Huddling by rat pups: Group behavioral mechanisms of temperature regulation and energy conservation

Body heat loss was attenuated and oxygen consumption was reduced by hud-dling in litters of developing rats. Rat pups derive physiological benefits from huddling similar to those enjoyed by adult mammals; these findings contrast with previous characterizations of the altricial rat as poikilothermic. Huddling insulates by lessening the exposed body surface area of the participants, thus retarding heat loss and enhancing the efficiency of thermogenesis. These physical mechanisms of the clump are actively regulated by the pups. A novel quantitative measure of huddle size revealed a form of group regulatory be-havior in rat pups whereby the surface expanded and contracted with in-creases and decreases in ambient temperature. The individual basis of this group regulatory activity was investigated by marking individual pups and ob-serving them in huddles by means of time-lapse videography. It was found that individual animals circulate through the huddle, frequently exchanging locations in the group. By studying the huddle positions of an anesthetized pup and a marked control sibling, dynamics of the pup flow were clarified. Or