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188 BLACK DEN PHOTOGRAPHY denning behavior: observations and applications using remote photography

Andrew S. Bridges, Josephine A. , Colleen Olfenbuttel, and Michael R. Vaughan

Abstract Researchers examining American black bear ( 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 , 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 of western 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 in is a and no formal techniques for examining and quanti- behavioral and physiological adaptation allowing fying behavioral characteristics have been described. these endothermic 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 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 and Jefferson national , 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 cover types included eastern hemlock expenditure. We used 24- and 36-exposure 400ASA ( canadensis), sugar ––yellow film. (Acer saccharum, Fagus grandifolia, Betula We positioned cameras placed at dens based alleghaniensis), (Quercus prinus), on direction of tree lean, surrounding topography, pitch (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 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 (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 interval for the first time in deployment and partially obstructed our view of wild black bears. the den tree. For all 8 dens, we successfully docu- In previous studies den emergence dates were mented final emergence time and date. Six litters estimated based on consecutive radiotelemetry of cubs emerged between 77–93 days of age (x-=83 locations (Johnson and Pelton 1980a, Tietje and days). We photographed 3 adult females carrying Ruff 1980). Researchers used the midpoint of the cubs from the dens in their mouths. In 7 of 8 dens, last triangulation near the den site and the first tri- duration of final emergence events ranged from angulation substantially removed from the den site 42–259 minutes; in the remaining instance the fam- as the date of den emergence (Hellgren and ily group remained near the base of the tree for Vaughan 1989, Seibert 1995, Oli et al. 1997). This approximately 24 hours. We documented activity method results in low precision in emergence-date bouts for all 8 adult females during which they tem- estimation due to limited numbers or triangulations porarily departed from and subsequently returned and error inherent in telemetry-based locations. to their den prior to final family-group emergence. Additionally, bears may remain in the general vicin- Although length of time spent during and between ity of their den for 10–12 days after emergence activity bouts was variable, timing of activity was (Hellgren and Vaughan 1989), resulting in post- Black bear den photography • Bridges et al. 191

a gence estimation; however, this method is time-intensive and retains error inherent to use of a midpoint based on observations separated by several days. Remote cameras offered nearly error-free quantifica- tion of both date and time of emer- gence and required relatively little researcher time and effort. Remote cameras may not be appropriate for all situations. Monetary cost of purchasing cam- eras and supplies may be prohibi- tive to limited research budgets. Additionally,inclement weather may b limit access to dens, and researcher presence at open den sites (e.g., ground nests) may disturb denning bears. Camera deployment recommendations Direct observation of bears and bear claw marks on tree trunks indi- cate the bears consistently climb a particular side of a tree. Leaning trees are generally climbed on the skyward (upward-facing) side. In mountainous terrain trees tend to c lean downhill and bears accordingly tend to climb on the uphill side (Figure 1). We found that 2–4 m was the optimal distance from camera to target. Cameras <2 m from dens did not offer adequate field of view to fully document behavior and repro- duction and frequently were dis- turbed by the bears. At distances >4 m the passive heat sensors in our cameras were not always reliable in detecting the presence of the adult. Optimal deployment distances may vary if different types of triggers (e.g., active infrared) are employed. Because of the high levels of extra- Figure 2. Use of remote cameras at den sites allowed us to document rarely observed behaviors including a) a sow carrying a cub from the den in its mouth, den activity prior to final emer- b) bear descending a tree headfirst, and c) bear consuming snow. The date and gence and duration of time spent time stamps (visible in the lower right corner of photographs “a” and “c”) provid- near the den during emergence, we ed date and time of den-emergence activity. recommend 36-exposure rolls of film for traditional cameras or high- emergence den-site triangulations and late-bias capacity memory cards for digital cameras. estimates. Hiking to den sites can improve emer- Because we found that bears may disturb cameras, 192 Wildlife Society Bulletin 2004, 32(1):188–193 and to insure adequate film supply in the event of Acknowledgments. Primary funding for our high extra-den activity, we recommend that cam- research was provided by the Virginia Department eras be checked at <7-day intervals. The delay of Game and Inland Fisheries (VDGIF) through the between photographs should be set based on den Federal Aid in Wildlife Restoration Project WE-99-R, type,reproductive status,frequency with which the Virginia Polytechnic Institute and State University, researcher can visit the site to replenish film, and the Virginia Cooperative Fish and Wildlife Research study objectives. We found that delays ranging from Unit, and the United States Forest Service. 