Demography of Snowshoe Hare Populations in Wisconsin

Abstract

During March 1980–August 1981, snowshoe hares (Lepus americanus) were live-trapped near the species' southern geographic limit in central Wisconsin. From this sample, and earlier work (1965–67) in northern Wisconsin, we estimated a number of demographic parameters. Snowshoe densities declined in both regions during the study years. There were 37 adults per 100 ha in central Wisconsin (summer 1980), and a maximum of 206 per 100 ha in the north (summer 1965). Sex ratios did not differ from 50:50. Adults comprised about 50% of fall and winter populations during each decline. Mean dates of first-litter conceptions were 20 March 1980 and 4 March 1981 in central Wisconsin, but much later (9 April 1965) in northern Wisconsin. Potential natality was higher in central than in northern Wisconsin, i.e., 10.8 versus 6.4 young per adult female; and higher too than reported elsewhere in the Great Lakes Region. This was due to a sustained high rate of pregnancy, and the occurrence of a fourth litter group. It is thus unlikely that either the abundance of snowshoe hares or their southern geographic limit in central Wisconsin is being determined by factors tending to depress reproduction. Annual adult and juvenile (first-year) survival were estimated at 0.22 and 0.11, respectively, in central Wisconsin (1980–81), and 0.31 and 0.07 in northern Wisconsin (1965–66). These rates are similar to those reported during population declines elsewhere.