Seasonal shifts in activity timing reduce heat loss of small mammals during winter

All activity imposes costs, but animals can often alter the timing of their activity to reduce these costs. Metabolic costs of activity are especially high during seasons of energy deficits (such as winter), but the extent to which animals can adjust their activity timing to reduce metabolic costs is unclear. Here, we test the hypothesis that the timing of small mammal activity during winter minimizes heat loss. Using motion-activated cameras deployed under snow, we show that a widely distributed nocturnal small mammal species (white-footed mouse, Peromyscus leucopus) shifted to diurnal activity in early winter, which reduced potential heat loss by 4%. The southern red-backed vole, Myodes gapperi, also avoided cold temperatures, but did so by adjusting its activity timing at a broader temporal scale by minimizing activity on cold days. We conclude that plasticity in activity timing – at both 24 h and multiday temporal scales – is an important means of conserving energy during winter and may need to be accounted for when forecasting species distributions, abundances and interactions.