The geographical range of British birds expands during 15 years of warming

<b>Capsule</b> Abundance monitoring data suggest that the short-term response of breeding birds to recent warming in Great Britain has been range expansion, caused by poleward shifts of leading range margins and no significant shifts of trailing range margins.<b>Aims</b> To quantify latitudinal and elevational shifts of breeding bird populations in Great Britain and test for differential shifts in range margins during a period of warming (1994–2009).<b>Methods</b> We modelled the population density of 80 species as a smooth function of latitude, longitude, elevation and year. Reference points on the distribution curve were used to describe latitudinal and elevational shifts.<b>Results</b> Across species, poleward shifts in the leading range margin were greater than in the range-centre. The trailing range margin was largely static, providing evidence for significant range expansion. The magnitude of latitudinal range shift lagged behind the equivalent shift in temperature, suggesting that species may be accumulating a climatic debt. There was no evidence for consistent elevational shifts.<b>Conclusion</b> Contrary to the generally expected long-term consequences of climate change of range contraction, we show that the short-term response to recent warming has been range expansion. This suggests the mechanisms of short-term and long-term consequences of climate change may differ.