Wintering bird communities are tracking climate change faster than breeding communities

Global climate change is driving species' distributions towards the poles and mountain tops during both non-breeding breeding seasons, leading to changes in composition of natural communities. However, degree season differences climate-driven community shifts has not been thoroughly investigated at large spatial scales. We compared rates winter (non-breeding season) summer (breeding) their relation temperature changes. Based on continental-scale data from Europe North America, we examined bird using index (CTI) approach with observed regional 1980–2016. CTI increased faster than summer. This seasonal discrepancy probably because individuals are less site-faithful winter, can more readily shift wintering sites response weather comparison season. Regional long-term were positively associated but pattern was only significant due high annual variability Annual seasons. Our results broadly consistent across continents, suggesting some restructuring European American avian Because changed much season, it important increase our knowledge about impacts less-studied