Survival of cohorts in a fluctuating population of the vole Microtus townsendii


  • Terry D. Beacham

    1. Institute of Animal Resource Ecology, University of British Columbia, 2075 Wesbrook Place, Vancouver, BC, Canada
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    • *Marine Fish Division, Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, Nova Scotia, Canada B2Y 4A2.


Survival patterns of cohorts are described during a population cycle of the vole Microtus townsendii near Vancouver, British Columbia, Canada. A two–year live–trapping study on both enclosed and unfenced populations showed that cohorts during the increase phase of growth lived longest and had the best survival. Smaller voles in the peak density spring cohort had poor survival, but survival increased during the peak density summer. Survival of cohorts in the decline phase breeding season was very poor. The suggestions are made that changes in spacing behaviour may cause changes in cohort survival and that the causes of rapid changes in survival need to be determined.