Diving plasticity in the ancestral range of the yellow-eyed penguin Megadyptes antipodes, an endangered marine predator

Abstract

In long-lived marine predators such as penguins, foraging behaviour is related to breeding success. Yellow-eyed penguins Megadyptes antipodes are thought to be predominantly benthic foragers around mainland New Zealand, with previous dive studies showing little variation in diving behaviour and minimal change by year or breeding status. This apparent absence of foraging flexibility may be linked to local prey availability and therefore also to foraging success, factors believed to contribute to the current population decline. Here, we undertook the first detailed study of yellow-eyed penguin diving and foraging behaviour in the subantarctic Auckland Islands, part of the original ancestral range of the species that colonised mainland New Zealand. We collected dive logs from 134 foraging trips made by 73 breeders from Enderby Island, Auckland Islands, in the New Zealand subantarctic. Pelagic dives and foraging trips were recorded in the subantarctic population—a foraging strategy not previously published in dive studies on this species. Changes between benthic and pelagic foraging were recorded for individuals within foraging trips, within a breeding season, and between years. Differences in diving behaviour between the subantarctic and that reported for mainland New Zealand are likely influenced by local bathymetry and environmental conditions, and prey availability. However, the subantarctic population shows a greater use of pelagic foraging not evident in the northern population, even in areas that have a similar depth to some mainland foraging areas. This observed foraging flexibility may have implications for breeding success and potentially the long-term population trends of these 2 genetically similar populations.

Diet plasticity and links to changing foraging behaviour in the conservation of subantarctic yellow‐eyed penguins (Megadyptes antipodes)

“…The δ 13 C isotope levels were highest (less negative) in 2015, indicating that foraging was associated with more inshore and benthic habitats during this severe El Niño season. This is consistent with the higher proportion of benthic foraging trips evident in 2015 (Muller et al, 2020a). Carbon isotope levels were not affected by the maximum foraging distance away from the colony, or the cumulative foraging distance (length of trip).…”

“…Included in the feather samples were seven birds sampled in all three years, 14 birds sampled in two different years, and four birds sampled in a single year only. SIA data were matched with 22 dive logs, including 15 benthic and seven pelagic foraging trips (Muller et al, 2020a). A comparison (n = 9 pairs) was also made between blood and feathers representing the 2015 diet year (Figure S1).…”

“…Ground-based fieldwork was carried out on Enderby Island, Auckland Islands, in the New Zealand subantarctic (50 29 0 45 00 S 166 17 0 44 00 E, (Muller et al, 2021), and dive and breeding success data were collected in all three years (Muller et al, 2020a;Muller et al, 2020b). Nests were located using manual ground searching, ground-based very high frequency radio tracking, and aerial tracking using an unmanned aerial vehicle equipped with a very high frequency receiver (Muller et al, 2019).…”

Consistent Site-Specific Foraging Behaviours of Yellow-eyed Penguins/Hoiho Breeding on Stewart Island, New Zealand

“…A larger foraging range could indicate that sufficient prey is unavailable closer to breeding sites [ 10 , 11 ]. As central place foragers, seabirds must regularly return to incubate eggs or feed chicks for several months a year [ 12 ], although they are free to disperse over greater distances during the nonbreeding season [ 13 , 14 , 15 , 16 ]. Restrictions on areas available for foraging due to the necessity to return to their breeding colonies make seabirds particularly vulnerable to fisheries interaction in these areas and increase risk of mortality [ 17 ].…”

“…As yellow-eyed penguins are primarily benthic foragers within their mainland range [ 6 ], the maximum diving depth is determined by water depth and their physiological capacity to reach the seafloor [ 16 , 25 ]. Bottom time (the duration of a dive event spent actively foraging along the seafloor) can indicate the time required for a penguin to capture prey, or the time until it must return to the surface for air [ 26 ].…”