Individual variation in energy-saving heterothermy affects survival and reproductive success

Given fundamental energetic trade-offs among growth, maintenance and reproduction, individual differences in energy saving should have consequences for survival and reproductive success. Many endotherms use periodic heterothermy to reduce energy and water requirements and individual variation in heterothermy should have fitness consequences. However, attempts to disentangle individual- and population-level variation in heterothermy are scarce. Here, we quantified patterns of heterothermy of 55 free-ranging eastern chipmunks (Tamias striatus), food-hoarding hibernators. Over five hibernation periods, we obtained a total of 7108 daily individual heterothermy indices (median: 118 per individual). Based on an individual reaction norm approach, we found that the use of heterothermy was repeatable and varied among individuals of the same population under similar environmental conditions. This among-individual variation had consequences for winter survival and reproductive success. Individua...