Manipulation of Female Behaviour in Field Populations of Microtus townsendii

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Abstract
The behavior offemale M. townsendii was manipulated in field populations during a spring decline in numbers. All females were implanted with testosterone to increase aggressiveness in one area, and force-fed the chemosterilant mestranol to reduce aggressiveness is another area. Testosterone treatment resulted in wounding among females, increased size of female home ranges, a reduction in female survival and increased female immigration. Males in the population with testosterone-treated females had the same population dynamics as males in a control population and a population with no females. Mestranol treatment had no effect on female dynamics. Males with mestranol-treated females survived better than control males. In spite of the profound effect of testosterone on social strife, the spring decline in numbers was little affected by these experiments. Female spacing behavior may operate in more subtle ways than overt aggression.