Abstract
Deciphering the effects of climatic conditions on population dynamics is of major importance in understanding how organisms are likely to be affected by climate changes. Using data from broad-scale annual censuses between 1990 and 2007, we show that winter and summer North Atlantic Oscillations affect several breeding success indicators of the Black Grouse () in the French Alps. We did not find any trend in hen counts or breeding indexes over the study period. Surprisingly for a bird specialised in cold climates, we show that Black Grouse optimise their reproductive output for positive values of the winter NAO corresponding to the average NAO index of the last 30 years. Extreme NAO values lead to lower breeding success, indicating that the grouse may be more able to track trends in climate than an increase in the frequency of extreme years. Our result show that, at least from a short-term perspective, Black Grouse productivity is not threatened by a trend towards warmer climatic conditions in the Alps, but may be affected by an increased frequency of extreme years. We advocate the use of the NAO as a climate proxy rather than using heavily noised and biased local climate descriptors in studies focusing on the global response to climate over a large spatial scale.