Foraging areas and plasticity of yellow-eyed penguins Megadyptes antipodes in their subantarctic range

Foraging behaviour is crucial to breeding success for marine predators, including seabirds. Yellow-eyed penguins Megadyptes antipodes are central-place, predominantly benthic foragers around mainland New Zealand. The northern (mainland) population of this Endangered species is declining, with changes in the marine environment a suspected cause, particularly warming water and poorer foraging success. We undertook a detailed foraging study of the datadeficient subantarctic population, which is distinct from the northern population. Over 2 breeding seasons, we collected 91 GPS foraging logs from 69 breeding yellow-eyed penguins from Enderby Island, Auckland Islands, New Zealand. The mean foraging distance was 24 km from shore (max 47 km). Foraging area size was greater for females and for pelagic foragers, although benthic foragers travelled further from shore on average. Diving plasticity was evident both in diving behaviour and foraging area use. Foraging area and distance from shore were greater for all birds in a year of greater breeding effort and fledging success (2016). Foraging occurred over continental shelf waters, similar to the mainland, and in areas up to 150 m deep, so any differences in foraging behaviour compared to those reported for the northern population are likely influenced by local bathymetry, environmental conditions, and individual preference. Despite comparable bathymetry in some areas, the southern population showed greater foraging plasticity, with 62 % of foraging trips categorised as pelagic, implying that subantarctic foraging conditions may differ from the predominantly benthic mainland foraging. Variable foraging conditions may therefore have implications for future breeding success in the subantarctic.