High-elevation habitats are important for birds during the post-breeding migration period in the Alps

Mountain habitats harbour significant breeding populations of alpine bird species, yet they can also be important from a biodiversity conservation point of view outside the breeding season. High-elevations are likely important fuelling habitats for birds during the post-breeding period due to seasonal peaks in arthropod abundance being later relative to lowlands. There is no detailed study of bird communities using high-elevations in the post-breeding migration period in Europe. In this study, we recorded birds on line transects from August to October in 2021 and 2022 across an elevational gradient in the Western Italian Alps to assess how the abundance and diversity of birds varied in time and space during the autumn migration period. We detected 104 species in total, representing 22% of the Italian list of terrestrial bird species, showing that a wide range of bird species exploit these habitats. The highest bird diversity and abundance were found during the early migration period at the end of August when long-distance migrants use high elevations. Treeline habitats and south-facing slopes held the highest abundance of migrants, probably due to the high structural diversity and relatively high solar radiation which might affect thermoregulation and prey activity. We suggest that future management of protected areas in the mountains should take these parameters into account in order to protect mountain bird diversity, not only during the breeding season, but also in other key periods of the annual cycle, such as post-breeding migration. It is also essential to counteract the effects of climate and land-use change in mountain habitats by promoting conservation strategies for Alpine biodiversity, including migrants, over the entire year.