<p>Reproductive costs in mammals are often associated with various changes in spatial structure of populations during breeding period, typically accompanied by an increased probability of social interactions. In this study, we investigated elements of social behaviour and their association with breeding period in a solitary species, the edible dormouse (<i>Glis glis</i>), on the periphery of the range. We evaluated the number of dormice detected in nest boxes, found sleeping as single individuals or in groups. The frequency of huddling behaviour here was markedly lower than in other regions (9.7% of all dormice detections), with maximal group size of five individuals. Huddling occurred more frequently during the mating period than at the end of the summer season and was more common in males than in females. High level of serum testosterone in males could influence the sociality in different ways. It typically increases aggression in males, while simultaneously requiring maintenance of high body temperature through group formation. Reproductively active males were encountered in huddles more frequently. The factors raising probability of huddling behaviour in males and females were reproductive state, lower body mass, and lower masting of tree seeds. Temperature and humidity affected males and females in different ways: group formation in males was more likely at lower temperature and humidity, while in females it increased under warmer and more humid conditions. Also number of dormice in a given year influenced on huddling in males. Overall, huddling in this peripheral population appears to reflect thermoregulatory demands linked to reproduction physiology and post-mating energetics, rather than direct increases in sociality during pairings. This may be caused by suboptimal environmental conditions in the peripheral population, affecting metabolic rate, spatial structure and behaviour.</p>