The hazel dormouse is mainly an arboreal species with nocturnal habits that, in northern European countries, moves down to the ground to hibernate in the autumn where they stay until spring at locations not well understood. To prepare for hibernation, dormice accumulate fat reserves necessary to maintain vital bodily functions when food supply is lower and the energy cost of staying active exceeds the amount of energy that can be harvested in their habitat. Little is known about the hibernation ecology of hazel dormice or where they go in the winter. in this study, different methods to identify dormouse hibernacula were used: telemetry, systematic searches, and wildlife detection dogs. The movements of 31 individuals prior to and during hibernation were observed using radiotelemetry. Weight measurements of eight wild hazel dormice were recorded during the hibernation period and the rate of weight loss of each individual calculated as proportion of body mass per day. A total of 44 hazel dormouse hibernacula were identified: 24 by telemetry, 20 by systematic searches and none by wildlife detection dogs. Telemetry results indicated that dormice selected sites for their hibernaculum within 43 m (SD=30) from the place where they were captured while active, suggesting that hibernation normally takes place within their home range. The timing of hibernation varied amongst individuals, with some dormice remaining active and feeding throughout the month of December. On average dormice lost 0.47% of their body mass per day during hibernation bouts. Despite dormice hibernating largely in leaf litter on the woodland floor, often at conspicuous locations, detecting hibernacula without the use of radiotelemetry proved labour intensive but possible through systematic searches. The fact that hazel dormice lose a relatively high proportion of their body mass during the winter highlights the challenges wild animals face to survive hibernation.