Seasonal dispersal in a seminatural population of Peromyscus maniculatus

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Abstract
Social factors contributing to seasonal patterns of dispersal in Peromyscus maniculatus bairdi were tentatively identified by partial control of the initial demography, nutrition, predation, and competition. Populations consisting of eight mated pairs of adult mice were established in an open field artificially provided with favorable microhabitats during two springs, one summer, and two falls. The microhabitats were 32 aluminum cylinders 2 m in diameter arranged in 16 couplets on a square grid covering 1.4 ha. Each cylinder enclosed an area of 3.1 m2 containing nest boxes, food, water, and a single small exit to the surrounding fields. Nests were checked every 3rd day for marked individuals over a period of 10 weeks, after which the existing population was removed and a new one established. More individuals were lost from the population during spring and summer than in the fall. Local movements on the study area were not related to the disappearance of mice. Significantly more mothers moved nests between litters than remained. Family groups were most cohesive in fall and were rarely joined by nonrelatives. There was no evidence of agonistic behavior within families. Most mice left the population in the spring and summer when the juveniles were sexually maturing, in contrast to the fall when only the resident adults continued to breed. A sexual search hypothesis proposes that the rate of dispersal increases directly with the rate of recruitment of sexually maturing individuals.