Interaction of Snowshoe Hares and Woody Vegetation

Abstract

Winter feeding experiments with captive snowshoe hares (Lepus americanus) indicated a mean daily requirement of about 300 g of woody browse having a maximum diameter of 3-4 mm. Food supplies were measured near Rochester, Alberta, during 6 consecutive winters, (1970-71 to 1975-76). Food was insufficient for hare populations on 2 study areas during a cyclic peak (winter 1970-71) and the following winter; food was still in short supply on a 3rd study area 2 winters after the peak. Twenty hare exclosures and their control plots, established in 1968 and sampled in summer 1971 and 1972, showed that hares had reduced the total biomass of woody stems ≤1.5 cm in diameter by more than 50%. Browsing-intensity surveys conducted in 1971, at the end of the peak winter, disclosed that almost 50% of the woody stems had been severely or heavily browsed; 2 years later, less than 2% were so intensively browsed. Marked changes occurred in nutrient levels of 6 common browse species monitored during 1969-74, but these appeared unrelated in any causal way to changes in hare population parameters. Mortality of malnourished captive hares was significantly related to ambient winter temperatures. Results of these field observations and feeding trials are discussed in relation to the hypothesis that cyclic declines of snowshoe hare populations are initiated by overwinter food shortage.