Fighting, Maturity, and Population Density in Microtus pennsylvanicus

Abstract

A study of a population of Microtus pennsylvanicus was conducted in Wayne County, Pennsylvania, using snap-traps. Densities probably were between 100 and 200 per acre in 1968 and half that in 1969. Inhibition of growth and maturation were seen in both years but was greater in 1968. Fighting between males, as indicated by the prevalence and severity of wounds, was severe in 1968 but reduced the following year. Male voles, with rare exception, were not attacked or did not fight until testicular weight was more than 900 milligrams and seminal vesicular weight greater than 100 milligrams. Thus voles in which maturation was inhibited showed essentially no evidence of having been attacked or having fought. Changes in rate of maturation with density may explain many of the observed differences in the tolerance of young males by old male voles.