Editor’s Note: This review updates research since our last Bibliography Notes on this topic, in May/June 1998 (Vol. 3 #3, or visit: http://www.wildlandscpr.org/biblio-notes/roads-kill-grizzly-bears-and-ef... [1]). Since that time, more research has addressed the effects of highways and railroads, rather than just low volume roads.

It has long been understood that roads have detrimental effects on bears and bear populations (both black and grizzly bears; see The Road Riporter Vol. 3 #3). As humans continue to develop bear habitat, construct more roads, and increase traffic volume on existing roads, we are reducing and fragmenting bear habitat. In addition, bear habitat that is protected from human development is increasingly used for recreation, reducing the amount of secure habitat for bears even where roads are limited. The primary factors associated with roads that affect bears are habitat loss and fragmentation, direct traffic-related and railroad mortality, habituation to humans and food-conditioning, and increased susceptibility to hunting and poaching due to better access for humans and loss of wariness in bears. Increased awareness of the negative effects of roads on bear habitat has compelled some agencies to close and decommission roads to improve bear habitat. In this article, I review recent research on the impacts of roads and other linear barriers on bears and propose ways to mitigate these impacts.

Habitat Loss and Fragmentation
The impacts of habitat loss and fragmentation have received increased research attention over the past decade. On Alaska’s Kenai Peninsula, rapid human development is moving toward isolating the brown bear population from populations further inland. Traffic mortality, barrier effects from the Sterling Highway, increased rates of bears killed in defense of life or property, and a lack of genetic influx may soon threaten the population if human development is not checked (Suring and Del Frate 2005; Graves et al. 2006). On the Bow River watershed in Alberta, Chruzscz, et al (2003) found that the cumulative effects of human use, development, and railroads have limited grizzly bear access to important habitats and may negatively impact the bears’ populations.

There are variations in bears’ use/avoidance of different roads depending on the type and amount of human use (Peralvo et al. 2005). For example, Reynolds-Hogland and Mitchell (2007) found that black bears in protected sanctuaries in the southern Appalachians reacted differently to paved and gravel roads depending on their previous experience with each type of road. In the Pisgah Bear Sanctuary in North Carolina, hunting and poaching in the area surrounding the sanctuary posed more of a mortality risk than did vehicle collision (Reynolds-Hogland and Mitchell 2007). They speculated that the bears associated gravel roads with hunters and poachers, while the paved roads posed less of a risk.

Direct Mortality from Vehicle Collisions and Railroads
Collisions with vehicles has been a well documented source of mortality for bears (e.g., Gibeau and Herrero 1998; Forman and Alexander 1998; Kaczensky et al. 2003). In addition to highway mortality, railroads can pose an equal or larger threat to bears than do traditional roads (Waller and Servheen 2005; Huber et al. 1998; Kaczensky et al. 2003). In Montana, a railroad caused more direct mortality than the adjacent Highway 2, because bears attempted to cross the transportation corridor at night when highway traffic was lowest. However, in many cases, the railroad saw more traffic at night, and the bears would cross the highway successfully only to be hit by a train (Waller and Servheen 2005). Additionally, bears often use the railroad as a movement corridor (Kaczensky et al. 2003), and grain spills act as a further attractant (Waller and Servheen 2005).

Habituation and Conditioning
Loss of wary behavior in bears is a significant and complicated effect of roads. Additionally, high levels of human access present different problems depending on unique sets of conditions. When bears are exposed to humans over a period of time their response to humans changes depending on their cumulative experience (Herrero et al. 2005). If exposure has neutral consequences, they often become “human-habituated,” meaning that they become accustomed to human presence, and “they conserve energy by muting their reaction” (Herrero et al. 2005). When exposure to humans results in food rewards, bears become “food-conditioned,” meaning that they come to associate humans with an easy meal, whether it be from humans actively feeding bears, or if the bear learns to raid campsites and picnic sites or steal fish from anglers. Food-conditioning is probably the most problematic result of exposure to humans, as bears conditioned to human foods are more likely to become aggressive towards humans, and even occasionally treat humans as prey (Herrero 2002).

Poaching and Defense of Life and Property
Habituation to humans makes unprotected bears more susceptible to the dangers of interactions with humans, and even protected bears become more vulnerable to poaching or to legal harvest when they leave protected areas. A study of known grizzly bear mortality in and around Banff and Yoho National Parks showed that all human-caused mortalities in the study area between 1971 and 1998 occurred in areas along roads, trails, or around human settlements (Benn and Herrero 2002). Outside protected areas, Wielgus et al. (2002) recommended that open roads in grizzly bear habitat should be restricted to forestry use only.

Defense of life and property (DLP) can also be a significant source of bear mortality. Suring and Del Frate (2002) found that the number of brown bears killed due to DLP on the Kenai Peninsula increased with road density, especially when roads occur near or increase access to favorable habitat such as salmon-bearing streams. They recommend that any new or upgraded recreational sites should be concentrated “as far as possible from salmon streams” (Suring and Del Frate 2002). However, this may be problematic, because salmon fishing is one of the area’s most popular recreational activities.

Possible Mitigation Strategies
While the effects of roads on bears are multiple and widespread, there are strategies to mitigate these effects. Some of the more viable options include establishing connectivity between areas of high quality bear habitat (Servheen et al. 2001; Primm and Wilson 2004), highway crossing structures and fencing (Jaeger and Fahrig 2003), road closure and decommissioning (Switalski et al. 2007), control of human development (Gibeau et al. 2001), temporal closures (Graves et al. 2006), installation of wildlife sensors (Gordon et al. 2004), aversive conditioning (http://www.beardogs.org [2]), and removal of bear attractants from roadsides and areas of human development (Weaver 2004). All of these strategies must examine the specific needs of each area, as successful mitigation strategies will differ with each situation (Clevenger and Waltho 2000; Clevenger et al. 2002).

