Spring and Summer Habitat use and Food Habits of Black Bears in Northern Wisconsin
Storlid, Scott A.
University of Wisconsin-Stevens Point, College of Natural Resources
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In 1989 and 1990, I studied black bear (Ursus americanus) home range characteristics, productivity, density, spring and summer habitat use and food habits; and the role of black bears in white-tailed deer (Odocoileus virginianus) fawns mortality in northern Wisconsin. Seventeen (4 F, 13 M) and 19 (7 F, 12 M) radio-collared bears were located 1,165 times in 1989 and 1990, respectively. Bear hunters harvested 4 of 21 and 4 of 25 marked bears in 1989 and 1990, respectively. All bears harvested were boars. Four presumably ingressing males (1 yearling; 2 2-year-olds; 1 3-year-old) were captured on the study area the summer following the 1989 hunting season. Bears were most active between 0430 and 2230 hours CST, daily. Bears exhibited crepuscular peaks in activity being most active between 0500-0800 and 1700- 2000 hours, daily. Sow home range averaged 20.8 km^2• Boars were not tracked to the extent of their range, so their home range was not reported. Sows displayed overlapping home ranges but avoided each other through different temporal use patterns of the shared areas. I observed late summer and fall foraging movements outside established home range in only one of seven radio-collared females. Black bear density, excluding cubs and calculated in 1990, was 1 bear/2.76 km^2. Productivity and survivorship were determined by observing family groups and visiting bear dens. Sows produced cubs every other year and averaged 2.5 cubs/litter. Apparent first time breeders had fewer cubs (x = 2.25 cubs/litter, SD = 0.957, n = 4) than older sows (x = 3 cubs/litter, SD = 0.632, n = 6). Cub weights averaged 2.3 and 2.0 kg for females and males, respectively, and the observed sex ratio was 17M:7F. Survival from cub to yearling age class was 67% and appeared to be affected by the age and weight of the mother. Yearling weights averaged 22.0 and 23.7 kg for males and females, respectively. Food habits were determined by examining 97 bear scats. Grasses (Graminae), and sedges (Cyperaceae) were the most important prebreeding season foods; grasses, sedge, and soft mast including serviceberry (Amelanchier spp.) and wild sarsaparilla (Aralia nudicaulis) were important breeding season foods; and wild sarsaparilla, serviceberry, blackberry and raspberry (Rubus spp.), and insects, primarily ants (Formicidae ), were the most important foraging season foods. Plant material were more abundant in scats than animal material. However, white-tailed deer fawn remains were observed in 13% of scats during the breeding season. Important bear foods were present in all cover types except agricultural field. Use of cover types, however, appears to favor those with a midrange density shrub layer that limits horizontal visibility but does not impede bear movement. Females preferred lowland hardwoods, dominated by black ash (Fraxinus nigra), and avoided northern hardwoods, dominated by sugar maple (Acer saccharum ), throughout the year. Females and males selected aspen/hardwoods, dominated by trembling aspen (Populus tremuloides) with sugar maple subdominat, during the breeding season. Males avoided northern hardwoods during the breeding season and exhibited little other cover type preference. Open understory cover types (northern hardwoods) and open cover types (openings, open bog, agricultural field) were not selected. At the other extreme, densely vegetated cover types (aspen, some upland conifer), which may impede bear movement, were also not selected. Predation was studied by simultaneously monitoring marked bears and fawns. Nine fawns (4 F, 5 M) were monitored in 1989, and 14 fawns (7 F, 7 M) were monitored in 1990. Three male fawns were killed by unknown predators in 1989. Black bears killed 2 male fawns in late May and mid-June and an additional female fawn was missing after mid-July in 1990. Based on the black bear density, productivity, home range size, limited use of garbage, and lack of fall foraging movements, habitat quality on my study area is good to excellent. Management considerations for black bears in northern Wisconsin should concentrate on one goal - the preservation of the current mosaic of forest cover types in large enough blocks to allow for population viability. Humans appear to be the limiting factor of bears in northern Wisconsin. Management of human attitudes regarding bear densities through education should guarantee a productive bear population in the future.