WildEarth Guardians works to protect and restore wildlife, wild places and wild rivers in the American West.

Off-Road Vehicle Impacts on Wildlife

Forests are home to hundreds of species of fish and wildlife, providing recreational opportunities for hunters, anglers, and wildlife enthusiasts.  Millions of hunters and fishermen enjoy pursuing their sport while increasing numbers of birders and photographers enjoy simply catching a glimpse of the diversity of forest life.  In addition to recreational benefits, diverse wildlife are a sign of overall ecosystem health and integrity.  While there are many threats to preserving wildlife ranging from global warming to development, the negative impacts from off-road vehicles (ORVs) on wildlife have been well documented in the scientific literature.  ORVs can impact wildlife through direct mortality, increased legal and illegal harvest, disturbance, and habitat loss.   

Direct Mortality

One of the most apparent impacts of ORVs on wildlife is collisions and direct mortality.  Direct impact will kill most species, but amphibians, reptiles, small mammals and ground nesting birds are most vulnerable (Wilkins 1982, Rei and Seitz 1990, Fahrig et al. 1995, Ashley and Robinson 1996, Gibbs 1998, DeMaynadier and Hunter 2000).  With millions of ORVs traversing the landscape at high speeds (up to 60 mph), the number of animals being killed can be significant.

Habitat Security

Several studies have found that large animals such as elk, wolves, and bears are negatively impacted by the loss of habitat security resulting from increased motorized access.  Depending on the species, some wildlife are more sensitive to disturbance during critical times of year, such as winter habitat for ungulates or areas important for grizzly bear food sources during spring (USDI 1987).  

Elk have been the most extensively studied animal in relation to motorized access.  While recent studies have made a direct connection between ORVs and impacts to elk (Vieira 2000, Wisdom et al. 2004, Wisdom 2007, Grigg 2007), most studies have looked more broadly at the impacts of motorized travel and roads on elk.  It can be assumed that these impacts would be similar on ORV routes.  Many studies have found that increased motorized access results in decreased elk habitat and security (Lyon 1983; Figure 3), and increased elk mortality from hunter harvest both legal and illegal (Hershey and Leege 1982, Hayes et al. 2002, McCorquodale et al. 2003, see Rowland et al. 2005 for review).  

Closing or decommissioning roads has been found to decrease hunter induced mortality (Leptich and Zager 1991), increase elk survivorship (Cole et al. 1997), increase the number of bulls (Leptich and Zager 1991), extend the age structure (Leptich and Zager 1991), increase hunter success (Gratson and Whitman 2000), and allow elk to remain in preferred habitat longer (Irwin and Peek 1979).  Studies have also recommended closing entire areas to motorized use— as opposed to individual roads— to best promote healthy elk populations (Hurley 1994, Burcham et al. 1998, Rowland et al. 2005).

ORVs can also allow access for illegal harvest of wildlife in areas that are difficult for game wardens to patrol.  Weaver (1993) reported that increased ORV access increases the trapping vulnerability of American marten, fisher, and wolverine.  For wolves, one study found that 21 of 25 human caused mortalities in the U.S. northern Rockies occurred within 650 ft. of a motorized route (Boyd and Pletscher 1999).  Wolves often travel on roads and off-road vehicle routes where they risk increased poaching pressure.  Several studies have found that wolf persistence is reduced when road density exceeds approximately 1 mi./mi.2 (Table 1). Lynx are also thought to be sensitive to road density, but to a lesser extent than wolves (Singleton et al. 2001, 2002).  Grizzly bears are at risk from poaching and have been found to be negatively affected by roads and to avoid open roads (Elgmork 1978, Zager et al. 1983, Archibald et al. 1987, Mattson et al. 1987, McLellan and Shackleton 1988, Kasworm and Manley 1990, Mace et al. 1996).  


Probably the most widespread impact of ORVs is disturbance to wildlife.  Within individual species, a number of factors can influence the degree of ORV impact, including the animal’s breeding status, its size, and the size of the group it is with (Burger et al. 1995).  Studies have shown a variety of disturbance is possible from ORVs.  While these impacts are difficult to measure, repeated harassment of wildlife can result in increased energy expenditure and reduced reproduction.  Noise and disturbance from ORVs can result in a range of impacts including increased stress (Nash et al. 1970, Millspaugh et al. 2001), loss of hearing (Brattstrom and Bondello 1979), altered movement patterns (e.g., Wisdom et al. 2004, Preisler et al. 2006), avoidance of high-use areas or routes (Janis and Clark 2002, Wisdom 2007), and disrupted nesting activities (e.g., Strauss 1990).

