A comparative analysis of huddling in infant Norway rats and Syrian golden hamsters: does endothermy modulate behavior?

In infant rats, huddling improves surface-to-volume ratios and provides metabolic savings during cold exposure. It is unclear, however, whether endothermy is also a necessary component of huddling. In the present experiment, huddles composed of infant Norway rats (2- or 8-day-olds), which produce heat endogenously, or Syrian golden hamsters (8-day-olds), which do not produce heat endogenously, were exposed to decreases in air temperature. Behavioral and physiological responses were monitored throughout the test. Rats, especially at 8 days of age, were better able to thermoregulate using huddling than hamsters, due in part to endogenous heat production. Furthermore, 8-day-old rats exhibited behavioral responses that promote heat retention, suggesting that both physiological and behavioral mechanisms contribute to effective thermoregulation during huddling in the cold.