Environmental and population correlates of variation in short torpor use by wild hazel dormice (Muscardinus avellanarius).

Torpor is a life history strategy for conserving energy during unfavourable conditions. Hazel dormice Muscardinus avellanarius are known for prolonged winter hibernation but also employ short bouts of torpor of less than 24 hrs, independently of hibernation. In Great Britain, at the edge of the species' range, there is marked spatial and temporal variation in short torpor among individuals and among populations, the causes and consequences of which are not well understood. We quantified variation in torpor use in the dormouse active season and identified individual and population-level correlates of torpor frequency. We analysed the data from the National Dormouse Monitoring Programme, comprising 53,953 observations of adult dormice in nest boxes on 381 sites over 25 years. Short torpor was more frequent at sites towards western Britain, at greater elevation, with more ancient woodland, and greater connectivity of broadleaf woodland. Dormice were more frequently torpid on colder and wetter days, and within colder and wetter seasons. Adult dormice observed in boxes containing young were rarely torpid, while adults alone were more frequently torpid. Lighter individuals were more frequently torpid earlier in the season (April-August) and heavier individuals later (September-October). Sites where short torpor was more frequent had lower counts of dormice and lower counts of breeding events. As a response to short and long-term variation in environmental conditions, short torpor is likely a mediator of environmental drivers of dormouse population dynamics. This is of particular relevance under climate change and at range edges, which already experience adverse environmental conditions.