Again, elk are one of the most studied species in regards to disturbance by mechanized use.  Vieira (2000) found that elk moved twice as far from ORV disturbance than they did from pedestrian disturbance, and Wisdom et al. (2004) found that elk moved when ORVs passed within 2,000 yards but tolerated hikers within 500 ft.  Recently, Wisdom (2007) reported preliminary results suggesting that ORVs are causing a shift in the spatial distribution of elk that could increase energy expenditures and decrease foraging opportunities for the herd.  Elk have been found to readily avoid and be displaced from roaded areas (Irwin and Peek 1979, Hershey and Leege 1982, Millspaugh 1995, Weber 1996).  Additional concomitant effects can thus occur, such as major declines in survival of elk calves due to repeated displacement of elk during the calving season (Phillips 1998).  Alternatively, closing or decommissioning roads has been found to decrease elk disturbance (Cole et al. 1997, Millspaugh et al. 2000, Rowland et al. 2005).  

Disruption of breeding and nesting birds is a particularly well documented problem.  Several species are sensitive to human disturbance with the potential disruption of courtship activities, over-exposure of eggs or young birds to weather, and premature fledging of juveniles (Hamann et al. 1999).  Repeated disturbance can eventually lead to nest abandonment.  These short-term disturbances can lead to long-term bird community changes (Anderson et al. 1990).  Several authors have recommended spatial nest buffer zones from motorized recreation for raptors (Table 2).   On the Loa Ranger District of the Fishlake National Forest in southern Utah, successful goshawk nests occur in areas where the localized road density is at or below 2-3 mi./mi.2 (USDA 2005).

Loss of Habitat

The cumulative effect of loss of habitat security, soil erosion, vegetation loss, introduction of non-native invasive species, and forest fragmentation results in the loss of functional wildlife habitat that supports healthy individuals and populations of wildlife.  Animals may be impacted directly and/or indirectly.  A direct impact may be an ORV that collapses a small mammal burrow or runs an animal over.  An indirect impact would be reduced habitat for cavity-nesting species caused by increased access for firewood collection (Bury 1980).  Any additional habitat loss for sensitive, threatened, and endangered species is also of concern. Wilcove et al. (1998) reported that as many as 13 percent of endangered species are impacted by ORVs.

The indirect impacts of ORVs can have cascading effects throughout the ecosystem.  For example, on an intensively used ORV route in Idaho, native shrubs, bunch grasses, and microbiotic crust were greatly reduced close to the route and replaced with non-native cheat grass (Bromus tectorum) and the native shrub, rabbitbrush (Chrysothamnus sp.; Munger et al. 2003). Because of these habitat changes, fewer reptiles were found alongside the route than were found 325 ft. away.  

— Adam is Science Coordinator for Wildlands CPR and Allison is Conservation Biologist for the Wild Utah Project.


