Warming threatens habitat suitability and breeding occupancy of rear-edge alpine bird specialists

Abstract

Alpine ecosystems are particularly vulnerable to climate change. For widely distributed alpine specialists, rear-edge populations are disproportionately important; it is expected that climate change will reduce their occupancy ranges due to the loss of suitable habitats and connectivity among them. Using four alpine bird species inhabiting the southwestern Palearctic as models, we aim to study which and how environmental factors influence habitat suitability, identify mountain areas with suitable habitat, estimate the probabilities of hosting breeding populations for these areas, and predict how habitat suitability and breeding occupancy will change under future climate scenarios. We used a species distribution modeling approach to obtain habitat suitability maps for four biological seasons and assessed the importance and effects of climatic and landscape variables for the studied species. We also assessed the probability of occupancy of potential breeding patches using available systematic distribution data, and projected our habitat suitability and occupancy models to future climate conditions. Our results indicated that the habitat suitability of rear-edge alpine specialists was limited mainly by climatic factors, restricting their suitable areas to the highest mountains where cold climate persist. The actual occupancy of the potential breeding patches was determined by their size, landscape connectivity and habitat quality. For the period 2041–2060 we predicted a substantial reduction of suitable habitats that varied across seasons and species, and a breeding occupancy range loss that varied across mountain ranges and species. Thus, these alpine bird species, currently not considered as threatened, merit a review of their conservation status. Common distribution patterns and potentially similar responses to climatic change suggest that our findings might be applicable for other rear-edge alpine species. Our study identified specific mountain systems where research and conservation efforts should focus for the conservation of alpine biodiversity in the southwestern Palearctic.