Female-biased natal dispersal in the Siberian flying squirrel

Natal dispersal is usually sex biased in birds and mammals. Female-biased natal dispersal is the prevailing pattern in birds but is rare among mammals. Hypotheses explaining sex bias in dispersal include the mate-defense mating hypothesis, which predicts male-biased dispersal, the resource-defense hypothesis predicting female-biased dispersal, and the competition hypothesis, which predicts that if dispersal is caused by competition for resources between sexes, then the subdominant sex will disperse. We studied natal dispersal of Siberian flying squirrels Pteromys volans using radio telemetry in Southern Finland in 1996--2004. Of 86 juveniles that survived over the dispersal period, almost all young females dispersed from the natal site, whereas almost 40% of males were philopatric. Dispersal was farther for females than males. Females began dispersal on average 2 weeks earlier than males and were lighter in mass at the onset of dispersal than later dispersing males. No mate- or resource-defense mating system could be found among males, but females seemed to defend nest and apparently food resources, in contrast to the expectation of dispersal bias in resource-defense systems. Competition for resources between sexes does not explain female bias either: in the flying squirrel, the female seems to be the dominant sex. We propose that young females are subordinate to their mothers and have to disperse to find a vacant, suitable site for reproduction. Copyright 2009, Oxford University Press.