Huddling by rat pups: multisensory control of contact behavior.

Huddling, or clumping behavior, begins in the litter situation and persists throughout the adult life of the rat (Rattus norvegicus). In pups, as in adults, the behavior provides a metabolically important means of reducing heat loss. The sensory stimuli that elicit, direct, and maintain huddling in developing rat pups (5-20 days of age) were studied in a standardized testing situation by using long-term time-lapse video observations. All pups huddled with a single, immobile sibling. A loop of warm tubing also elicited huddline. However, it appears that other, nonthermal cues can elicit huddling, since a dead, ambient-temperature pup was a sufficient stimulus for the behavior. Disruption of normal olfactory input by intranasal infusion of zinc sulfate interfered with the maintenance of contact. In addition, two kinds of tactile stimulus, vertical contours and furry "comfort" cues, as well as photic responses appeared to participate in the mediation of huddling. Huddling in the altricial rat is under multisensory control, although the number of cues used by pups for huddling appears to increase with age.