Environmental temperature modulates onset of independent feeding: warmer is sooner

Individual dams and their litters were observed from Days 14-22 in a seminatural environment consisting of a nestbox attached to a larger, open field in which powdered chow was available. Ambient temperature in the field was either warm (30”C), moderate (21”C), or cold (10°C); nest temperature was always moderate. Behavior was monitored 12 hr/day by time-lapse video recording. The pups ’ egressions into the field and onset of independent feeding were temperature-related: Weaning was earliest in the warmth and increasingly late with decreasing ambient temperature. Among subjects in the cold condition, there was a positive correlation between duration in the field and duration feeding. Pup growth was unaffected by the temperature regimes. Environmental temperature has emerged as a determinant for early nest egressions and weaning onset. 0 1996 John Wiley & Sons, Inc. The drama and the universality of weaning reflects its fundamental significance in mammalian development. The transition from suckling to independent feeding is vital to offspring survival and growth. Adults also derive benefits from weaning because they can re-allocate their parental resources to subsequent propagules. The weaning process consists of the disappearance of suckling and the development of solid food intake. Suckling by Norway rats (Rattus noruegicus) in the laborator