The spring decline in the meadow vole, Microtus pennsylvanicus: the effect of density

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Abstract
The densities of six Microtus pennsylvanicus populations were reduced by removing large, sexually mature adults 6 months prior to (fall removal manipulation) and just prior to (spring removal manipulation) anticipated spring declines. When the spring decline on the control grid was a result of short distance dispersal, the manipulations had no effect; when it was a result of in situ mortality and (or) long distance dispersal, the fall removal manipulation produced a significant improvement in the survival rates of adult males. Adult female survival rates were high and unaffected by the manipulations. Adult reproductive rates were high and similar on all grids. The onset of the females' breeding season was advanced by the manipulations in two trials. Home range sizes were similar for all animals during the nonbreeding period. During the breeding period, males and females on the experimental grids had larger home ranges than those on the control grids.