EVIDENCE FOR FEMALE-BIASED DISPERSAL IN NORTH-AMERICAN PORCUPINES (ERETHIZON-DORSATUM)

Although sex biases in natal dispersal are well known among birds and mammals, female-biased dispersal in polygynous mammals is rare. North American porcupines are polygynous and recent evidence suggests that n atal dispersal in this species may be female-biased. We used data on d isappearances, immigration, and reproductive behaviours to characteriz e natal dispersal and examine the extent to which inbreeding avoidance may motivate natal dispersal in porcupines. We predicted that, if fem ale porcupines were the predominant dispersers, rates of disappearance and immigration would be higher for females than for males. Also, if females disperse to avoid mating with fathers, then the mean age of fe males at first conception should be less than the mean residence time of adult males. Population data suggested that natal dispersal was fem ale-biased because a higher proportion of females (31%) disappeared th an males (11%), and 78% of 18 immigrants observed in the population we re females. Data on pregnancies indicated that female age at first con ception (approximate to 25 months) was less than the mean residence ti me of adult males (approximate to 36 months), suggesting that female p orcupines may disperse to avoid incestuous matings with fathers. Littl e is known regarding potential resource competition between mothers an d offspring, or on how philopatric males avoid mating with their mothe rs. Additional data are needed in these areas to interpret dispersal t endencies in porcupines.