We examined the within- and between- year fluctuations of four Adélie penguin population parameters which are thought to be sensitive to changes in prey availability: breeding success, foraging trip duration, meal mass and fledgling weights. Some years had either good breeding success with heavy fledglings or poor breeding success with light fledglings while others had a lack of concordance between breeding success and fledgling weight. These discordant years also had an inconsistency between the duration of early and late stage foraging trips. For example, low breeding success was recorded in a season with long foraging trips during the guard period, relatively short trips during the crèche period and heavy fledglings. These results may indicate changes in the relative level of resource availability between the guard and crèche stages of the breeding season (i.e. was relatively low during the guard stage and elevated during the crèche stage). The overall temporal variability across years in response parameters was much greater than was observed in the two years with concurrent krill abundance. If the temporal variability in predator response parameters at this site is largely driven by changes in prey availability then these results would add further weight to significant changes in predator response only occurring with changes in krill availability at low levels (ie the Hollings type II shape curve). Our results highlight the importance of taking into account the changing behaviours of birds in the context of life history requirements, changes in prey accessibility as well as any temporal variability in the amount of prey present when interpreting predator response parameters.
Sarah Mackey (CCAMLR Secretariat)