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 i n a free-living population of the prairie vole, Microtus ochrogaster, in which 70% of the males and 75% of the females were philopatric. Rat her than settling into a nest, 40% of male dispersers continued to wan der throughout the study area, while only 13% of female dispersers did so. Whereas males were more likely to wander in spring-early autumn d uring low density periods, females were more likely to wander during s pring-early autumn, irrespective of population density. Of those anima ls that settled into a nest, females were more likely than males to se ttle as single individuals. Same-sex siblings that dispersed commonly joined the same social group. Although often settling within 5 m of ea ch other, opposite-sex siblings that dispersed never joined the same s ocial group or formed a male-female pair. Total length of life was lon ger for males and females that dispersed than for those that remained at the natal nest. Animals survived longer after dispersal if they set tled greater than or equal to 30 m from the natal nest than if they se ttled less than or equal to 30 m from the natal nest. Length of surviv al following dispersal was not correlated with age at time of dispersa l. Fitness of female dispersers was 2.5 times that of philopatric fema les, estimated by comparison of the percent becoming reproductive, sur vival time after becoming reproductive, and the estimated number of fe male offspring per litter that survive to adult age. The success of di spersers may be related to the high food resource habitat in which the study was conducted.