Age of Weaning in Two Subspecies of Deer Mice

Weaning age in deer mice is defined as the age at which the young mice maintain or gain weight during a 24-hour period of isolation; mice younger than weaning age lose weight. Two subspecies of deer mice differed in weaning age; the age for Peromyscus maniculatus bairdii was 18 days; for P. m. gracilis, 24 days. Age and food consumption were better predictors of the weaning condition, as defined in terms of weight change with isolation, than body weight.