Drivers of change in mountain and upland bird populations in Europe

Mountain ecosystems have special significance for biodiversity and are vulnerable to climate and other environmental changes. However, few assessments of drivers of change have been conducted in these areas in comparison to other more accessible biomes. In this study, we developed an objective and broad definition of a mountain bird, and systematically reviewed the existing literature for the 34 European mountain and upland species identified in order to quantify which drivers of environmental change have been most consistently associated with positive or negative demographic responses. Raptors and gamebirds were the most-studied species, whereas mountain specialists and arctic-alpine species were little studied. Using a standardized threat classification, the analyses reported significant negative impacts of hunting, collision with energy-generation infrastructures, predation by competitive species, human disturbance and poisoning. There were significant positive effects for management of non-target species, but less support for effects of drivers operating over longer timescales, such as climate and land-use changes. Analysis of trends in drivers found evidence of increasing temperatures and vegetation encroachment, whereas agricultural impacts decreased, which was largely related to abandonment of grazing. A lack of fine-grained studies investigating ecological mechanisms and population responses to widespread impacts were highlighted. We have found that some drivers are well studied, but we need to collect more detailed and longer-term data on species requirements and on the impacts that bird populations face to devise priorities for conservation action and research for mountain and upland birds.