Observed impacts of climate change on terrestrial birds in Europe: an overview

Climate change is predicted to be the major threat to biodiversity by 2100, when the global average temperature may increase by 5-6 degrees, according to current predictions and trends in greenhouse gas emissions. However, many impacts of climate change on biodiversity have already been observed. These observed effects provide tangible evidence to motivate action to mitigate against further climate change. Focusing on Europe, this overview summarises recently published observed impacts of modern climate change on birds. Due to the sensitivity of birds to weather fluctuations, the high numbers of ornithologists throughout Europe and the tradition in the long-term study of bird populations, there is no doubt that climate change impacts on birds have already occurred. These impacts include changes in (i) phenology (e.g., breeding times), (ii) migration patterns (e.g., time of spring arrival from the wintering grounds), (iii) species distribution (e.g., poleward shift of range margins) and (iv) abundances (e.g., population declines of habitat-specialist birds). Although the overall evidence available is comprehensive, there is a challenge in disentangling the effects of climate change from those of other concurrent factors such as habitat loss and degradation, e.g. due to large-scale intensification of agriculture. Birds are coping with climate change by means of their phenotypic plasticity, but little evidence is available to prove that evolutionary adaptation is already taking place. Further climate change is likely to affect birds at many levels, from changes in body size to shifts in assemblage composition, from mismatches with their resources to the introduction of exotic species and new diseases: the interactions among these levels need to be considered in future research and to devise effective conservation strategies. The rapid development of this key topic in conservation biology and applied ecology makes it important to ensure long-term funding for research, review and dissemination.