Natal philopatry and kin groups in woddchucks (Marmota monax) [Philopatrie natale et apparentement des groupes de marmottes commune d'Amérique (Marmota monax)].

Résumé

In mammals, particularly ground dwelling sciurids, kin selection is the most commonly proposed route to sociality. Ecological constraints (e.g., limited habitat) may favor delayed dispersal and natal philopatry, creating a population of related individuals. One approach to understanding evolution of sociality is to study facultatively social species, in which differences in current ecological conditions lead to differences in social organization. Marmots (Marmota spp.) display a continuum of sociality, and woodchucks (M. monax) lie near the asocial end of the continuum. Yet, they also display behavioral flexibility across populations. I have studied a relatively high density population of woodchucks in southern Maine since 1998. This population occupies a wildlife sanctuary surrounded by an estuary, a 3-lane highway and housing developments; thus, animals may face limited dispersal opportunities favoring natal philopatry and delayed dispersal. I used behavioral observations and radiotelemetry to document dispersal and kinship patterns and to relate such patterns to ecological conditions. Nearly 50% of juveniles disappeared from the study site in their first summer. However, 53% and 39% of males and females, respectively, remained in their natal range through the first summer. Data also suggested that 2-4 siblings hibernated jointly, perhaps with their mothers. In their second summer, 35% and 47% of philopatric males and females, respectively, were recruited into the population, often settling within 1 home range of their natal range. Such settlement patterns produced clusters of kin from more than 1 generation. Thus, contrary to many published accounts, some juvenile woodchucks in this population remained philopatric, either postponing dispersal for a year or being recruited into the population, and equal numbers of males and females were philopatric. Dispersal may be constrained by limited amounts of suitable habitat in this suburban environment.