Ultimate and proximate factors affecting the breeding performance of a marine top-predator

Variability in ecosystems affects the life history of organisms. In marine ecosystems where interannual variability is high, relationships between fluctuations in oceanographic parameters and top-predator breeding performance are increasingly documented but it is less clear why such relationships exist. In this study, we examined the connections between marine environment fluctuations and breeding performance of a long-lived top-predator, the black-browed albatross Diomedea melanophris at Kerguelen, through study of resource acquisition and allocation processes. Our results show that this population used the same foraging zones and spent similar time foraging year after year, but adult body condition varied between years. Foraging trips are regulated mainly by changes in body condition. During years of low resource availability, birds return to their nest with lower body condition and adults in low body condition were more frequent and therefore were more likely to stop breeding. Poor breeding success was related to the presence of colder waters in the foraging zones of breeding albatrosses as measured by the positive correlation between sea surface temperatures and breeding success measured over 18 years. Lower breeding Success was mainly due to failure by inexperienced birds. The results of this study demonstrate how oceanographic conditions affect breeding performance through allocation processes. We compared these results to those at South Georgia where the breeding success is lower and more variable. This population relies mainly on krill, a resource that shows a very variable year-to-year availability compared to fish prey consumed by Kerguelen birds. This study shows that, in the same species, differences in resource variability and availability affect the demographic strategies probably through differences in allocation strategies.