5–30 minutes were effective in different circum- Additional support was provided by stances, with shorter delays offering more com- Pacific, National Fish and Wildlife Foundation, plete documentation and longer delays better con- National Geographic Society,Northern Shenandoah serving film. Audubon Society, Safari Club International, Union Camp Corporation, United States Forest Service, Suggestions for future applications Virginia Bear Hunters Association, the Virginia For situations in which entering dens is unsafe for Department of Transportation,Virginia Houndsmen the researchers (e.g., grizzly bears [Ursus arctos]) and Sporting Association, Virginia Chapter of or where bears cannot be handled in their dens, a the Sierra Club, Virginia Wilderness Committee, remote camera placed outside the den structure can Wildlife Forever Foundation, and Westvaco. provide an estimate of cub production. We were We thank M. Chamberlain, D. Steffen, F. van able to document reproductive status (e.g., with Manen, and one anonymous reviewer for their cubs) for all 8 adult bears photographed. many constructive suggestions, and our 2003 den Additionally, in all 4 instances in which litter size crew (A. Bourgeois, D. Kocka, D. Martin, J. McKay,R. was known and the camera was not disturbed or Propst., J. Ransom, and J. Smith) for their assistance obstructed, we were able to accurately quantify in the field. The Virginia Polytechnic Institute and reproductive output based on photographs. If bears State University’s Care and Use Committee are handled in the den and cameras deployed at the approved animal handling protocols. den site are not disturbed, minimum cub-survival estimates could be obtained based on number of cubs handled during den work and subsequently Literature cited photographed during den emergence. Marking BOWMAN,J.L.,M.J.CHAMBERLAIN,B.D.LEOPOLD, AND H. A. JACOBSON. 1996. An evaluation of two censusing techniques to estimate cubs with individual-specific visibly identifiable black bear population size on White River National Wildlife markers similar to those employed in mark–resight Refuge, Arkansas. Proceedings of the Annual Conference of population estimation studies (Mace et al. 1994, the Southeastern Association of Fish and Wildlife Agencies 50: Bowman et al. 1996, Martorello et al. 2001) would 614–621. allow for individual identification and improve sur- BRIDGES, A. S., C. OLFENBUTTEL, AND M. R. VAUGHAN. 2002. A mixed regression model to estimate neonatal black bear cub age. vival estimates. Additionally, researchers could gain Wildlife Society Bulletin 30:1253–1258. insight into timing and possibly causation of aban- CLARK,J.D.,AND K. G. SMITH. 1994. A demographic comparison of donments (Hellgren and Vaughan 1989, Godfrey et two black bear populations in the Interior Highlands of al. 2000) subsequent to den handling. Arkansas. Wildlife Society Bulletin 22:593–603. Recently,remotely triggered digital still and video CUTLER,T.L.,AND D. E. SWANN. 1999. Using remote photography in wildlife ecology: a review. Wildlife Society Bulletin 27: cameras have become available. Digital still cam- 571–581. eras offer high-capacity memory cards that can DOAN-CRIDER,D.L.,AND E. C. HELLGREN. 1996. Population charac- store larger numbers of images than the traditional teristics and winter ecology of black bears in , Mexi- film cameras used in our research. Digital video co. Journal of Wildlife Management 60:398–407. cameras will offer further insights into behavior of GARSHELIS,D.L. 1994. Density-dependent population regulation in black bears. International Conference on Bear Research and bears during pre-emergence activity bouts as well Management Monographs 3:3–14. as during final emergence and might help elucidate GARSHELIS, D. L., P.L. COY, AND B. D. KONTIO. 1993. Applications of whether extra-den exercise plays a role in muscle remote animal-activated cameras in bear research. Proceed- strength retention during periods of seeming inac- ings of the International Union of Biologists 21: tivity (Harlow et al. 2001). Additionally, video 315–322. GODFREY,C.L.,K.NEEDHAM,M.R.VAUGHAN,J.H.VASHON,D.D.MARTIN, recordings will allow researchers to better view AND G. T. BLANK. 2000. A technique for and risks associated and count cubs and thereby improve accuracy of with entering tree dens used by black bears. Wildlife Society reproductive and survival estimates. Bulletin 28:131–140. Black bear den photography • Bridges et al. 193

