Abstract
Understanding habitat and resource use is fundamental to determining a species’ foraging ecology and guiding effective conservation strategies. Seabird foraging is shaped by a complex combination of breeding stage, intraspecific competition, and prey availability. As the marine environment is a highly dynamic system with spatial and temporal variability, prey is often patchily distributed. The kororā or little penguin (Eudyptula minor) is vulnerable to shifts in prey distribution caused by environmental change as global warming progresses, owing to their small size and inshore foraging behaviour. In recent years, climate impacts have become evident in the Pōhatu/Flea Bay colony (Horomaka/ Banks Peninsula, New Zealand). Monitoring of the colony has shown an increasing frequency of starvation events and an estimated population decline of approximately 375 breeding pairs since 2012/2013. The present research is the first to study the foraging ecology of Pōhatu Bay kororā, despite being one of New Zealand’s largest mainland colonies.
The first aim was to identify the marine distribution of Pōhatu kororā during the four breeding stages (prebreeding, incubation, guard, and postguard) using species distribution modelling and identify their key prey resources through stable isotope analysis. The findings will help to monitor the health of the Pōhatu Bay colony and inform conservation strategies in response to emerging threats, such as global warming. Using a dataset of 41 GPS foraging tracks collected during the 2023/2024 and 2024/2025 breeding seasons, the marine distribution of kororā was compared across breeding stages in relation to physical, climatic, and spatial environmental variables using Maxent species distribution models. The second aim was to determine if there were differences in prey trophic levels among breeding stages and foraging locations using isotopic analysis. Kororā guano samples were collected from tracked and untracked individuals across the 2023/2024 and 2024/2025 breeding seasons. By integrating spatial distribution and isotopic data, the present study highlights how prey availability shapes Pōhatu kororā marine distribution throughout the breeding period.
There was a clear pattern in the marine distribution of kororā between breeding stages, with individuals in prebreeding and incubation travelling long distances (> 100 km) into the Canterbury Bight, and individuals in guard and postguard (chick rearing) remaining within 30 km of the colony, which is indicative of central place foraging behaviour. These patterns aligned with environmental predictors in the models, with distance to the coast being the most influential during prebreeding and incubation, and distance to the colony during chick rearing. Isotopic analysis revealed higher and more consistent δ¹⁵N values among individuals foraging in the Canterbury Bight, which suggests kororā were targeting higher trophic level prey such as fish. In contrast, kororā during chick rearing stages had high individual variability in δ¹⁵N, as their foraging range becomes restricted around Banks Peninsula- causing individuals to target a broader range of prey. Minimal differences in δ¹³C values among breeding stages and between foraging locations likely reflect the inshore foraging behaviour of kororā and the similarity of coastal habitats.
Kororā exhibit behavioural plasticity in their ability to switch from long distance trips earlier in the breeding season, to shorter trips in later breeding stages. However, such flexibility may represent only a short-term adaptation as environmental change intensifies. If continued ocean warming drives prey distributions further from the colony, foraging areas may become inaccessible during the breeding season, ultimately reducing breeding success. Additionally, kororā foraged beyond marine protected areas around Banks Peninsula and in the Canterbury Bight, indicating that current protection measures may not encompass the full extent of their marine habitat, leaving kororā vulnerable to bycatch and resource competition with fisheries. The research presented here provides new insights to guide management decisions aimed at protecting critical habitats and prey resources for kororā, thereby supporting their population resilience under a changing climate.