Social thermoregulation in Mediterranean greater white-toothed shrews (Crocidura russula)

Social thermoregulation is the huddling of two or more individuals that share endogenous warmth to reduce thermoregulation costs. Strategies vary widely depending on the species’ social behavior and the ambient ecological conditions. In greater white-toothed shrews (Crocidura russula), huddling is employed in communal nests only in the colder months, which suggests that temperature is an important factor in the species’ social thermoregulation strategy. To test this hypothesis, we analyzed the behavior and physiology of five groups of shrews from winter, acclimated to 14 °C, and four groups from summer, acclimated to 24 °C. Each group consisted of six captive males that were first housed singly for 2 days and later allowed to interact with other shrews of the same group. Our analysis revealed all group mates were frequently found huddling in the same shelter, regardless of acclimation temperature. However, mass-adjusted resting metabolic rate decreased in winter shrews with larger huddle sizes and remained constant in summer shrews in huddles with three or more individuals. Body temperature was also significantly lower and more varied in winter shrews. After being group-housed, winter shrews used less torpor and significantly increased their body mass and food intake in the first days. Our results suggest that temperature had a small influence in huddling behavior but a large one in physiological factors, such as metabolism, body temperature, and food intake, after shrews started interacting socially. Therefore, social thermoregulation provides benefits to C. russula besides energy savings. Small mammals often huddle to reduce thermoregulation costs during cold. Previous studies in wild greater white-toothed shrews suggested that this species only employs social thermoregulation in the colder months of the year. We captured wild shrews and assessed the energetic advantages of this social thermoregulation strategy under controlled conditions. We confirmed that social thermoregulation indeed has more energetic benefits to shrews in winter than in summer. However, huddling between individuals still occurs at warm temperatures, when energetic benefits are no longer significant. Such observations suggest that huddling is advantageous to shrews in multiple ways beyond thermoregulation. Furthermore, social interaction between individuals influenced daily torpor, body mass, and feeding, further supporting the hypothesis that sociality in greater white-toothed shrews has direct and indirect effects on their energy budget.