Seasonal Changes in Agonistic Behavior of Clethrionomys gapperi in Southeastern Manitoba and Its Possible Relation to Population Regulation

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Abstract
Behavioral encounters between pairs of wild-trapped, redbacked voles (C. gapperi) of the same sex were observed regularly in a neutral arena throughout 1974 at Pinawa, Manitoba. The study occurred during the peak phase of a 4-yr cycle. Behavioral acts (19) were recorded and grouped into 5 components (amicable behavior, vocalization, avoidance, attack behavior and retaliation). Levels of interaction (LI) and intensities of aggression (IA) were computed monthly. Increases in LI and IA were evident in each sex following sexual maturation, and the recruitment of young-of-the-year. Adult males were significantly more aggressive (LI and IA) than adult females in winter and prior to recruitment of young in summer; but during late summer, male young-of-the-year were significantly more aggressive than any other age/sex class. Increases in IA paralleled increases in LI and were associated with breeding, recruitment and a young population age structure, increased density and heavy mortality, and female territoriality. Functions of aggressive behavior appear to differ with sex. In males aggression may operate in mate acquisiton dispersal and interspecific segregation.In females aggression may act to maintain mutually exclusive territories, which increases inclusive fitness by maximizing reproductive success. This is achieved presumably by limiting resource utilization in the defended area to kin, thereby forming the basis of a possible population-regulating mechanism. Such a hypothesis requires experimental verification and would only act in the absence of other limiting factors.

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