Costs and benefits of sociality in yellow-bellied marmots (Marmota flaviventris): do noncolonial females have lower fitness?

Whether an animal lives alone or in a group may have fitness consequences. Among yellow-bellied marmots (Marmota flaviventris), fitness is thought to be lower for noncolonial than for colonial females because juvenile survival, as indicated by trapping, is lower. Trapping, however, may not be an accurate estimate of survival. Low recapture rates of noncolonial juveniles may result from early dispersal due to maternal behavior, or higher mortality due to predation or inadequate resources for overwinter survival. Our objective was to determine if survival was lower for noncolonial than for colonial juveniles, and to determine the cause of the low recapture rate of noncolonial juveniles. Our results show that survival of noncolonial juveniles was not lower than that of colonial juveniles. Noncolonial juveniles were not more vulnerable to predation during the active season, nor was overwinter mortality higher. Some noncolonial juveniles did disperse early, and most moved away from the natal burrow to hibernate, thereby explaining the low recapture rate reported previously. Early dispersal was not related to maternal behavior. Noncolonial females do not enjoy the benefits of group-living, especially the opportunity to form matrilines; but they also do not suffer the costs, such as competition for resources.