Conclusion
“In the end, the most difficult aspect of making real gains in grizzly bear conservation may be mustering the social and political will to implement change” (Gibeau et al. 2001). Humans have had an enormous impact on bears all over the world, and as human population and development increases, bears continue to lose more habitat. If bears are to persist, humans are going to have to make some changes and learn to coexist with bears and other wildlife. Effective strategies for bear conservation exist, but we must implement and enforce them. Bear conservation will involve setting aside areas with restricted or controlled human use and access, controlling human development and road construction in bear habitat, and educating people to better understand bears, their behavior, and their habitat requirements.

— Shannon Donahue is a University of Montana Environmental Studies graduate student and has previously worked to help mitigate bear-human conflicts.

References

Benn B. and S. Herrero. 2002. Grizzly bear mortality and human access in Banff and Yoho National Parks, 1971–1998. Ursus. 13:213–221.

Chruzscz, B., A.P. Clevenger, K.C. Gunson, M.L. Gibeau, B.Chruzscz. 2003. Relationships among grizzly bears, highways, and habitat in the Banff-Bow valley, Alberta, Canada. Canadian Journal of Zoology. 81(8):1378-91.

Clevenger, A.P. and N. Waltho. 2000. Factors influencing the effectiveness of wildlife underpasses in Banff National Park, Alberta, Canada. Conservation Biology 14:47-56.

Clevenger, A.P., J. Wierzchowski, B. Chruszcz, K. Gunson. 2002. GIS-generated, expert- based models for identifying wildlife habitat linkages and planning mitigation passages. Conservation Biology 16(2):503-514.

Forman, R.T.T. and L.E. Alexander. 1998. Roads and their major ecological effects. Annual Review of Ecology and Systematics. 29:207-231+C2.

Gibeau, M.L., S. Herrero. 1998. Roads, rails and grizzly bears in the Bow River Valley, Alberta. In: Evink, G., Ziegler, D., Garrett, P. Berry, J. (Eds.), Proceedings of the International Conference on Wildlife Ecology and Transportation, Publication FL-ER-69-98. Florida Department of Transportation, Tallahassee, USA, pp. 104–108.

Gibeau M.L., S. Herrero, B.N. McLellan, J.G. Woods. 2001. Managing for grizzly bear security areas in Banff National Park and the central Canadian Rocky Mountains. Ursus. 12:121-129.

Gordon, K.M., M.C. McKinstry, S.H. Anderson. 2004. Motorist response to a deer-sensing warning system. Wildlife Society Bulletin. 32(2):565-573.

Graves, T.A, S. Farley, C. Servheen. 2006. Frequency and distribution of highway crossings by Kenai Peninsula brown bears. Wildlife Society Bulletin. 34(3):800-8.

Herrero, S. 2002. Bear Attacks: Their Causes and Avoidance. Revised Edition. The Lyons Press, Guilford, Connecticut, USA.

Herrero, S., T. Smith, T.D. DeBruyn, K. Gunther, C. Matt. 2005. From the field: Brown bear habituation to people – safety, risks, and benefits. Wildlife Society Bulletin. 33(1):362-373.

Huber, D., J. Kusak, A. Frkovic. 1998. Traffic kills of brown bears in Gorski Kotar, Croatia. Ursus. 10:167-171.

Interagency Conservation Strategy Team. 2007. Final Conservation Strategy for the Grizzly Bear in the Greater Yellowstone Area. http://www.fws.gov/mountain-prairie/species/mammals/grizzly/Final_Conservation_Strategy.pdf [3]

Jaeger, J.A.G. and L. Fahrig. 2003. Effect of road fencing on population persistence. Conservation Biology. 18(6):1651-1657.

Kaczensky, P., F. Knauer, B. Krze, M. Jonozovic, M. Adamic, H. Gossow. 2003. The impact of high speed, high volume traffic axes on brown bears in Slovenia. Biological Conservation. 111:191-204.

Peralvo, M.F., F. Cuesta, F. van Manen. Delineating priority habitat areas for the conservation of Andean bears in northern Ecuador. 2005. Ursus.16(2):222-233.
Reynolds-Hogland, M.J., M.S. Mitchell. 2007. Effects of roads on habitat quality for bears in the Southern Appalachians: A Long-Term Study. Journal of Mammalogy. 88(4):1050-61.

Servheen, C., J.S. Waller, P. Sandstrom. 2001. Identification and management of linkage zones for grizzly bears between the large blocks of public land in the northern Rocky Mountains. U.S. Fish and Wildlife Service.
Suring L.H. and G. Del Frate. 2002. Spatial analysis of locations of brown bears killed in defense of life or property on the Kenai Peninsula, Alaska, USA. Ursus. 13:237-245.

Switalski, T Adam, Len Broberg, and Anna Holden. 2007. Wildlife use on open and decommissioned roads on the Clearwater National Forest, ID. In: Proceedings of the International Conference on Ecology and Transportation, edited by CL Irwin, P Garrett, and KP McDermott. Raleigh, NC: Center for Transportation and the Environment, North Carolina University. 627-632.

Waller, J.S. and C. Servheen. 2005. Effects of transportation infrastructure on grizzly bears in northwestern Montana. Journal of Wildlife Management. 69(3):985-1000.

Weaver, H.W. 2004. Biometric analysis and aversive conditioning of black bears in southern West Virginia. Thesis,Wildlife and Fisheries Resource Management Program, Davis College of Agriculture, Forestry, and Consumer Sciences at West Virginia University.

Wielgus R.B., P. Vernier, T. Schivatcheva. 2002. Grizzly bear use of open, closed, and restricted forestry roads. Canadian Journal of Forest Research. 32(9):1597-1606.