This work studied the effects of the environmental fluctuations on the demography of three species of marine birds breeding in sympatry on Adélie coast, Antarctic (southern fulmar, snow petrel and emperor penguin). One of the major results was the strong impact of sea ice on the demographic parameters and the population sizes of the three species. Moreover, analysis of the variability of the demographic parameters, population sizes and environmental variables suggested a regime shift in the Antarctic ecosystem at the end of the years 1970.
Adult survival was a key demographic parameter for the three species population dynamics, but breeding abstention also played an important role for snow petrel and southern fulmar population dynamics. Adult emperor penguins survival were strongly affected by environmental conditions, and particularly negatively influenced by low sea ice extent. On the other hand, none of the several environmental covariates had a significant impact on adult snow petrel survival. Southern fulmar adult survival varied little and was negatively influenced by warm events during winter. The proportion of birds attempting to breed was also negatively affected by a decrease of sea ice for the three species. Therefore, breeding population sizes of these three species were positively influenced by sea ice thought its effect on key demographic parameters. Indeed, environmental conditions, and especially sea ice, have both strong influence on key demographic parameters thought its impact on the food web processes, on the distribution and abundance of food supplies and on the nature and extent of breeding and feeding habitat.
We also showed that over the past 40 years, populations and demographic parameters of the three species fluctuated with a periodicity of three to five years that was also detected in sea-ice extent and the Southern Oscillation Index. Although the major periodicities of these interannual fluctuations are not common to different species and environmental variables, their cyclic characteristics revealed a significant change since 1980. Theses results suggested that a regime shift had probably occurred during this period, affecting significantly the Antarctic ecosystem, but with contrasted effects on the three species. Indeed, the dramatic 50% decrease in the emperor penguin population during the regime shift was probably related to warm anomalies, suggesting that this species may be very susceptible to environmental variability, and particularly to sudden changes in their environment. The mechanism was a high decrease in adult survival linked to warm events. Southern fulmars and snow petrels showed their lowest number in 1976, but they were able to skip reproduction, and seemed to be less sensitive to major changes in their environment.
Therefore, the population size of these three species will probably be negatively affected by reduced sea ice in the context of global warming. Moreover, emperor penguin populations were more susceptible to environmental variations than snow petrel and southern fulmar populations since petrels can avoid the important cost of reproduction by skipping a reproduction during unfavorable years. The emperor penguin population future will be uncertain in the context of climate change and other events such as the regime shift during the late 1970s.