1. Centre d'Études Biologiques de Chizé, Centre National de la Recherche Scientifique, 79360 Villiers en Bois, France
2. Present address: Tour du Valat, Le Sambuc, 13200 Arles, France.

Correspondence to: Christophe Barbraud¹ Correspondence and requests for materials should be addressed to C.B. (e-mail: Email: barbraud@tour-du-valat.com).

Abstract

Variations in ocean–atmosphere coupling over time in the Southern Ocean^{1, 2, 3} have dominant effects on sea-ice extent and ecosystem structure^{4, 5, 6}, but the ultimate consequences of such environmental changes for large marine predators cannot be accurately predicted because of the absence of long-term data series on key demographic parameters^{7, 8}. Here, we use the longest time series available on demographic parameters of an Antarctic large predator breeding on fast ice^{9, 10} and relying on food resources from the Southern Ocean¹¹. We show that over the past 50 years, the population of emperor penguins (Aptenodytes forsteri) in Terre Adélie has declined by 50% because of a decrease in adult survival during the late 1970s. At this time there was a prolonged abnormally warm period with reduced sea-ice extent. Mortality rates increased when warm sea-surface temperatures occurred in the foraging area and when annual sea-ice extent was reduced, and were higher for males than for females. In contrast with survival, emperor penguins hatched fewer eggs when winter sea-ice was extended. These results indicate strong and contrasting effects of large-scale oceanographic processes and sea-ice extent on the demography of emperor penguins, and their potential high susceptibility to climate change.