Can artificial habitat mitigate impacts of climate change? Quantifying nesting habitat microclimate and use by little penguins (Eudyptula minor)

• Main Author: Clitheroe, Erin
• Other Authors: Fontaine, Joe, Cannell, Belinda
• Format: Thesis
• Language: English
• Published: 2021
• Subjects: Penguin Island
• Online Access: https://researchrepository.murdoch.edu.au/id/eprint/59866/

Climate change continues to have significant effects on seabird species globally. Extensive work has linked variability in marine climate with changes in phenology, reproductive success and distribution for a wide range of taxa. Despite the reliance of seabirds on island and coastal habitats for breeding, comparatively few studies address the compounding effects terrestrial climate change may have on reproductive success and survival, particularly for populations breeding at the warm edges of a species’ range. Edge populations may be key for not only predicting species’ responses to expected change in climate but also for maintaining long term adaptive capacity of a species. For edge populations, conservation may rely on the intensive management and restoration of terrestrial habitat to facilitate population resilience and buffer the adverse effects of climate change. Among the critical elements of successful conservation planning for long term species persistence is a comprehensive understanding of habitat use, microhabitat conditions and climate change impacts at range edges. This thesis investigated the use and microclimate conditions of nesting habitat used by a disjunct rear edge population of little penguins (Eudyptula minor), seeking to identify implications of terrestrial climate change for this species. To achieve this, I characterised little penguin nesting habitat on Penguin Island, Western Australia and quantified relationships between nest attributes, microclimate (temperature and humidity), nest use and reproductive success. I monitored 50 natural nests and 113 existing nest boxes fortnightly for nesting activity and reproductive success over three little penguin breeding cycles (2013 - 2016). Nest characteristic data were collected, and microclimate measurements recorded using temperature and humidity loggers. Subsequently, I implemented a manipulative study testing artificial nest design and shading treatments to determine how to most effectively emulate the microclimate of natural cavities. Little penguins did not select nest sites randomly, but instead based nest site selection on topographical, vegetation and nest site attributes. Natural nests were preferentially selected at sites with taller vegetation, close to a known landfall site and with a south-westerly facing entrance. In contrast, nest box use was predominately driven by the structure of the box, with longer boxes more likely to be used. Neither landscape nor nest site attributes were found to influence the overall success of either natural or artificial nests. Nest boxes were ineffective at replicating microclimate conditions of natural nests. Nest boxes experienced consistently higher daily maximum temperature (~2 ˚C) and maintained temperatures above little penguins’ upper thermoneutral limits (30 ˚C and 35 ˚C) for around one hour longer than natural nests. After accounting for ambient temperature, relative humidity and wind, fine scale biotic and abiotic nest characteristics also influenced the maximum daily nest temperature and hours of exposure to upper thermoneutral limits (reducing time of exposure by up to two hours in natural nests and three hours in nest boxes). To further investigate the potential impact of climate change on temperatures within nests, I fitted models which simulated a 2 ˚C temperature increase scenario. The number of days annually where natural and artificial nest conditions exceeded thermally stressful conditions (≥30 ˚C) are predicted to increase by approximately 37% and 56% and the number of days exceeding hyperthermic conditions (≥ 35 ˚C) are predicted to increase by approximately 41% and 49% respectively. Such changes will expose penguins to dangerous and potentially fatal thermal conditions, particularly during the late breeding and moulting phases of their annual cycle. Experimental manipulation of boxes and shading revealed nest design and shading methods were effective at reducing nest temperature. Shaded timber boxes and buried plastic tunnels had thermal profiles either comparable to, or up to 2 ˚C cooler than, natural nests. Compared to exposed boxes, artificial shading and shading vegetation had the greatest buffering effect, significantly lowering maximum nest temperature by around 4.5 ˚C and reducing the time of exposure to upper thermoneutral limits by approximately one hour. Results here provide critical insight into how predicted changes in terrestrial climate may compound marine climate change impacts on seabird colonies at latitudinal margins, providing a more complete understanding of the climate limitations and management implications of edge populations. This thesis 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 could lead to the local extinction of this colony. I outline the potential to use well-designed artificial nests as a method for increasing the resilience of vulnerable populations. Crucially, this thesis reveals that management to ameliorate climate change impacts must be purposive and thoughtful and highlights the potential for poorly designed or positioned artificial nests to become not only ineffective but present an ecological trap, potentially accelerating population decline.