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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.

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Populations of 2 species of arvicoline rodents, the prairie vole (Microtus ochrogaster) and meadow vole (M. pennsylvanicus), were monitored monthly in alfalfa, bluegrass, and tallgrass prairie habitats in east-central Illinois from 1972 through 1997. Alfalfa provides very highquality preferred food and poor vegetative cover for both vole species, whereas bluegrass provides intermediate food and vegetative cover. Preferred food resources were very low, especially for M. ochrogaster, and vegetative cover was very dense in tallgrass prairie. Maximum and mean population densities of M. ochrogaster were highest in alfalfa, intermediate in bluegrass, and lowest in tallgrass prairie. Populations of M. ochrogaster displayed synchronous 3-to 4-year multiannual cycles in all 3 habitats. Cycles were most pronounced in alfalfa, less pronounced in bluegrass, and barely discernible in tallgrass prairie. Food availability seems more important than vegetative cover for the success of M. ochrogaster. Densities of M. pennsylvanicus generally were very low in bluegrass and alfalfa habitats, both of which contained an abundance of preferred food plants. When M. pennsylvanicus was present in abundance in these 2 habitats, populations displayed annual or erratic fluctuations. Densities of M. pennsylvanicus were much higher in tallgrass prairie than in the other 2 habitats. Although vegetative cover seems more important than food availability for the success of M. pennsylvanicus, no evidence existed for population cycles in tallgrass prairie. We found no synchrony among population fluctuations of the 2 species of voles in the 3 habitats.

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