Archibald, N.J., R. Ellis, and A.N. Hamilton.  1987.  Responses of grizzly bears to logging truck traffic in the Kimsquit River Valley, British Columbia. International Conference on Bear Research and Management  7: 251-257.
Ashley, P.E., and J.T. Robinson. 1996. Road mortality of amphibians, reptiles and other wildlife on Long Point Causeway, Lake Erie, Ontario. Canadian Field-Naturalist. 110(3): 403-412.
Boyd, D.K., and D.H. Pletscher.  1999.  Characteristics of dispersal in a colonizing wolf population in the central Rocky Mountains. Journal of Wildlife Management 63: 1094-1108.
Brattstrom, B.H., and M.C. Bondello.  1979.  The effects of dune buggy sounds on the telencephalic auditory evoke response in the Mojave fringe-toed lizard, Uma scoparia.  Unpublished report to the U.S. Bureau of Land Management, California Desert Program, Riverside, CA. 31p.
Burcham, M.G., W.D. Edge, L.J. Lyon, C.L. Marcum, and K.T. Weber.  1998.  Final report of the Chamberlain Creek elk studies, 1977-1983 and 1993-1996.  Missoula, MT: School of Forestry, University of Montana. 260p.
Burger, J., M. Gochfeld, and L.J. Niles.  1995.  Ecotourism and birds in coastal New Jersey: contrasting responses of birds, tourists and managers.  Environmental Conservation 22: 56-65.
Bury, R.B.  1980.  What we know and do not know about off-road vehicle impacts on wildlife. in Richard N.L. Andrews and Paul Nowak, editors.  Off-Road Vehicle Use: a Management Challenge. (University of Michigan Extension Service) Michigan League. The University of Michigan, School of Natural Resources. USDA, Office of Environmental Quality.
Call, M.  1979.  Habitat management guides for birds of prey. Bureau of Land Management, Technical Note 338, Denver.  70p.
Cole, E.K., M.D. Pope and R.G. Anthony.  1997.  Effects of road management on movement and survival of Roosevelt elk.  Journal of Wildlife Management 61: 1115-1126.
DeMaynadier, P.G., and M.L. Hunter.  2000.  Road effects on amphibian movements in a forested landscape. Natural Areas Journal 20: 56-65.
Elgmork, K.  1978.  Human impact on a brown bear population (Ursus arctos L.).  Biological Conservation 13(2): 81-103.
Fahrig, L., J.H. Pedlar, S.E. Pope, P.D. Taylor, and J.F. Wegner.  1995.  Effect of road traffic on amphibian density. Biological Conservation 73: 177-182.
Gibbs, J.P. 1998. Amphibian movements in response to forest edges, roads, and stream beds in southern New England. Journal of Wildlife Management 62(2): 584-589.
Gratson, M.W., and C.L. Whitman.  2000.  Characteristics of Idaho elk hunters relative to road access on public lands. Wildlife Society Bulletin 28(4): 1016-1022.
Grigg, J.L.  2007.  Gradients of predation risk affect distribution and migration of a large herbivore.  M.S. Thesis.  Bozeman, MT: Montana State University.
Hershey, T.J., and T.A. Leege.  1982.  Elk movements and habitat use on a managed forest in north-central Idaho.  Idaho Department of Fish and Game. 32p.
Hurley, M.A.  1994.  Summer-fall ecology of the Blackfoot-Clearwater elk herd of western Montana. M.S. Thesis. Moscow, ID: University of Idaho.
Irwin, L.L., and J.M. Peek.  1979.  Relationship between road closure and elk behavior in northern Idaho.  Pages 199-205 in Boyce, M.S. and L.D. Hayden-Wing, editors, North American Elk: Ecology, Behavior, and Management.  Laramie, WY: University of Wyoming.  
Janis, M.W., and J.D. Clark.  2002.  Responses of Florida panthers to recreational deer and hog hunting.  Journal of Wildlife Management 66(3): 839-848.
Jensen W.F., T.K. Fuller, and W.L. Robinson.  1986.  Wolf (Canis lupus) distribution on the Ontario-Michigan border near Sault Ste. Marie.  Canadian Field-Naturalist 100: 363-366.
Jones, S.  1979.  Habitat management series for unique or endangered species. Report No. 17. The accipiters: goshawk, Cooper’s hawk, sharp-shinned hawk. Bureau of Land Management, Technical Note 335.  55p.
Kasworm, W.F., and T.L. Manley.  1990.  Road and trail influences on grizzly bears and black bears in northwest Montana.  Pages 79-84 in Darling, L.M., and W.R. Archibald, editors, Bears – their Biology and Management: Proceedings of the 8th International Conference on Bear Research and Management, February 1989, Victoria, B.C. Bear Biology Association, University of Tennessee, Knoxville.  Pp. 79-84.
Leptich, D.J., and P. Zager.  1991.  Road access management effects on elk mortality and population dynamics.  Pages 126-131 in Proceedings of the elk vulnerability symposium, compilers A.G. Christensen, L.J. Lyon, and T.N.  Bozeman, Montana: Montana State University.
Lyon, L.J.  1983.  Road density models describing habitat effectiveness for elk.  Journal of Forestry 81: 592-595.
Mace, R.D., J.S. Waller, T.L. Manley, L.J. Lyon, and H. Zuuring.  1996.  Relationships among grizzly bears, roads and habitat in the Swan Mountains, Montana. Journal of Applied Ecology 33: 1395-1404.
Mattson, D. J., R. R. Knight, and B. M. Blanchard. 1987. The effects of developments and primary roads on grizzly bear habitat use in Yellowstone National Park, Wyoming. International Conference on Bear Resources and Management 7: 259-273.
McCorquodale, S.M., R. Wiseman, and C.L. Marcum.  2003.  Survival and harvest vulnerability of elk in the Cascade Range of Washington. The Journal of Wildlife Management 67(2): 248-257.
