Abstract
Aim Population trends reflect influence of environmental drivers acting upon species' population dynamics. As the strength of this influence may change predictably in space, we test multiple hypotheses about spatial gradients in the effects of environmental drivers on bird population trends across the continent.
Location Europe. Methods We used country-level population trends for 249 bird species in 32 European countries.
For each species, we expressed values of 12 traits which mirror the influence of major environmental drivers: climate change, land-use change and change in environmental legislation. We related these traits to population trends using generalized additive mixed models and tested for the presence of spatial gradients by including the interaction of countries' geographic position with four of these traits for which we hypothesized spatial patterns in relationships to trends.
Results Species listed for the longest time under Annex I of the EU's Birds Directive had increasingly positive trends towards the north-west, but an indication of the opposite pattern was found for shorter-listed species. Cold-adapted species had increasingly negative trends towards the North and especially the north-west, whereas the trends of the warm-adapted species were generally positive and increased in northern direction.
Spatial gradients in trends were weaker for the habitat niche position with forest species having positive trends in North-Eastern Europe and open-habitat species having negative trends in the Westernmost edge of the continent. Main conclusions The influence of all major hypothesized drivers varies across Europe.
Climate change impacts are probably most detrimental in North-Western Europe for the Arctic and upland birds, whereas the warm-adapted species may benefit from these changes at the same time. The differences in the enforcement of environmental legislation among countries are a likely driver of the spatial patterns for the Annex I species, whereas the unification of land-use intensity may be the cause of relatively weak patterns in the habitat niche effects.