Ecological and physiological convergence in thermoregualtion by Caprimulgid birds and Vespertilionid bats

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Energy is the currency by which the costs and benefits of many biological functions are measured and likely best explains behaviour by animals in general and endotherms in particular. My research program is focused on determining the ecological context for how, when and why endotherms use “heterothermy” to save energy. Daily torpor stems from reduced metabolism and thus reduced body temperature (Tb) leading to energetic savings. Its importance is underscored by the rapidly increasing number of species recorded to use it and the idea that it makes endotherms less susceptible to extinction.*******We study the use of daily torpor by both insectivorous bats and nocturnal birds (nightjars) whose responses converge ecologically and physiologically. In the short-term we will identify broad patterns in torpor use with a long-term goal of addressing why individuals employ it when they do, the cues used to initiate the response, and finally the reasons for the apparent flexibility of its use. Behavioural and ecological factors that likely influence torpor use include: body condition, social interactions, foraging success and roost structure. The relative importance of these factors is poorly understood and our research will assess the nature of interactions between them.*******We will measure torpor use by bats and birds in natural situations as part of a long-term study of big brown bats and following from recent work on silver-haired bats, both projects taking place in Cypress Hills, Saskatchewan and short-term studies of a variety of species including Common Poorwills, Whip-poor-wills in South Dakota, Common Pauraques in Panama, and Freckled and Rufous-cheeked Nightjars in southern Africa. For most projects, temperature sensitive radio-transmitters or data loggers will be used to collect data on body temperature as a proxy for metabolism to infer how free living animals use torpor. Where feasible we will use heart-rate telemetry to more directly assess the metabolism of free ranging animals. Where possible, we will experimentally manipulate food availability and or the energetic costs incurred by study animals to assess which factors are most important for stimulating torpor use.*******The most important outcome of my research program will be to refine a Heterothermy Framework relating the ecological determinants of torpor use by diverse animals. Overall our results will allow us to assess both the direct and interactive effects of variables such as resource availability, ambient temperature, roost structure, and social dominance on the degree of energy savings which accrue from heterothermy hopefully to be able to predict both species and circumstances when torpor will be employed by currently unstudied species. This will enhance our understanding of energy as an evolutionary currency.***