Adrenocortical Activity in Two Meadow Vole Populations

The object of this study was to observe the relation between population density and adrenocortical activity, as measured by adrenal weights and blood eosinophil levels, in free-living populations of the meadow vole, Microtus pennsylvanicus. The study was initiated to test the hypothesis presented by Christian (1950) that high population density constitutes a stress factor eliciting a response from the adrenopituitary systems of individuals making up the population and thus brings about the occurrence of the General Adaptation Syndrome of Selye (1946). The study was begun in the late summer of 1952 and extended through the fall of 1953. Two widely separate areas were chosen after inspecting a large number of areas in the vicinity of Madison, Wisconsin, for evidences of high meadow vole populations. One area, called the Mud Lake Area, had a very high population in the fall of 1952, while the other, the Hammersley's Marsh Area, had a low to normal population at this time.