Résumé
In the last decades, the effects of climate warming have been particularly marked in high mountain areas. High-altitude species adapted to cold temperatures are consensually held to be particularly vulnerable to climate warming. Among these species at risk, alpine birds like the Rock Ptarmigan (Lagopus muta) are expected to exhibit a strong negative response, particularly at the southern margins of their ranges in the northern hemisphere. In this study, conducted from 1998 to 2011, we investigated whether variations in the local climate affected the breeding biology of Rock Ptarmigan in the French Alps and Pyrenees. The median hatching date did not significantly advance in either massif, suggesting that Rock Ptarmigan did not breed earlier during this period. The date of snowmelt and spring temperatures influenced the onset of breeding but not consistently in both sites. In the Alps, the median hatching date was significantly correlated with the date of snowmelt, but this correlation was less clear in the Pyrenees. Unlike woodland grouse which inhabit lower elevations, the onset of breeding in Rock Ptarmigan may be related to both date of snowmelt and spring temperatures. Reproductive success varied greatly over the years and among sites. On average, the number of young per adult in the Pyrenean population was greater than that recorded in the two populations in the Alps. A significant positive trend of reproductive success over the period of 2000-2009 was detected in the Pyrenees but not in the Alps. The model that best explained annual variation in reproductive success included the additive effects of site, date of total snowmelt and rainfall after hatching. The estimates from this model showed that for all sites, reproductive success was much lower when snowmelt was late, and rainfall after hatching was high. We did not detect any altitudinal changes in locations of either breeding females or nests, suggesting that the breeding habitat of the species has not shifted upward from 1998 to 2011. To conclude, although the Rock Ptarmigan is generally considered a potential sentinel species for indicating temperature-induced changes in alpine avifauna, our study did not show a short-term effect of climate change on the breeding biology of the southern populations of this species.