Little penguins select more isolated nest boxes for breeding, but lay date influences breeding success

Abstract

Little penguins (Eudyptula minor; known as kororā in te reo Māori, the Indigenous language of Aotearoa New Zealand) depend on terrestrial environments for nesting, breeding, and molting, spending approximately 20% of their lives on land. Therefore, little penguins may select breeding habitats that could improve breeding success or survival. However, selection and its consequences differ across colonies because of varying threats and habitat contexts, requiring examination at the colony scale. We investigated the habitat and nest box characteristics influencing little penguin breeding ecology during the 2022 and 2023 breeding seasons at the Pōhatu/Flea Bay colony on Banks Peninsula, New Zealand. Using weekly monitoring data from 194 nest boxes, we applied generalized linear models and occupancy models to assess how these characteristics influenced breeding nest box selection, hatching success, and fledging success. Additionally, we explored the influence of breeding timing and hard tick (Ixodes eudyptidis) abundance in the hatching and fledging success models. Little penguins selected more isolated nest boxes for breeding, with >75% breeding probability at nest boxes >2 m from a neighbor. Older nest boxes were selected slightly preferentially for breeding, potentially increasing little penguins' exposure to ticks as these boxes had higher tick presence. Breeding success was primarily influenced by the timing of egg laying, where hatching success declined with later lay dates in the 2022 and 2023 breeding seasons. Fledging success decreased by approximately 50% across the lay period in 2022 but remained high (>75%) across similar lay dates in 2023. Our results suggest that nest box characteristics may be related to little penguin breeding nest box selection, whereas hatching and fledging success may be more influenced by timing of breeding and factors not included in our models. We recommend that nest boxes be placed at least 2 m from neighboring boxes within the breeding colony and that older boxes should be preserved where possible. Integrating continued monitoring with wider ongoing conservation efforts in an adaptive management framework is crucial to refining nest box placement and enhancing breeding success.