Population ecology and foraging behaviour of yellow-eyed penguins in New Zealand’s subantarctic Auckland Islands : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Science and Ecology, Massey University, Manawatū, New Zealand

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Penguins and other seabirds rely on healthy, functioning marine systems, and are vulnerable to human-induced changes. Accurate long-term monitoring of a threatened species’ population size and trend is therefore important for conservation management. The endangered yellow-eyed penguin (Megadyptes antipodes) is found only in New Zealand waters, with separate northern (mainland New Zealand and offshore islands) and southern (subantarctic) breeding populations. The northern population is declining, believed to be due to threats at sea including direct mortality, as well as changes to food supply, and the effects of climate change. The southern population was previously estimated to comprise at least 60% of the species. Despite this, the subantarctic has been little studied, with one previous population estimate at the Auckland Islands in 1989, two at Campbell Island, and no recent data or measurement of population trends. To address this data gap, this research studied the population and foraging behaviour (diving, foraging location, and diet) of breeding yellow-eyed penguins on Enderby Island, Auckland Islands, from 2015–2017. The first step for this research was locating cryptic yellow-eyed penguin nests hidden in thick vegetation, as ground searches are inefficient, time-consuming, and potentially hazardous for researchers in subantarctic terrain. I utilised a drone fitted with a novel multi-frequency VHF receiver which located nests in only 3% of the time for traditional search methods, facilitating my other research. Next, I defined methods for surveying populations in the subantarctic, and estimated a mean of 577 breeding pairs at the Auckland Islands, although the population and number of breeders fluctuated annually, and may have declined since 1989. My foraging research showed that 62% of foraging trips, and over 86% of all southern yellow-eyed penguin dives were pelagic (mid-water), unlike the predominantly benthic (seabed) dives of the northern population. Maximum dive depth was 134 m for benthic dives, and 115 m for pelagic dives, which is deeper than many northern penguins dive. The proportion of pelagic dives increased during La Niña years, likely influenced by climate conditions and prey availability. Foraging distance also varied, with a maximum distance of 47 km from shore, further than many northern birds travel. Foraging area size was greater for females and for pelagic foragers, although benthic foragers travelled further from shore on average. Diet also varied, and during El Niño conditions comprised lower trophic level prey, which were more benthic, and found closer to shore than during La Niña years. Diet results showed some individuals maintained consistent foraging behaviour, although foraging plasticity was also evident. Some individuals changed their foraging behaviour between years, and even within a breeding season. Variable breeding success in the subantarctic, along with variable foraging behaviour and diet suggests that prey availability is likely limiting the southern population in some years. Prey availability is therefore expected to be a major influence on survival and breeding success in the future, particularly if the effects of climate change become more pronounced.
Yellow-eyed penguin, Ecology, Food, New Zealand, Auckland Islands