Huddling and food availability shape seasonal torpor and energetics of juvenile garden dormice.

Environmental fluctuations challenge juvenile hibernators to efficiently balance growth, fattening, and energy conservation prior to their first winter. This study investigates how social thermoregulation (huddling) and food availability affect the use of torpor, growth, fat accumulation, and hibernation in late-born juvenile garden dormice. Juveniles exhibited flexible energy-saving strategies, with huddling influencing torpor patterns and food intake during pre-hibernation. Despite these behavioral differences, individuals reached similar body mass and size at the onset and end of hibernation, regardless of housing or feeding conditions. During hibernation, food availability modulated total energy expenditure, particularly in males, likely due to changes in reproductive investment. These findings suggest that the combined use of torpor and huddling provides developmental flexibility, enabling juvenile dormice to meet the energetic demands of early life. This plasticity may be critical for survival in the face of environmental unpredictability, and future studies should investigate how early-life energy strategies influence long-term fitness and reproduction success.