Divers of climate change impacts on bird communities

1. Climate change is reported to have caused widespread changes to species’ populations and ecological communities. Warming has been associated with declines in long-distance migrants, reductions in habitat specialists and increases in southerly distributed species. However, the specific climatic drivers behind these changes remain undescribed. 2. We analysed annual fluctuations in the abundance of 59 breeding bird species in England over 45 years to test the effect of monthly temperature and precipitation means upon population trends. 3. Strong positive correlations between population growth and both winter and breeding season temperature were identified for resident and short-distance migrants. Lagged correlations between population growth and both summer temperature and precipitation identified for the first time a widespread negative impact of hot, dry summer weather, whilst resident populations appeared to increase following wet autumns. Populations of long-distance migrants were negatively affected by May temperature, consistent with a potential negative effect of phenological mismatch upon breeding success. There was some evidence for non-linear relationships between monthly weather variables and population growth. 4. Habitat specialists and cold-associated species showed consistently more negative effects of higher temperatures than habitat generalists and southerly-distributed species associated with warm temperatures, suggesting that previously reported changes in community composition represent the accumulated effects of spring and summer warming. 5. Long-term population trends were more significantly correlated with species’ sensitivity to temperature than precipitation, suggesting that warming had had a greater impact on population trends than changes in precipitation. Months where there had been the greatest warming were the most influential drivers of long-term change. There was also evidence that species with the greatest sensitivity to extremes of precipitation have tended to decline. 5. Our results provide novel insights about the impact of climate change on bird communities. Significant lagged effects highlight the potential for altered species’ interactions to drive observed climate change impacts, although some community changes were driven by more immediate responses to warming. In England, resident and short-distance migrant populations have increased in response to climate change, but potentially at the expense of long-distance migrants, habitat-specialists and cold-associated species.