Elevational shifts in bird communities reveal the limits of Alpine protected areas under climate change

Mountains are global biodiversity hotspots that are increasingly vulnerable to climate change. In the European Alps, rising temperatures and land-use changes have caused shifts in vegetation, impacting bird communities, particularly alpine specialists. Protected areas (PAs) are critical for buffering climate effects and safeguarding cold-adapted species, but their effectiveness in a warming world remains unclear. This study assessed shifts in bird assemblages across the elevational gradient in the Italian Alps over 13 years, using point counts to sample bird communities, and the Community Temperature Index (CTI) as a measure of community thermal tolerance. By comparing shifts inside and outside PAs, we identified key species and elevation bands driving CTI changes and modelled species-specific elevational shifts. Results revealed a critical divergence: CTI remained stable outside PAs, but increased sharply within PAs, reflecting a 1.19 °C rise in mean annual temperature in the study area. Initially, PAs harboured cold-adapted species, but over time, their bird assemblages became more similar to those outside PAs, likely driven by a decline in high-elevation species. The most marked changes occurred near the treeline, a key zone for sensitive species. CTI increases were driven by treeline and alpine grassland species which are most vulnerable to vegetation encroachment. Our findings suggest that PAs facilitate upward shifts, but are insufficient to prevent declines in populations of high-elevation species under rapid warming. Adaptive conservation strategies, such as targeted grazing, are urgently needed to counteract vegetation shifts, preserve habitat heterogeneity, and maintain elevational connectivity. Continuous monitoring is crucial to track ecological changes and refine conservation priorities, ensuring mountain biodiversity resilience under climate change. • Mountains host unique bird species but are highly vulnerable to climate change. • Community Temperature Index increased sharply within protected areas. • Protected areas showed limited buffering for cold-adapted bird species. • Treeline habitats are hotspots of change, driven by vegetation encroachment. • Conservation strategies must address habitat shifts to sustain alpine biodiversity.