McLellan, B.N., and D.M. Shackleton.  1988.  Grizzly bears and resource-extraction industries: effects of roads on behavior, habitat use, and demography.  Journal of Applied Ecology 25: 451-460.
Mech, L.D., S.H. Fritts, G.L. Radde, and W.J. Paul.  1988.  Wolf distribution and road density in Minnesota. Wildlife Society Bulletin 16: 85-87.
Mech, L.D.  1989.  Wolf population survival in an area of high road density. American Midland Naturalist 121: 387-389.
Millspaugh, J.J.  1995.  Seasonal movements, habitat use patterns and the effects of human disturbances on elk in Custer State Park, South Dakota.  M.S. Thesis. Brookings, SD: South Dakota State University.
Millspaugh, J.J., G.C. Brundige, R.A. Gitzen, and K.J. Raedeke.  2000.  Elk and hunter space-use sharing in South Dakota.  Journal of Wildlife Management 64(4): 994-1003.
Millspaugh, J.J., Woods, R.J. and K.E. Hunt.  2001.  Fecal glucocorticoid assays and the physiological stress response in elk.  Wildlife Society Bulletin 29: 899-907.
Munger, J.C., B.R. Barnett, S.J. Novak, and A.A. Ames.  2003.  Impacts of off-highway motorized vehicle trails on the reptiles and vegetation of the Owyhee Front. Idaho Bureau of Land Management Technical Bulletin 03-3: 1-23.
Nash, R.F., G.G. Gallup, jr., and M.K. McClure.  1970.  The immobility reaction in leopard frogs (Rana pipiens) as a function of noise induced fear.  Psychonometric Science 21(3): 155-156.
Phillips, G.E.  1998.  Effects of human-induced disturbance during calving season on reproductive success of elk in the upper Eagle River Valley.  Dissertation.  Fort Collins, CO: Colorado State University.
Preisler, H.K., A.A. Ager, and M.J. Wisdom.  2006.  Statistical methods for analyzing responses of wildlife to human disturbance.  Journal of Applied Ecology 43: 164-172.
Rei, W., and A. Seitz. 1990. The influence of land use on the genetic structure of populations of the common frog, Rana temporaria. Biological Conservation 54: 239-249.    
Richardson, C.T., and C.K. Miller.  1997.  Recommendations for protecting raptors from human disturbance: a review.  Wildlife Society Bulletin 25: 634-638.
Rowland, M.M., M.J. Wisdom, B.K. Johnson, and M.A. Penninger.  2005.  Effects of roads on elk: implications for management in forested ecosystems.  Pages 42-52 in Wisdom, M.J., technical editor, The Starkey Project: a synthesis of long-term studies of elk and mule deer.  Reprinted from the 2004 Transactions of the North American Wildlife and Natural Resources Conference, Alliance Communications Group, Lawrence, KS.
Singleton, P.H., Gaines, W., and J.F. Lehmkuhl.  2001.  Using weighted distance and least-cost corridor analysis to evaluate regional-scale large carnivore habitat connectivity in Washington.  The Proceedings of the International Conference on Ecology and Transportation, Keystone CO.  September 24-27.
Singleton, P.H., Gaines, W., and J.F. Lehmkuhl.  2002.  Landscape permeability for large carnivores in Washington: A Geographic Information System weighted-distance and least-cost corridor assessment. USDA Forest Service Research Paper.  PNW-RP 549.  Pacific Northwest Field Station, OR.
Strauss, E.G.  1990.  Reproductive success, life history patterns, and behavioral variation in a population of piping plovers subjected to human disturbance.  Dissertation. Medford, MA: Tufts University.
Thiel, R.P. 1985. The relationships between road densities and wolf habitat in Wisconsin. American Midland Naturalist 113: 404-407.
USDA (U.S. Department of Agriculture, Forest Service).  2005.  Fishlake OHV Route Designation Project Draft Environmental Impact Statement (DEIS), Loa, UT.
USFWS (U.S. Fish and Wildlife Service).  1995.  Recovery Plan for the Mexican Spotted Owl (Strix occidentalis lucida).
USDI (U.S. Department of the Interior, Bureau of Land Management).  1987.  Interagency Rocky Mountain Front Wildlife Monitoring / Evaluation Program: management guidelines for selected species, Rocky Mountain Front Studies.  Billings, MT. 71p.
Weaver, J.  1993.  Lynx, wolverine, and fisher in the western United States: research assessment and agenda.  USDA Forest Service Intermountain Research Station Contract Number 43-0353-2-0598. Missoula, MT.
Wilkins, K.T.  1982.  Highways as barriers to rodent dispersal.  Southwest Naturalist 27(4):459-460.
Wilcove, D.S., D. Rothstein, J. Dubow, A. Phillips, and E. Losos.  1998.  Quantifying threats to imperiled species in the United States.  BioScience 48(8): 607-615.
Wisdom, M.J.  2007.  Shift in Spatial Distribution of Elk Away from Trails Used by All-Terrain Vehicles.  Report 1, May 2007, USDA Forest Service, Pacific Northwest Research Station, La Grande, OR.
Wisdom, M.J., H.K. Preisler, N.J. Cimon, and B.K. Johnson.  2004.  Effects of off-road recreation on mule deer and elk. Transactions of the North American Wildlife and Natural Resource Conference 69.
Wydeven, A.P, D.J. Mladenoff, T.A. Sickley, B.E. Kohn, R.P. Thiel, and J.L. Hansen.  2001.  Road density as a factor in habitat selection by wolves and other carnivores in the Great Lakes Region.  Endangered Species Update 18(4): 110-114.
Zager, P.E., C.J. Jonkel, and J. Habeck.  1983.  Logging and wildfire influence on grizzly bear habitat in Northwestern Montana. International Conference on Bear Resources and Management 5: 124-132.