Nest microclimate and heat stress in African Penguins Spheniscus demersus breeding on Bird Island, South Africa

Abstract

Summary Low-latitude penguins naturally breed in burrows dug in guano. This affords them a buffered environment that remains cool and humid, reducing the risk of hyperthermia while on land. As a conservation strategy, several versions of artificial housing units have been trialled at various breeding sites of African Penguins (Spheniscus demersus) around South Africa, where former guano exploitation forced many penguins to breed in exposed surface nests. While some units yielded a positive effect on breeding success by providing protection against predation, none of them have effectively mitigated the risk of heat stress in penguins or their eggs. Here, we investigated the microclimate of a recent double-layered design of ceramic artificial nests and compared that to natural burrows, exposed surface nests, and commonly used cement pipe nests, in austral summer 2021 on Bird Island, South Africa. We also recorded penguin behaviour during the hottest period at each of these nest types using remote camera traps to determine the onset of heat stress (panting). Double-layered ceramic nests out-performed all other nest types, including natural burrows, by remaining cooler throughout the day, with temperatures never exceeding 36.7°C. By contrast, all other nest types had multiple episodes where temperatures exceeded 40°C. Double-layered ceramic nests also maintained constant levels of high humidity (relative humidity [RH] >70%) throughout our study, whereas low humidity levels were observed in surface nests (RH ≈ 60%) and cement nests (RH <50%) during midday heat. We observed penguins panting at temperatures of 25°C in nest boxes, and at 22°C in exposed surface nests. This suggests that heat stress in African Penguins may occur much sooner than anticipated and that they are particularly vulnerable to hyperthermia as climate change-related global warming progresses. Fortunately, we are encouraged by the capacity of double-layered ceramic nest boxes to buffer environmental extremes and maintain suitable breeding conditions.

Thermoregulatory strategies of songbird nestlings reveal limited capacity for cooling and high risk of dehydration

“…Our results show that when predicting how populations will change with climate, one cannot assume that the thermoregulatory strategies and thermal tolerances of adults can be extended to their nestlings. Additionally, weather conditions, such as humidity, rainfall, wind and solar radiation, and characteristics of the nest (Ricklefs & Hainsworth 1969;Ardia 2013;Welman & Pichegru 2022) as well as brood size, nestling behaviour (huddling or spreading further apart in the nest), and age of the nestlings (Mertens 1977;Andreasson et al 2016;Mitchell et al 2022) can affect their heat load and cooling requirements (Wolf & Walsberg 1996). These conditions can exacerbate ambient conditions, with nestlings incurring additional water loss or energy use maintain body temperature, or help mitigate the thermal environment, reducing water loss and energy requirements.…”

Effectiveness of novel artificial seabird nest modules for reducing ambient temperature transfer in a warming climate

“…The performance of shaded wooden boxes declined at the Carpentry Shop area during extreme heat events, a location that is more arid in nature with a southern aspect that receives higher solar input throughout the day than other portions of the island. Double‐layered ceramic nesting modules deployed at a colony of African penguins ( Spheniscus demersus ) in South Africa maintained higher levels of relative humidity compared to other habitat types (Welman and Pichegru 2022). Although not measured in our study, ceramic modules may have retained higher humidity levels compared to wooden boxes as well, explaining the ability to buffer against extreme heat even at the relatively drier sites on the island.…”

Microclimate, an important part of ecology and biogeography

“…Maintaining and creating microclimate heterogeneity and habitat connectivity is an effective basis for future‐proofing ecosystems which increases resilience to climate change (Hylander et al., 2022; Maclean & Early, 2023; Stark et al., 2023). Moreover, knowledge and data on microclimate heterogeneity can help identify organisms and ecosystems most vulnerable to climate change (McCullough et al., 2016), and when combined with biophysical ecology, this knowledge can improve and create new management practices to promote biodiversity (Briscoe et al., 2022; Ononye et al., 2023; Welman & Pichegru, 2023).…”