Adélie penguin response parameters signal reduced prey accessibility: implications for predator–prey response curves

Abstract

Seabirds are often proposed as useful indicators of marine ecosystems because of their typically tight response to varying levels of prey abundance. We demonstrate here how this relationship can be modified for Southern Ocean higher-order predators when prey accessibility changes as a consequence of the temporally varying sea-ice environment. We examined within- and between-year fluctuations in breeding success, foraging trip duration, meal mass and fledgling weights of Adelie penguins (Pygoscelis adeliae) at Bechervaise Island (67°35′S, 62°49′E) in east Antarctica to determine the degree of concordance between parameters over a 12-year period and how these varied in relation to sea-ice conditions. The penguins responded to extensive sea-ice (predominantly fast-ice) adjacent to their breeding colony by lengthening their foraging trips, and these years typically had reduced breeding success. Some years indicated good conditions for the penguins across parameters and had relatively high breeding success with heavier fledglings, while others indicated difficult conditions with poorer breeding success and lighter fledglings. In other years, there was discordance in the patterns of breeding success, fledgling mass and early versus late stage foraging trip durations, suggestive of different thresholds for different parameters or within-year changes in resource availability. Our results highlight the importance of accounting for the temporal variability in prey availability as a function of both accessibility and abundance when interpreting predator response curves.