Solar Radiation Affects Bird Distributions but Not Elevational Shifts in European Mountains

Aim: Climate change is driving species towards higher elevations. While local shifts in elevation are well documented, patterns across entire mountain regions are less understood. On a local scale, abiotic factors, such as topography and solar radiation relating to microclimate, affect species distributions and can thus influence the rate of elevational shifts on mountain slopes. The impact of abiotic factors on biodiversity is evident, but range shift studies have mostly focused on groups of species with low mobility, such as plants. Location: Across European mountain regions of the Alps, Pyrenees, Scandinavia and the United Kingdom. Time Period: 2001–2021. Major Taxa Studied: One hundred seventy-seven bird species. Methods: We adopted a cross-scale community approach using abundance data to quantify the impact of the amount of solar radiation (measured as potential incoming solar radiation) on the mean elevational distribution and rate of elevational shifts of bird species in four European mountain regions. We modelled the impact of the amount of solar radiation using generalised linear mixed models. Results: We found that bird species inhabit higher elevations in areas receiving more solar radiation. We also found that the mean elevations at which species occur moved uphill by 0.5 m/year between the periods 2001–2004 and 2018–2021 across Europe. However, this rate of elevational shifts was similar between areas receiving low, medium and high amounts of solar radiation. We observed variations in the rate of elevational shifts that were fastest in Scandinavia and the Alps, while no uphill shift was observed in the UK or the Pyrenees. Main Conclusions: Our findings underscore the significance of abiotic factors, including solar radiation and climate change, driving, directly or indirectly, birds' elevational distributions. They also unveil consistent patterns of uphill shifts across different solar radiation regimes at a continental scale.