Population Ecology of Snowshoe Hares in the Central Rocky Mountains

Measurements of natality rates, survival rates, movements, and densities were integrated to describe the mechanics of population balance for snowshoe hares (Lepus americanus) in Colorado (1969-71) and Utah (1972-73), near the southern extreme of this species\u27 range. Adult home-range size averaged eight hectares in spruce (Picea spp.)-fir (Abies spp.) forest, the preferred habitat. Juveniles used unforested habitat more frequently than adults. Population density remained stable throughout the duration of both studies; historical accounts also indicate population densities have remained fairly stable in the Rocky Mountain region. Hares commenced breeding from mid-April to mid-May. Females surviving an entire reproductive season produced an average of 2.1-2.3 litters annually. Later-litter sizes, averaging 4.8 in Colorado and 5.9 in Utah, were larger than most litter sizes reported from higher latitudes. The annual natality rate was 8.2 and U.5 young per female surviving an entire reproductive season in Colorado and Utah, respectively. Annual survival rate for adults in Colorado was 0.45. About 16 percent of juveniles born each summer needed to survive until the follOwing breeding season to balance the population density. Second-litter juveniles had a lower survival rate than did first-litter juveniles. We surmise the long-term stability of the hare population in the Rocky Mountains to be related to dispersal of juveniles into poor (open) habitats where survival is low. The discontinuity of preferred spruce-fir habitat allows dispersal into open habitat to occur readily, and this may be the main mechanism averting the potential population increase