The work examined 177 bird species in the Alps, the Pyrenees, the mountains of Scandinavia and the British uplands. It used long-term monitoring data from the BTO/JNCC/RSPB Breeding Bird Survey alongside those from seven other European countries. 

Of the species considered, 63% had moved uphill, and by an average of about half a metre per year since the 2000s. The areas seeing the fastest change were in Scandinavia and the Alps. The Wheatear, for example, has shifted 33 meters uphill on average in the Scandinavian mountains since 2001. No significant uphill shift was observed in Great Britain or the Pyrenees, indicating that the causes of shifts, such as the intensity of climate change and human land use, vary from region to region. 

Mountain microclimates can vary considerably even over short distances. For example, the northern sides of mountains receive less sunlight than the southern sides, resulting in cooler and wetter conditions. These differences affect bird habitats, with sunny slopes attracting birds to higher elevations because vegetation zones and food resources are located higher up. However, birds are also moving uphill at the same rate on shady slopes, which suggests that warming temperatures are affecting the entire mountain landscape. The results show that broader climatic trends are driving birds to move uphill in the mountains across Europe. Slopes that are less exposed to solar radiation could serve as refuges, but these small-scale advantages are not enough to counteract large-scale uphill movements. 

Mountain areas are hotspots of biodiversity, home to many species that depend on specific climatic and habitat conditions. This information from this study is crucial for conservation planning in complex upland terrains.

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.