188 BLACK BEAR DEN PHOTOGRAPHY American black bear denning behavior: observations and applications using remote photography Andrew S. Bridges, Josephine A. Fox, Colleen Olfenbuttel, and Michael R. Vaughan Abstract Researchers examining American black bear (Ursus americanus) denning behavior have relied primarily on den-site visitation and radiotelemetry to gather data. Repeated den-site visits are time-intensive and may disturb denning bears, possibly causing den abandon- ment, whereas radiotelemetry is sufficient only to provide gross data on den emergence. We used remote cameras to examine black bear denning behavior in the Allegheny Mountains of western Virginia during March–May 2003. We deployed cameras at 10 den sites and used 137 pictures of black bears. Adult female black bears exhibited greater extra-den activity than we expected prior to final den emergence, which occurred between April 12 and May 6, 2003. Our technique provided more accurate den-emergence esti- mation than previously published methodologies. Additionally, we observed seldom-doc- umented behaviors associated with den exits and estimated cub age at den emergence. Remote cameras can provide unique insights into denning ecology, and we describe their potential application to reproductive, survival, and behavioral research. Key words activity, behavior, black bear, denning, emergence, remote camera, Ursus americanus, Virginia Winter dormancy or hibernation in mammals is a and no formal techniques for examining and quanti- behavioral and physiological adaptation allowing fying behavioral characteristics have been described. these endothermic animals to survive periods of low Recently, remote cameras have become popular food availability and inclement weather (Smith and tools among wildlife biologists (Cutler and Swann Smith 2001). In American black bears (Ursus ameri- 1999). Researchers studying bears have used remote canus),winter dens serve not only as hibernacula but cameras to obtain population estimates (Mace et al. also as parturition chambers and nurseries (Nelson et 1994, Bowman et al. 1996, Martorello et al. 2001) and al. 1983, Hellgren 1998). Whereas researchers have examine activity patterns (Garshelis et al. 1993). thoroughly documented some aspects of black bear However, applications of remote cameras to study denning ecology such as site selection (Hellgren and denning behavior have not been described. Our Vaughan 1989, Schooley et al. 1994, Doan-Crider and objectives were to 1) examine black bear denning Hellgren 1996, Kasbohm et al. 1996) and reproduc- behavior using remote cameras, 2) describe a tech- tion (Clark and Smith 1994,Garshelis 1994,McLaugh- nique for deploying remote cameras at den sites, and lin et al. 1994, Noyce and Garshelis 1994), relatively 3) outline potential applications for this technique in little is known about behavior of bears while denning future research. Address for Andrew S. Bridges, Josephine A. Fox, and Colleen Olfenbuttel: Department of Fisheries and Wildlife Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0321, USA; e-mail for Bridges: [email protected]. Address for Michael R. Vaughan: U.S. Geological Survey, Virginia Cooperative Fish and Wildlife Research Unit, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0321, USA. Wildlife Society Bulletin 2004, 32(1):188–193 Peer refereed Black bear den photography • Bridges et al. 189 Study area infrared-triggered DeerCam® (Non Typical, Inc., Park Falls,Wisc.) cameras in our study. These cam- We conducted our study in Rockingham and eras documented date and time of activity with a Augusta counties, Virginia, on the George stamp on each photograph. We programmed units Washington and Jefferson national forests, part of for delays ranging from 1–30 minutes between the Allegheny Mountain Chain. Elevation ranged photographs and adaptively modified these set- from approximately 480–1,360 m (Kozak 1970). tings during deployment based on rate of film Forest cover types included eastern hemlock expenditure. We used 24- and 36-exposure 400ASA (Tsuga canadensis), sugar maple–beech–yellow film. birch (Acer saccharum, Fagus grandifolia, Betula We positioned cameras placed at tree dens based alleghaniensis), chestnut oak (Quercus prinus), on direction of tree lean, surrounding topography, pitch pine (Pinus rigida), white oak–black and location of bear claw marks on the tree. At oak–northern red oak (Q. alba, Q. velutina, Q. ground dens we positioned cameras based on rubra), northern red oak, yellow poplar entrance location and direction,surrounding topog- (Liriodendron tulipifera)–white oak–northern red oak,eastern white pine (P.strobus),mountain laurel raphy, and density of surrounding vegetation. We (Kalmia latifolia), and scrub oak (Q. ilicifolia; attached and secured cameras to trees with the Rawinski et al. 1994). locking cable and shoestring-cinch system included from the manufacturer. We used small (approxi- mately 10–30-cm-dbh) trees located 1.5–5 m from Methods and facing the expected location of emergence (Figure 1). We visited den sites to inspect cameras Bear handling and den location every 7–21 days or until the bear permanently We captured bears with Aldrich spring-loaded emerged from the den. foot snares and culvert traps from late May through late August 2002 (Johnson and Pelton 1980b). Cap- tured bears were sedated with a mixture of keta- mine hydrochloride and xylazine hydrochloride (200:100 mg/ml; 1 ml/45 kg; White et al. 1996) and equipped with radiotrans- mitters (ear tags or col- lars). Additionally, we weighed and measured each bear, determined sex and reproductive status, and removed a premolar for aging (Willey 1974). In December 2002 and January 2003, we used radiotelemetry to locate X bear dens. We returned to and entered (Godfrey et al. 2000) these dens in March 2003 to gather reproductive data and deploy remote cameras. Figure 1. Cameras deployed at tree dens should be placed approximately 2–4 m (solid line; depending on camera and sensor type) from the base of the tree. The bear will likely descend Camera deployment (dotted line) from the upward-facing slope of the tree; thus, aligning the camera with the flat area We used passive near its base (“X”) will maximize opportunity to document emergence behavior and litter size. 190 Wildlife Society Bulletin 2004, 32(1):188–193 Analyses relatively consistent, with 72.2% of activity bouts We developed film from each camera to deter- and starting times for final emergence occurring in mine whether the camera was deployed and func- the afternoon and early evening between 1300 and tioned properly. Based on our observations, we 2100 hours. defined an activity bout as a period of time during which the bear emerged from and subsequently reentered the den, where it remained for >3 hours. Discussion Final den emergence was defined as the series of Denning behavior photographs during which the bear did not reside Denning behavior in bears is difficult to record. in the den for >3 hours and did not return to the Prior to the recent development of automated data- den site. For each individual den, we noted time of recording devices such as remote cameras, only activity bouts, length of time spent during each direct observational methods and motion-sensitive bout, length of time between bouts, date of final transmitters were available to examine denning emergence, time of final emergence, total duration behavior. Direct observational methods (Matson of time spent at den site during final emergence, 1954) are time-intensive and may disturb denning and presence and number of cubs. For dens where bears, whereas motion-sensitive transmitters cubs were handled in March, we estimated birth (Johnson and Pelton 1979) offer only observations date using a regression model employing hair and of frequency of head movement. ear length (Bridges et al. 2002). High levels of extra-den activity exhibited by adult females prior to final emergence have not been reported in the scientific literature. We have Results observed that solitary bears may occasionally and We deployed cameras at 8 tree dens and 2 exca- temporarily leave their dens during periods of vation dens between March 17 and April 5, 2003. warm weather. However, the almost daily activity Due to equipment failure, 2 cameras placed at tree bouts of adult females with cubs were unexpected. dens failed to document activity or den emergence. Likewise, we have indirectly observed females car- At the remaining 8 den sites, we recorded 137 pho- rying cubs from den sites based on den relocation tographs documenting 42 activity bouts and final of females and their litters of pre-ambulatory cubs. emergence events. Cubs were present and docu- However, our photographs (Figure 2a) are among mented in photographs at all 8 dens. At tree dens the first direct documentations of this behavior in we photographed cubs outside the den only during wild black bears. Other previously undocumented final family-group emergence. In 4 of 6 dens where behaviors included adult females descending trees litter sizes were known (based on March handling), headfirst and eating snow (Figures 2b,c). Using a we observed the known number of cubs in our cub age-estimation technique (Bridges et al. 2002) photographs. In the remaining 2 instances,a female in conjunction with den-site cameras to record disturbed 1 camera during family-group emergence emergence allowed us to accurately quantify the and a nearby tree fell after the second camera’s parturition–emergence