Torpor is an energy saving strategy achieved by substantial reductions of metabolic rate (‘MR') and body temperature (‘Tb'), which enables animals to survive periods of low resource availability. Social thermoregulation or ‘huddling' can act in synergy with torpor, allowing individuals to maximize energy savings. These strategies are crucial for juveniles, which might not have enough time, especially when born late during the reproductive season, to accumulate large amount of fat reserves before winter start. Hibernation or multiday torpor is regularly interrupted by periods of rewarming, i.e. arousals, which are highly energetically costly, and characterized by high levels of Tb and MR. The garden dormouse (Eliomys quercinus) relies on body fat stores to fuel hibernation, but can also feed during winter. We investigated in late-born juvenile garden dormice (1) the effect of huddling on torpor patterns and body mass (‘BM') changes according to winter food availability, (2) the dynamic of huddling behavior during hibernation, and (3) the individual energetic impact of huddling during a single arousal. We observed a significant negative effect of food availability on torpor use, which was surprisingly stronger in males. Further, MR of dormice fed ad-libitum was greater in torpor and during euthermia, and overwinter BM loss was identical between fed and fasted individuals. Although huddling reduced energy exchange and BM loss of individuals during a single arousal, it had no effect on either hibernating patterns or BM loss over the entire winter. Nevertheless, grouped dormice had lower MR in torpor than single individuals. Our investigation of the dynamic inside a huddle further revealed a ‘random-like mechanistic' behavior along winter; arousal from torpor was not always initiated by the same individual, and BM did not determine the rank of arousal among individuals within the huddle. During hibernation, huddled animals were taking turns to actively rewarm, hence sharing costs and benefits over winter. We conclude that the dynamic of social thermoregulation during hibernation seems to counter-balance its energetic benefit during torpor and periodic arousals.[-]