abundance and range area. This probably results from changes in forest structure and composition due to forestry practices, increasing temperatures, and colonisation of warm-dwelling species. Among boreal species, the ones related to mixed forest (i.e., mix of broadleaf and coniferous trees) declined the most, both in abundance and range, and shifted northwards. In contrast, for vertebrate carnivores (i.e., birds of prey), we observed abundance increase among Mediterranean species and southward expansion among all species. We conclude that forest bird species in Europe are sensitive to the combined effects of land use and climate change, and these effects vary among the different biomes. Our results highlight the necessity of maintaining and restoring key forest habitats (e.g. through increased protected areas and extensive management) and halting or limiting climate change, especially regarding boreal species.

Studies have shown negative impacts of increased human pressures on biodiversity at local (alpha-diversity) and regional (gamma-diversity) scales. However, the diversity between local sites (beta-diversity) has received less attention. This is an important shortcoming since beta-diversity acts as a linkage between trends at the local and regional scales. Decreased beta-diversity means that local sites lose their distinctiveness, becoming more similar to each other. This process, known as biotic homogenization, is predicted to arise through the replacement of native specialists with native and non-native generalists. However, the mechanisms causing biotic homogenization have not been fully studied nor its impacts on different facets of biodiversity. We examined if land-use change due to human actions causes biotic homogenization of taxonomic, functional and phylogenetic diversity in bird communities of forested habitats in the state of Minnesota, USA. Our aim was to study if increased human pressure, which included human population density, land transformation, transport infrastructure, and electrical power infrastructure, was associated with increased similarity among bird point count sites. Our results showed that elevated human pressure was not related with increased biotic homogenization in this study region. Interestingly, increased human pressure appeared to increase the between-site functional diversity of bird communities. This association was driven by a decrease in local diversity, which, due to the nature of beta-diversity, led to an increase in between-site diversity. We highlight the importance of considering multiple facets of biodiversity and the use of beta-diversity in a conservation setting.