Temperatures inside little penguin Eudyptula minor artificial nest habitats exceed upper thermal limits in a range edge population

Abstract

Rising global temperatures will have profound impacts on species and ecosystem functioning. Species existing near their thermal thresholds will be particularly vulnerable to these changes, and those species that rely on, or preferentially use, artificial structures may face pronounced effects. Gaining insights into the anticipated climate changes, both present and future, is crucial for informing conservation practices and the utilisation of artificial structures in conservation efforts. Using three years of data, we quantified and compared temperature of artificial nest boxes installed between 1986 and 2006 and natural nest burrows of a fringing population of little penguins existing at the northwestern limit of their range. Nest boxes were ineffective at replicating conditions of natural nests, exhibiting consistently higher daily maximum temperature (~ 2˚C) and exceeded upper thermoneutral limits for longer than natural nests. Fine scale biotic and abiotic nest characteristics influenced maximum nest temperature and time exposed to temperatures ≥ 35˚C. Simulated temperature increase of 2˚C predicted an increase in the number of days exceeding thermally stressful conditions (≥ 35°C) by up to 49%. Such increases will expose penguins to potentially fatal thermal conditions, particularly during the late breeding and moulting phases of their annual cycle. This study revealed that current and future thermal environments of little penguin terrestrial habitat on Penguin Island can exceed physiological limits for this species. Intervention to improve artificial nests and better quantify consequences is urgently needed given recent estimates of a declining population and increasing risk of local extinction.