Studying the effects of prey distribution on predator behaviour is complex in systems where there are multiple prey species. The role of prey density in predator behaviour is rarely studied in closed ecosystems of one predator species and one prey species, despite these being an ideal opportunity to test these hypotheses. In this study, we investigate the effect of prey density on the foraging behaviour of a predatory species in an isolated Antarctic ecosystem of effectively a single predatory species, and a single prey species. We use resource selection models to compare prey density in areas utilised by predators (obtained from fine-scale GPS telemetry data) to prey density at randomly generated points (pseudo-absences) throughout the available area. We demonstrate that prey density of breeding Antarctic petrels (Thalassoica antarctica) is negatively associated with the probability of habitat use in its only predator, the south polar skua (Catharacta maccormicki). Skuas are less likely to utilise habitats with higher petrel densities, reducing predation in these areas but these effects are present during chick rearing only, but not during incubation. We suggest that this might be caused by successful group defense strategies employed by petrel chicks, primarily spitting oil at predators.