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According to kin selection and inbreeding avoidance hypotheses, natal dispersal should be facultatively adjusted to balancing the costs and benefits of mother–offspring interactions. In polygynous mammals, it is hypothesized that female offspring should seek to avoid local resource competition with their mother, whereas male dispersal should be determined by inbreeding avoidance. We tested these hypotheses with a field experiment investigating the relationship between territory acquisition and mothers presence in the root vole Microtus oeconomus. This species has a flexible social system in which sisters and mothers home ranges overlap substantially, whereas sons disperse to a greater extent. Immature sibling voles aged 20 days were released for 20 days together with an unrelated adult male in a 2-patch system either in the presence of their mother or in the presence of an unrelated adult female. Offspring movements were not influenced by mothers presence, but offspring, especially females, avoided the patch occupied by the adult female irrespective of kinship. Offspring remaining in contact with their mother were reproductively suppressed at the middle, but not by the end, of the experimental period. These results indicate that juvenile root voles adopted an opportunistic settlement strategy where they avoided the adult female irrespective of kinship and inbreeding risks. [ABSTRACT FROM AUTHOR]