Lb. Keith et Sem. Bloomer, DIFFERENTIAL MORTALITY OF SYMPATRIC SNOWSHOE HARES AND COTTONTAIL RABBITS IN CENTRAL WISCONSIN, Canadian journal of zoology, 71(8), 1993, pp. 1694-1697
During 1990 and 1991 we livetrapped and radio-collared cottontail rabb
its (Sylvilagus floridanus) and snowshoe hares (Lepus americanus) on f
ive sites (three in lowland deciduous cover, two in conifer bogs) in c
entral Wisconsin. The survival rates of these sympatric cottontails an
d snowshoes were equally high during snow-free periods from mid-March
through October. With the onset of persistent snow cover (mean depth 2
0 cm) and low temperatures (mean daily minimum -14-degrees-C) in Novem
ber 1991, the 60-day survival rate of cottontails plummeted from 0.89
to 0.18 (P < 0.01) whereas snowshoe survival declined only moderately
from 0.84 to 0.63 (P = 0.19). This interspecific difference reflected
continued high survival of snowshoes (0.80), but not of cottontails (0
.15), in the conifer bogs. Predation, primarily by coyotes, was the pr
oximate cause of 37 of 39 rabbit and hare deaths, and was thus the ove
rwhelming determinant of survival. We speculate that where persistent
snow and low temperatures characterize winter, the cottontail's greate
r foot loading, brown coloration, and escape behavior markedly increas
e its vulnerability to predators. This probably explains the absence o
f cottontails from the forests of northern Wisconsin.