Abstract
The foraging ecology of hoiho/yellow-eyed penguins (Megadyptes antipodes) breeding on Rakiura/Stewart Island has been investigated since the late 1980s, with research focusing on areas of high penguin prevalence. Across their mainland distribution (i.e. Te Waipounamu/South Island, Rakiura and its outliers) sites remain where few penguins breed, and little is known of their foraging ecology during breeding. This study examined locally adapted foraging behaviours at three previously studied colonies: Te Whaka ā Te Wera/Paterson Inlet, a large inlet on the east coast of the island, Whenua Hou/Codfish Island, a small predator-free island situated off the north-western coast of Rakiura, and Pikihatītī/Port Pegasus, a large harbour at the far south of Rakiura. During the 2020/21 season, nineteen adult breeding hoiho breeding from Pikihatītī, Te Whaka ā Te Wera, and Whenua Hou were fitted with time-depth recorder-GPS units to track their at-sea movements and diving behaviours. Additionally, eleven of these birds were fitted with video loggers to directly identify prey species upon capture and investigate differences in capture success rates, time investment, foraging effort, and diet composition between sites.
Penguins reached greater maximum depths, spent longer periods at the seafloor, and performed longer overall dives at Pikihatītī compared to birds foraging from Te Whaka ā Te Wera and Whenua Hou. Foraging radii and total trip lengths were smallest at Pikihatītī, where all birds foraged within a ~2sq km inshore area, travelling an average of 13.1 km per trip. At Whenua Hou, birds’ foraging trips were more widely dispersed, ranging >20km from shore, travelling on average 49.5 km across the gravels of Te Ara ā Kiwa/Foveaux Strait. Diet at both Pikihatītī and Whenua Hou was comprised mostly of opalfish (Hemerocoetes monopterygius), with minor contributions from squid (Notodarus sp.) at Pikihatītī, and blue cod (Parapercis colias) at Whenua Hou. Among penguins breeding at Te Whaka ā Te Wera only 5% of captures were successful, compared to 26% at Whenua Hou, and 53% at Pikihatītī. Foraging trips lengths at Te Whaka ā Te Wera averaged 19.16km, with mean foraging radii of 9.97km. The primary diet constituent at Te Whaka ā Te Wera was spotted wrasse (Notolabrus celidotus), a species never before recorded in hoiho diet. Diet diversity varied between sites. Diet from Te Whaka ā Te Wera was the most diverse, with five prey species identifiable from video data compared to only two species at Pikihatītī and Whenua Hou. Birds from Pikihatītī exhibited excellent foraging efficiency, with birds requiring on average 128s of cumulative dive time to capture one prey item, compared to 140s from Whenua Hou, and 760s from Te Whaka ā Te Wera.
Hoiho appear limited by the local bathymetry, prey distributions, prey densities, and environmental conditions directly adjacent to their colonies. Breeding hoiho showed rigid individual and intra-site consistency in the location of their foraging bouts over the period of sampling, with greater plasticity in benthic foraging behaviours appearing when inter-site behaviours are examined. The appearance of new species in hoiho diet, and identification of atypical foraging behaviours gives additional evidence for great behavioural plasticity in foraging hoiho within their mainland range.