High annual variability in reproductive success and survival of an Antarctic seabird, the snow petrel Pagodroma nivea : A 27-year study.

Demographic parameters were estimated for snow petrels Pagodroma nivea nesting at Pointe Géologie Archipelago, Adélie Land, Antarctica between 1963 and 1990; 21 years of data on adult survival and 27 years of data on breeding success are available. The average age of first return and first breeding were 8.1 and 9.9 years respectively and there was no signifcant difference between the sexes. The overall breeding success averaged 51.3% and was very variable between years (21-80%). Breeding failure was mostly due to incubation failure and annual breeding success was negatively correlated with average snow falls in October-November and October-March. Breeding frequency was very low, averaging 52% of seasons during a reproductive lifetime. Good quality sites, with high occupancy rate and high breeding success were few in the study plots. Poor years in 1966-1967, 1976-1977 and 1983-1984, with low breeding success, very low proportions of nets with breeding attempts and high numbers of non-breeders, occurred 1 year after large-scale El Niño Southern Oscillation (ENSO) events. Snow petrels exhibited very low philopatry. Only 45 birds have been recovered in the study plots from a total of 1115 banded fledglings giving an estimated rate of return of 12.9% between fledging and 3 years old. Annual survival between 3 and 10 years was 91.4%. Annual adult survival (93.4%), though variable, was low during poor years of 1977-1978 and 1983-1984. Adult survival of males (94.7%) was not significantly different from that of females (93.9%). Over the study period, the population of Pointe Géologie was stable. Using the estimated parameters, a Leslie model gave a growth rate of 0.948%, which was probably compensated by immigration (5.7% per year). Restricted numbers of good-quality sites at the place of birth could have led young birds to prospect other colonies and could have selected low philopatry. High adult survival, strong site tenacity and capacity to spread breeding over a long lifetime are probably part of the adaptive strategy of this small fulmarine petrel facing highly variable environmental conditions.