Browsing by Author "French RK"

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    Diet plasticity and links to changing foraging behaviour in the conservation of subantarctic yellow-eyed penguins (Megadyptes antipodes)
    (John Wiley and Sons, Ltd, 2022-05-17) Muller CG; Chilvers BL; French RK; Battley PF
    1. Diet is a key factor affecting seabird foraging behaviour, ultimately influencing survival, breeding success and long-term population viability. The density and distribution of prey species in the marine environment are influenced by many factors including climate effects such as El Niño southern oscillation and climate change that alter water temperature. 2. While poor quality diet has been implicated as a contributing factor in the decline of some mainland New Zealand yellow-eyed penguin (Megadyptes antipodes) populations, little is known about their diet in the subantarctic where the majority of the species breeds. 3. Blood and feather samples (n = 63) were collected for stable isotope analysis of diet from 25 individual birds breeding on subantarctic Enderby Island, Auckland Islands, New Zealand, from 2015 to 2018. 4. Diet data were analysed by factors such as breeding year, sex and foraging behaviour. Stable isotope analysis demonstrated significant changes in diet during each year of the study, which included both El Niño and La Niña conditions. 5. Diet during El Niño conditions comprised lower trophic level prey, which were more benthic, and found closer to shore than diet during La Niña. 6. Coupled with the reported variable breeding success of yellow-eyed penguins in the subantarctic, variable diet suggests prey availability is likely to be a limiting factor in some years. Prey availability is therefore expected to be a major influence on survival and breeding success of this endangered species in the future, particularly if the effects of climate change become more pronounced. 7. This research highlights an urgent conservation need to identify prey species utilized by the southern population, along with their distribution in time and space, and therefore also the effect of diet on long-term population stability.
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    Variable breeding success and its implication in the conservation of endangered yellow-eyed penguin (Megadyptes antipodes) at the New Zealand subantarctic Auckland Islands
    (John Wiley and Sons, Inc., 2024-04-19) Muller CG; Chilvers BL; French RK; Battley PF
    Knowledge of breeding success is essential for conservation, as it is required for monitoring populations and survival trends. Seabird reproductive success can be negatively affected by prey availability, marine-based stochasticity, extreme weather events, individual breeders' performance and direct threats such as disease, predation and fisheries interactions. The endangered yellow-eyed penguin (Megadyptes antipodes) is declining in mainland New Zealand, however, little is known about its breeding success in the subantarctic where the majority of the species breeds. Yellow-eyed penguin breeding success data were collected from a total of 167 nests on subantarctic Enderby Island, Auckland Islands, New Zealand, from the 2015 to 2017 breeding seasons. This included egg and chick mortality and fledging rates, plus a wider sample of the fledgling condition of 276 chicks. Fledging success was higher than in mainland New Zealand in some years, although chicks were smaller and lighter on average, highlighting the need for more information on juvenile survival probabilities in the subantarctic. Breeding success measures were similar in 2015 and 2016, but a large egg mortality in 2017 caused a significant reduction in breeding success that year. Such variability requires more investigation into the correlates of breeding success, including possible stressors such as foraging success, adverse weather and environmental effects, and pathogens. These results demonstrate the need for ongoing monitoring of yellow-eyed penguin breeding success across the subantarctic in order to establish baselines for normal variation and to determine whether anthropogenic (manageable) factors may be contributing to low productivity. This research highlights an important consideration for endangered species conservation; that breeding success may not be consistent over time, or across a species' entire range. Additional monitoring of all breeding populations should be carried out to ensure up-to-date information is available to inform conservation management decisions for the species.