Waterbird communities adjust to climate warming according to conservation policy and species protection status

Climate change is one of the strongest biodiversity threats. Worse still, the impact of multiple anthropic stressors on species dynamics could complicate adaptation to temperature increase. International conservation policies aim to protect ecosystems against anthropic pressures, but their ability to facilitate adaptation to climate change has yet to be assessed. Using wetland bird monitoring surveys, we evaluated the differences at the country scale of community adjustment to temperature increase of wintering waterbird communities (145 species) according to the implementation of the two main western Palearctic international conservation policies (Bern Convention and Birds Directive) in the Mediterranean basin (2786 sites, 22 countries) over a 22-year period. We showed that thermic community composition increases over time in countries which have enforced conservation policies. We found that strictly protected species under the Birds Directive and the Bern Convention contributed more to this community adjustment than the not strictly protected species. The mechanism results from a population increase in protected warm-dwelling species but not from a decline in cold-dwelling species. This study supports the ability of international conservation policies to mitigate the effect of climate change on animal communities.