Characteristics of Dispersing Meadow Voles Microtus pennsylvanicus

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Abstract
A population of meadow voles M. pennsylvanicus in Minnesota [USA] exhibiting annual rather than multiannual fluctuations in density was studied. To characterize voles of different movement patterns, data on sex, age, reproductive condition and genotype at 2 polymorphic loci (Tf and LAP) were collected in summer (n = 1323) and autumn (n = 1191) during 2 consecutive years. Three movement patterns were identified: dispersers were those voles that moved onto grids from which all trapped Microtus were removed; residents were those voles found on the same grid during at least 2 trapping periods; movers were those voles known to move long distances within a population. Dispersers differed from residents most consistently by being more likely to be young. Although dispersers also differed from residents both reproductively and genetically, the differences were not consistent for all age-sex groups throughout the study. Movers were an identifiable subset of residents that differed from dispersers and other residents during summer by being more likely to be adult males. During the breeding season, female residents were the most stable subset of the population; adult males tended to move long distances within the population. Young females tended to disperse close to the time of initiating reproductive activity; young males tended to disperse as nonreproductives. During the nonbreeding season, dispersers were more nearly a random subset of residents.