Demography and dispersal of thirteen-lined ground squirrels in relation to prairie dogs in Colorado shortgrass steppe

In northern Colorado, thirteen-lined ground squirrels (Spermophilus tridecemlineatus) are less numerous in colonies of black-tailed prairie dogs (Cynomys ludovicianus) than in surrounding grassland areas, but the ecological factors responsible for this difference are unknown. In 2005, I trapped squirrels on and adjacent to a 70-ha colony to compare relative abundance and demographic variables in and out of colonies. Adult and juvenile weight, female productivity, natal range areas, and number of reproductive adults did not differ. However, squirrels were more abundant, juveniles moved from colony to grassland and more juveniles were caught during the first week post-emergence outside of the colony. Although some aspects of the population ecology of squirrels were similar, differences in demographic variables and abundance suggest that colonies may be poorer quality habitat.;It has been argued that sociality influences the degree of male-bias in juvenile dispersal in North American ground squirrels. Thirteen-lined ground squirrels are relatively asocial, but no estimates of juvenile dispersal are available to assess whether dispersal is less male-biased than for other squirrels. In 2006, I radio-collared 15 male and 14 female juvenile squirrels. Four (27%) males dispersed, while none of the females dispersed. As expected based on their sociality, dispersal in S. tridecemlineatus was only weakly male-biased. However, a re-examination of published dispersal rates of other Spermophilus suggests that sociality explains little variation in sex-biased dispersal. Instead, length of active season and habitat type were better predictors of the degree of male-bias in dispersal. Environmental factors likely influence both sociality and sex-biased dispersal in Spermophihus.