Selection and Availability of Dens for Black Bears in Tennessee

Abstract

Radiotelemetry data indicated that black bears (Ursus americanus) in the Great Smoky Mountains National Park, Tennessee, prefer tree cavities above ground as winter dens. Adult females and subadults of both sexes selected tree dens more frequently (P < 0.078) than did adult males. Because parturition and lactation occur in winter dens, secluded and well-insulated tree cavities, which provide better protection than ground dens, appear to enhance survival and reproduction. A greater proportion (P < 0.010) of adult females and a higher bear density were found in the primary tree-denning area of the Park. Analysis of vegetation showed no absolute shortage of tree dens; however, their clumped distribution due to logging before the Park was established resulted in tree dens being less available in certain watersheds and especially at low elevations. Site and vegetation differences at dens enabled classification, through discriminant function analysis, of areas with the highest potential availability of dens. Tree dens may afford the extra protection necessary to maintain bear populations within marginal habitats of the southern Appalachian Mountains. J. WILDL. MANAGE. 45(1):111-119 Black bears use a wide variety of sites for winter dens. The most common den types include excavated and natural depressions under tree roots, stumps, fallen logs (Erickson 1964:100, Lindzey and Meslow 1976), boulders (Jonkel and Cowan 1971:22, LeCount 1977), or inside the bases of hollow trees (Jonkel and Cowan 1971:22, Bromlei 1973:94). Occasionally bears den in unsheltered depressions (Erickson 1964:100, Hamilton and Marchinton 1977) or man-made structures such as drainage culverts (Barnes and Bray 1966) and under buildings (Jonkel and Cowan 1971:22). Use of radiotelemetry has resulted in reports of bears selecting tree cavities above ground as dens (Taylor 1971:67; Ernst, unpubl. rep., Ga. Fed. Aid Proj. W-37-R, 1972; Conley 1976; Lindzey and Meslow 1976; Hamilton and Marchinton 1977; Pelton et al. 1977). However, lack of information on the relative availability of different types of dens has precluded determination of preferences by bears among the types. The broad range of den types reported in the literature indicates that specific den requirements may not be important to the survival of black bears. However, most reports are from northern regions where snow plays an important role in concealment and insulation of denning bears. The natural sealing of entrances to ground dens by snow in Minnesota decreased the bears' winter energy requirements by 27% (Maxwell and Thorkelson, unpubl. rep., North Cent. For. Exp. Stn., 1975). Southern regions are generally free of snow cover but experience heavy winter rains. Hammel (1955) showed that moist pelts have 5-20% greater conductivity than dry pelts, and that small amounts of water vapor can produce this variation. Open ground dens also would result in greater heat loss due to air turbulence. Thorkelson and Maxwell (1974) found that an air turbulence of 150 cm/ second increased total heat loss of a raccoon (Procyon lotor) in an open den by 33%. Free-ranging dogs and human encroachment pose additional threats to southern bear populations. These factors plus frequent winter flooding (Landers et J. Wildl. Manage. 45(1):1981 111 This content downloaded from 157.55.39.253 on Wed, 08 Jun 2016 06:04:28 UTC All use subject to http://about.jstor.org/terms 112 BEAR DENS IN TENNESSEE * Johnson and Pelton