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We used intensive livetrapping to examine natal dispersal and philopatry in prairie voles (Microtus ochrogaster). The majority of male (70.0%) and female prairie voles (75.1%) remained at the natal nest until death. Those males and females that did disperse left home at about the same age (45-55 days) and moved similar distances (28 33 m). Dispersal was more common (1) from small natal groups than from large natal groups, (2) following disappearance of parents, (3) during the breeding period than during the nonbreeding period, and (4) at low population densities than at high densities. Dispersal was not associated with level of competition for mates within natal groups, and dispersers did not differ from nondispersers in body weight. Our data do not support competition for mates or resources as important factors influencing natal dispersal in prairie voles. The absence of sex differences in dispersal tendency or distance, and our finding that more than half of dispersers had become reproductive before leaving the natal nest, lead us to suggest that inbreeding avoidance is not a primary function of dispersal in this species. Dispersal was, however, more common when potential mates within the natal group were relatives than when they were nonrelatives. Although not tested here, if family members avoid mating with one another through patterns of mate choice, then some animals may leave home in search of mates. The precise benefits associated with philopatry in prairie voles remain to be identified.

MCGUIRE, B., PIZZUTO, T., and GETZ, L. L. 1990. Potential for social interaction in a natural population of prairie voles (Microtus ochrogaster). Can. J. Zool. 68: 39 1-398. Many hypotheses on the role of social behavior in population regulation of microtine rodents assumethat social interactions are more frequent at high density than at low density. We evaluated this assumption by measuring potential for social contact in a population of prairie voles (Microtus ochrogaster). Our livetrapping regime monitored presence of resident and nonresident animals at the periphery of home ranges of social groups. Resident adults and young of both sexes were captured at home range boundaries. Potential for social interaction with nonresidents was greater at the periphery of home ranges than at nests. Intruders tended to be male adults from neighboring social groups. Presence of adult males in the resident group played an important role in deterring visits by nonresident males. During the spring, summer, and autumn reproductive period, number of captures of nonresident males, but not females, showed a strong positive relationship with population density. Despite relatively high densities during the winter nonreproductive period, there were few captures of residents and nonresidents at the periphery of home ranges. We conclude that the relationship between potential for social interaction and population density varied as a function of sex and season. MCGUIRE, B., PIZZUTO, T., et GETZ, L. L. 1990. Potential for social interaction in a natural population of prairie voles (Microtus ochrogaster) . Can. J . Zool . 68 : 39 1 -398.Plusieurs hypothitses sur le r61e du comportement social dans le contr6le dkmographique des rongeurs microtinks supposent que les interactions sociales sont plus frkquentes lorsque la densit6 de la population est ClevCe que lorsqu'elle est faible. Nous avons tent6 d'kvaluer cette supposition en mesurant la probabilitk des contacts sociaux chez une population de Campagnols des prairies (Microtus ochrogaster). Notre systkme de piCgeage de campagnols vivants permettait d'enregistrer la prCsence des individus rksidants et des individus non rCsidants a la pCriphCrie du domaine vital de groupes sociaux. Des adultes rCsidants et des jeunes des deux sexes ont Ct C capturCs en bordure du domaine vital. La probabilitk des interactions sociales avec des individus non rksidants s'est avCrCe plus ClevCe en pCriphCrie du domaine vital qu'au nid. Les intrus Ctaient gCnCralement des miles adultes provenant de groupes sociaux avoisinants. La prksence de mdles adultes au sein d'un groupe rksidant CtCit un important facteur de dktournement de miles non rksidants. Au cours des saisons de reproduction du printemps, de I' CtC et de l'automne, le nombre de captures de miles non rksidants Ctait en corrklation trks forte avec la densit6 de la population; cette relation n'a pas Ct C constatke dans le cas des femelles. En dCpit des densitCs relativement ClevCes en hiver, au cours de la pCriode inactive de la reproduction, le nombre d...

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