Date of Award
Master of Science
Wildlife and Fisheries Science
Michael R. Pelton
James T. Tanner, Boyd L. Dearden
Radiotelemetry was used to locate winter dens, determine the denning period, and gather observations on the denning behavior of black bears (Ursus americanus) in a 42,800 ha portion of the Great Smoky Mountains National Park (GSMNP). After spring emergence, dens and the site parameter were measured and the vegetation sampled. Random transects and factor and discriminant function analysis were used to determine the availability of dens and denning habitat.
The denning period averaged 94 days with most bears entering dens between the last week in December and the first week in January and emerging from dens between the last week in March and the first week in April. Adult females entered dens first, adult males next, and subadults of both sexes denned last. Emergence was in reverse sequence. Females with newborn cubs exited dens later (P < .002) and denned longer (P < .0107) than other females.
Weather, principally increased precipitation, and lower maximum and higher minimum daily temperatures, provided the proximate stimulus to den but food availability also apparently influenced entrance of bears into dens since bears denned earlier (P < .0004) in years (1972-1974) with a fair to poor mast yield than in years (1976-1978) with excellent mast yields. A circannual (endogenous) rhythm as the ultimate mechanism encompasses the observed variations in environmental factors affecting the denning period of bears over their broad geographic range and diverse ecological conditions.
Significant increases in inactivity occurred in the pre- and postdenning periods with the transition into and out of dormancy occurring gradually over a period of about one month. This may be a physiological transition period. The frequency of head movements increased (P < .005) prior to den emergence indicating movements within dens and readjustment to normal behavior.
Preferred den sites were cavities high above ground (x- = 11.15m) in large (x- dbh = 94.8 cm) yellow birches (Betula alleghaniensis), eastern hemlocks (Tsuga canadensis), red maples (Acer rubrum) and northern red oaks (Quercus rubra). The majority of ground dens (78%) were cavities under root systems of wind-tilted trees or in association with stumps. Dens generally occurred on steep slopes (x- = 33°) at high elevations (x- = 1104 m). This was probably related to the inaccessibility of these areas to pre-Park logging activities and the importance of wind damage to den formation.
Adult females and sub-adults of both sexes more often (P < .078) selected tree cavities above ground than did adult males. Tree dens offered seclusion from ground disturbances and superior energy conservation over ground dens and likely serve as important maternity denning areas and centers of dispersal. Population data from the watershed with the majority of active tree dens showed a higher concentration (P < .0102) of adult females and higher density than the study area wide population of wild bears. Tree dens may afford the extra protection necessary to maintain viable black bear populations in islands of dwindling and often marginal habitat.
Application of the Poisson distribution to 30 random transects (60 ha) yielded an estimate of 2140 ± 92 (two standard deviations) tree dens in the study area which has an estimated population of 129 bears (range 93 to 174, CI = 95%). However, the clumped distribution of tree dens results from the pre-Park logging history results in tree cavities being less available to bears in certain watersheds and especially at low elevations. Consequently, ground dens are more frequently selected (P < .005) and indications are that bear densities are generally lower in these areas. No use or reuse of potential and active tree dens further indicated an abundant supply of tree cavities available to bears in the virgin portions of the GSMNP. Ground dens were 4.7 times more abundant than tree dens.
Discrete differences of site and vegetation parameters at tree and ground dens enabled classification through discriminant function analysis of areas with the highest den potential. Preservation of tree den habitat, as well as the specific den sites, could then be incorporated into forest management outside the Park. A productive approach for the future would be to coordinate black bear sanctuary and wilderness establishment with areas identified as having high tree den potential.
Johnson, Kenneth Gregory, "Den Ecology of Black Bears (Ursus americanus) in the Great Smoky Mountains National Park. " Master's Thesis, University of Tennessee, 1978.