By contrast with diurnally active mammals that might need to increase evaporative water loss to keep cool, mammals active during the night might need to increase their metabolic rates to keep warm, which may impose an extra demand for energy during cold nights. Nocturnal species already are active at the cooler time of day, so one might predict less change in their activity patterns in response to increasing heat and aridity. If cooler microclimates are not available or if reduced diurnal activity compromises energy intake, diurnal species may increase their nocturnal activity ( Hetem et al., 2012a Levy et al., 2019). Those adjustments reduce the demand for water for evaporative cooling. Many mammals buffer the effects of increasing heat and aridity, occurring with climate change, by seeking cooler microclimates and reducing diurnal activity ( Hetem et al., 2012a McFarland et al., 2014). Understanding flexibility in activity patterns of mammals is crucial for predicting their resilience to climate change ( McCain and King, 2014). Large mammals that reproduce slowly and are unable to move to more suitable surroundings require flexibility in behaviour and physiology to survive in rapidly changing environments ( Fuller et al., 2016). Our results do not bode well for aardvarks facing climate change, and for the many animal species dependent on aardvark burrows for refuge. Seven study aardvarks and several others died, presumably from starvation. Despite their physiological and behavioural flexibility, aardvarks were unable to compensate for reduced food availability. Aardvarks also shortened their active periods by 25% during food scarcity, likely to avoid energetic costs incurred by foraging. When body temperatures were low, aardvarks often emerged from burrows during daytime, and occasionally returned before sunset, resulting in completely diurnal activity. Throughout the subsequent winter, the aardvarks’ minimum 24-h body temperatures declined, causing exaggerated heterothermy (4.7 ± 1.3☌ absolute range 24.7 to 38.8☌), with one individual’s body temperature varying by 11.7☌ within 8 h. During a summer drought, aardvarks relaxed the precision of body temperature regulation (mean 24-h amplitude 2.3 ± 0.4☌) and those that subsequently died shifted their activity to progressively earlier times of day in the weeks before their deaths. Under non-drought conditions, aardvarks tightly controlled their 24-h body temperature rhythm (mean amplitude of the 24-h body temperature rhythm was 1.8 ± 0.3☌ during summer and 2.1 ± 0.1☌ during winter) and usually were nocturnal. To measure their thermoregulatory patterns and foraging activity, we implanted abdominal temperature and activity data loggers into 12 adult aardvarks and observed them for varying durations over 3 years in the Kalahari. We hypothesised that the minimum 24-h body temperature of aardvarks would decline during energy scarcity, and that aardvarks would extend their active phases to compensate for reduced resource availability, possibly resulting in increased diurnal activity when aardvarks were energetically compromised. Aardvarks ( Orycteropus afer) are nocturnal, obligate ant- and termite-eating mammals which may be threatened directly by increasing heat and aridity, or indirectly by the effects of climate change on their prey. Conversely, when resources are limited, some nocturnal species become more diurnal, reducing energetic costs of keeping warm at night. Shifting activity to cooler times of day buffers animals from increased heat and aridity under climate change. 6School of Animal, Plant and Environmental Sciences, Faculty of Science, University of the Witwatersrand, Johannesburg, South Africa.5Laboratoire de Biométrie et Biologie Evolutive, UMR 5558, Université de Lyon, Université Lyon 1, CNRS, Villeurbanne, France.4Department of Biological Sciences, Faculty of Science, University of Cape Town, Cape Town, South Africa.3Research Institute of Wildlife Ecology, Department of Integrative Biology and Evolution, University of Veterinary Medicine Vienna, Vienna, Austria.2Centre for Veterinary Wildlife Studies and Department of Paraclinical Sciences, Faculty of Veterinary Science, University of Pretoria, Pretoria, South Africa.1Brain Function Research Group, School of Physiology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa.Nora Marie Weyer 1*, Andrea Fuller 1,2, Anna Jean Haw 1,3, Leith Carl Rodney Meyer 1,2, Duncan Mitchell 1, Mike Picker 4, Benjamin Rey 1,5 and Robyn Sheila Hetem 1,6
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