HARLOW,H.J.,T.LOHUIS,T.D.I.BECK, AND P. A . I AIZZO. 2001. Muscle WHITE,T.H., JR., M. K. OLI,B.D.LEOPOLD,H.A.JACOBSON,AND J.W. KAS- strength in overwintering bears. Nature 409:997. BOHM. 1996. Field evaluation of Telazol® and ketamine- HELLGREN, E. C. 1998. of hibernation in bears. Ursus xylazine for immobilizing black bears. Wildlife Society Bulletin 10:467–477. 24:521–527. HELLGREN,E.C.,AND M.R.VAUGHAN. 1989. Denning ecology of black WILLEY, C. 1974. Aging black bears from first premolar tooth sec- bears in a southeastern wetland. Journal of Wildlife Manage- tions. Journal of Wildlife Management 38:97–100. ment 53:347–353. JOHNSON,K.G.,AND M. R. PELTON. 1979. Denning behavior of black bears in the National Park. Proceed- ings of the Annual Conference of the Southeastern Association of Fish and Wildlife Agencies 33:239–249. JOHNSON,K.G.,AND M. R. PELTON. 1980a. Environmental relation- ships and the denning period of black bears in . Journal of Mammalogy 61:653–660. JOHNSON,K.G.,AND M. R. PELTON. 1980b. Prebaiting and snaring techniques for black bears. Wildlife Society Bulletin 8:46–54. KASBOHM,J.W.,M.R.VAUGHAN,AND J. G. KRAUS. 1996. Black bear den- ning during a gypsy moth infestation. Wildlife Society Bulletin 24:62–70. KOZAK, S. J. 1970. Geology of Elliot Knob, Deerfield, Craigsville, and Augusta Springs quadrangles, Virginia. Virginia Depart- ment of Conservation and Recreation, Division of Natural Her- itage, Richmond, USA. MACE,R.D.,S.C.MINTA,T.L.MANLEY,AND K. E.AUNE. 1994. Estimat- ing population size using camera sightings. Wildlife Society Bulletin 22:74–83. MARTORELLO, D.A.,T. H. EASON, AND M. R. PELTON. 2001. A sighting technique using cameras to estimate population size of black bears. Wildlife Society Bulletin 29:560–567. MATSON, J. R. 1954. Observations on the dormant phase of a female black bear. Journal of Mammalogy 35:28–35. MCLAUGHLIN, C. R., G. J. J. MATULA, AND R. J. O’CONNOR. 1994. Syn- chronous reproduction by black bears. International Conference on Bear Research and Management 9:471–479. NELSON, R.A., G. E. J. FOLK,E.W.PFEIFFER,J.J.CRAIGHEAD,C.J.JONKEL, AND D. L. STEIGER. 1983. Behavior, biochemistry, and hiberna- tion in black,grizzly,and polar bears. International Conference on Bear Research and Management 5:284–290. NOYCE,K.V.,AND D. L. GARSHELIS. 1994. Body size and blood char- Andrew Bridges and Jodi Fox (first photo, left and right, respec- acteristics as indicators of condition and reproductive per- tively) conducted fieldwork together from 2000–2003 on the formance in black bears. International Conference on Bear Virginia Cooperative Allegheny Bear Study’s northwestern field Research and Management 9:481–496. site. Andrew received his B.S. from the University of , OLI, M. K., H.A. JACOBSON,AND B. D. LEOPOLD. 1997. Denning ecolo- his M.S. from A&M, and is currently finishing a Ph.D. at gy of black bears in the White River National Wildlife Refuge, Virginia Tech, where he is analyzing data from 10 of field- Arkansas. Journal of Wildlife Management 61:700–706. work in western Virginia. His interests include population and behavioral ecology as well as development and refinement of RAWINSKI,T.J.,G.P.FLEMING,AND F. V. J UDGE. 1994. Forest vegetation field techniques for terrestrial vertebrates. Jodi holds a B.A. of the Ramsey’s Draft and Little Laurel Run Research Natural from St. Louis University and is interested in mammalian ecol- Areas, Virginia: baseline ecological monitoring and classifica- ogy. Colleen Olfenbuttel (second photo, left) earned her B.S. tion. Virginia Department of Conservation and Recreation, from University, is currently pursuing an M.S. at Virginia Division of Natural Heritage, Richmond, Virginia, USA. Tech, and her interests include habitat ecology, predator–prey SCHOOLEY, R. L., C. R. MCLAUGHLIN,G.J.MATULA,JR., AND W. B . K ROHN. interactions, and wildlife– conflicts. Michael R. 1994. Denning chronology of female black bears: effects of Vaughan (second photo, right) holds a B.S. from food, weather, and reproduction. Journal of Mammalogy 75: State, an M.S. from State, and a Ph.D. from the 466–477. University of . Currently Assistant Leader of the Virginia Cooperative Fish and Wildlife Research Unit, his areas SEIBERT, S. G. 1995. Winter movements of denning black bears in of expertise include large- population dynamics and northwest Florida. Proceedings of the Annual Conference of predator–prey ecology. the Southeastern Association of Fish and Wildlife Agencies 49: 283–291. SMITH,R.L.,AND T. M. S MITH. 2001. Ecology and Field Biology. Ben- jamin Cummings, San Francisco, , USA. TIETJE,W.D.,AND R. L. RUFF. 1980. Denning behavior of black bears in boreal forest of . Journal of Wildlife Management 44: 858–870. Associate editor: Chamberlain