Communal nesting behaviour of Siberian flying squirrels during the non-winter season

Communal nesting behaviour of small mammals is thought to function mainly as a method of thermoregulation. However, this behaviour is also observed during the non-winter season when there are no obvious thermoregulatory benefits. Siberian flying squirrels (Pteromys volans) nest communally during the non-winter season. This may facilitate mating, but other functions such as thermoregulation have not been sufficiently studied. Therefore, we examined whether communal nesting of P. volans during the non-winter season plays a role in thermoregulation in addition to mating. In the event that communal nesting in the non-winter season has any function other than mating, we expected an increase in non-mating groups consisting of only-males during the nurturing period (duration of mother squirrel and cubs living together) because females rearing their young do not participate in communal nesting. In Obihiro, Hokkaido, Japan, during the non-winter season (May–October) between 2019 and 2021, we captured P. volans in 252 nests by using nest boxes. The occurrence of male-only groups showed a tendency to increase during the nurturing period. Moreover, the number of mixed-sex groups increased between August and October each year; these changes in communal nesting during the non-winter season were unrelated to the variation in air temperature or precipitation. These results suggest that during the non-winter season, communal nesting of P. volans is related to reproductive behaviour. Additional studies are needed to determine how communal nesting during the non-winter season enhances the reproductive success of male and female P. volans.