Communal nesting in an ‘asocial’ mammal: social thermoregulation among spatially dispersed kin

Abstract

Communal nesting can help defray the high cost of endothermic heat production in cold environments, but such social behavior is generally thought to be incompatible with the persistent defense of exclusive territories in typically ‘asocial’ animals. We examined the propensity for communal nesting in female red squirrels (Tamiasciurus hudsonicus), which maintain individual year-round territories, through intensive monitoring of litters over 22 years and by radio-tracking females during 3 years in late winter/early spring. Communal nesting was exceptionally rare during lactation: of 1,381 litters tracked to emergence, we observed a single instance in which two closely related (r = 0.5) females pooled their litters into a single nest. In contrast, nest sharing between 2–3 females was relatively common in the late winter/early spring, prior to mating; at least 12 of 63 females (19 %) engaged in communal nesting during a year of systematic tracking of radio-collared females from late February to April. Communal nesting occurred more frequently when temperatures were colder, suggesting that such aggregations might function to reduce thermoregulatory costs. These social associations were typically, though not exclusively, between closely related individuals (r ≥ 0.25 for seven of eight cases; mother–daughter dyads: four of eight), suggesting this cooperative behavior might evolve through kin selection and/or may reflect extended parental care. Our results demonstrate that female red squirrels engage in communal nesting, typically with closely related kin, despite a dispersed population structure that stems from the persistent defense of individual territories.