NATAL DISPERSAL AND PHILOPATRY IN PRAIRIE VOLES (MICROTUS-OCHROGASTER) - SETTLEMENT, SURVIVAL, AND POTENTIAL REPRODUCTIVE SUCCESS

We analyzed the costs and benefits of natal dispersal and philopatry in a free-living population of the prairie vole, Microtus ochrogaster, in which 70% of the males and 75% of the females were philopatric. Rather than settling into a nest, 40% of male dispersers continued to wander throughout the study area, while only 13% of female dispersers did so. Whereas males were more likely to wander in spring-early autumn during low density periods, females were more likely to wander during spring-early autumn, irrespective of population density. Of those animals that settled into a nest, females were more likely than males to settle as single individuals. Same-sex siblings that dispersed commonly joined the same social group. Although often settling within 5 m of each other, opposite-sex siblings that dispersed never joined the same social group or formed a male-female pair. Total length of life was longer for males and females that dispersed than for those that remained at the natal nest. Animals survived longer after dispersal if they settled greater than or equal to 30 m from the natal nest than if they settled less than or equal to 30 m from the natal nest. Length of survival following dispersal was not correlated with age at time of dispersal. Fitness of female dispersers was 2.5 times that of philopatric females, estimated by comparison of the percent becoming reproductive, survival time after becoming reproductive, and the estimated number of female offspring per litter that survive to adult age. The success of dispersers may be related to the high food resource habitat in which the study was conducted.