Animal Energy Expenditures -- a Matter of Timing

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The expenditure of energy has been used as a currency for evaluating the performance and success of animals in free-living populations, just as it has also been used in descriptive and experimental laboratory studies of metabolism. Daily and seasonal rhythmicity of energy expenditure is a key element in the natural history and behavior of animal populations and represents the axis of adjustment to daily and seasonal changes in environmental conditions. I will review exemplary research that demonstrates the economy of behavioral and physiological adjustment to daily and seasonal patterns of environmental fluctuation. I will also attempt to highlight the differences between routine cycles of behavior supported by endogenous or environmentally triggered physiological functions and the retention of flexibility to deal with unpredictable conditions.

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