Study animals and procedures
We kept one male and one female dormouse in outdoor captivity near the area where they were born, in the southernmost zone of the Iberian population of the species (Montnegre range). Adult dormice here have a weight of 150-200grs. The climate in this area is Mediterranean, with average temperatures of 15.85 ºC (S.E. = 0.14, range: 0.47 ºC − 34.11 ºC) and 800-900mm rainfall. All individuals were 1y old when they entered the cage. Despite being sexually mature, they did not engage in reproduction during the study. The cage was ca. 6m3 in size and it was set outdoors. Two nest boxes as those used in our field study (Freixas et al. 2012) were available for dormice, and food (mainly dry seeds of oak, chestnuts, hazelnuts and apple) was provided ad libitum. Dormice performed hibernation in a refuge underground specifically set for this purpose, as they mostly do in the wild. Data was collected automatically by a temperature data-logger (iButton® DS1922L-F5, accuracy: ± 0.5 °C, sampling frequency: 1/hour). Devices were surgically implanted intraperitoneally for an almost year-long period (341 days, 8192 temperature records for each individual). We recorded air temperature at the exact same time intervals also using an iButton device.