Tooth and Claw: Ecological Effects of Roads on Predators
Predators stand out among terrestrial fauna as the group most susceptible to the adverse impacts of roads. Positioned high in the food chain, predators have evolved to live long natural lives, rear their young over a protracted period, and generally have low reproductive rates. All of these factors combine to create an extremely low tolerance to increased mortality.
Because of their extensive home ranges, many predatory species also stand out as umbrella species for managementthat is, if we protect predators and their habitats, then this protective "umbrella" will be large enough to include the habitat needs for other species that coexist with predators (Noss et al. 1996). Unfortunately, predators' unique combination of sensitivity to mortality and broad habitat needs has led increasingly to their imperilment. Road and access management is crucial to the long-term survival of predators (see RIPorters V3#3 and V2#6 for Bibliography Notes on grizzly bear and wild cats).
Fender Fodder
Direct mortality from roadsin the form of vehicle-predator collisionscan devastate predator populations, especially when they are isolated geographically or rare in number (Forman et al. 1996). In some cases, such as that of the Florida panther, death by auto has been cited as one of the primary causes of a species' imperilment. Before 1991, 47% of known Florida panther deaths were from road kill, though highway underpasses installed since that time appear to be reducing direct mortality substantially (Foster and Humphrey 1995; Smith et al. 1996). In Denmark, roadkill accounted for 3600 badger deathsor 10-15% of the species' total population in that nationin a single year (Aaris-Sorensen 1995). Roadkills represent 46% of all human-related mortality for the endangered American crocodile (Smith et al. 1996), and are considered the major cause of mortality for the ocelot, an endangered North American cat (Jenkins 1996).
Beyond Bumpers
Indirect impacts from roadssuch as habitat fragmentation, direct habitat loss, increased human development, increased motorized access, and habitat displacementalso account for substantial human-caused mortality of predators (Ruediger 1996). Additionally, prey species such as elk (Lyon 1983), moose (Crete et al. 1981; Timmerman and Gallath 1982), and deer (Sage et al. 1983) are sensitive to road densities and as their populations decline their predators drop in number accordingly.
When roads slice through formerly-unbroken habitat areas, the resultant openings affect species' abilities to hunt, find cover, or den. This fragmentation also facilitates the spread of noxious weeds and affects the native plant populations upon which herbivores and subsequently predators depend. The degree of habitat fragmentation generally correlates with road density, which is determined by calculating the miles of road per square mile of land.
Road densities greater than 1 mile/square mile have been shown to reduce habitat security and increase mortality for a range of predators, including grizzly and black bears, and lynx (Britell et al. 1989; Naney 1991; Noss 1996 citing Brody and Pelton 1989). A 1996 study of Montana grizzly bears found that animals avoided areas of high road density even though roads were closed to public use (Mace et al. 1996). Studies in southern Utah and the northern Great Lakes have shown that mountain lions and wolves, respectively, fail to survive when road density exceeds 0.9 miles/square mile (Thiel 1985; Van Dyke et al. 1986; Jensen et al. 1986; Mech et al. 1988). Mech (1989) later determined that wolves could survive in areas with higher road density only if they existed adjacent to roadless lands populated by wolves.
Swift fox present one of the few exceptions to the array of predators that are known to avoid roads. Whether due to easier hunting in the short grasses near roadsides, trying to avoid their own most common predator (coyotes), or for some other yet-unknown reason (like becoming more visible to researchers), swift fox show a strong preference for roads and typically den within 230 meters of them (Hines and Case 1991). Whatever the motive, swift foxes' affinity for roadsides exacts a toll as they suffer high levels of juvenile mortality to roadkill (Sovada et al. 1998).
Roads create an obvious source of mortality from trapping, hunting, or poaching due to easy motorized access. A Minnesota study, for instance, found that 91% of all black bear deaths were caused by legal and illegal hunting (Rogers 1987), and in roaded areas of Maine trapping accounted for 90% of all pine marten deaths (Hodgman et al. 1994). Not surprisingly, the danger and noise associated with roads typically create an avoidance response by predators. An ongoing study in British Columbia has found wolverine den sites exclusively in roadless drainages (Krebs 1998). Lynx generally will not cross openings greater than 100 feet (Naney 1991), bobcats avoid roads and habitat within 100 meters of roadsides (Lovello and Anderson 1996), grizzly bears are disrupted up to a distance of 4 kilometers by roads (Mattson et al. 1987), and in Africa black-backed jackals avoid areas within 600 meters of a roadway (Newmark et al. 1996). Spanish predators, including the Iberian lynx, red fox, wild cat, and common genet avoid road crossings by using culvert tunnels beneath roadways (Rodriguez et al. 1996).
Conclusion
While highway underpasses, wildlife culverts, and other measures can sometimes mitigate the direct impacts of roadkill, predators will continue to suffer world-wide declines if present road-building trends continue. With an estimated 10% of the contiguous United States already directly impacted by roads (Forman et al. 1996), there are simply too many roads exerting too much damage in too many places for predators to rebound on their own. It remains critically important to predators' survival in North America and elsewhere that activists and land managers work to remove the most ecologically destructive roads and prevent new roads from being built into existing habitat.
David Havlick has an MS from the University of Montana and coordinates the Roads Scholar Project for Predator Project.
Bibliography
Aaris-Sorensen, J. 1995. Road-kills of badgers (Meles meles) in Denmark. Annales Zoologici Fennici 32(1): 31-36.
Britell, J.D., R.J. Toelker, S.J. Sweeney, and G.M. Koehler. 1989. Native Cats of Washington. Washington Department of Wildlife. Olympia, WA.
Brody, A.J. and M.R. Pelton. 1989. Effects of roads on black bear movements in North Carolina. Wildlife Society Bulletin 17: 5-10.
Crete, M., R.J. Taylor, and P.A. Jordan. 1981. Optimization of moose harvest in southwestern Quebec. Journal of Wildlife Management 45: 598-611.
Forman, R.T.T., D.S. Friedman, D. Fitzhenry, J.D. Martin, A.S. Chen and L.E. Alexander. 1996. Ecological effects of roads: Toward three summary indices and an overview for North America. In press: Habitat Fragmentation and Infrastructure. Canters, K., ed. Ministry of Transport, Public Works and Water Management, Delft, Netherlands.
Foster, M.L. and S.R. Humphrey. 1995. Use of highway underpasses by Florida panthers and other wildlife. Wildlife Society Bulletin 23: 95-100.
Hines, T.D., and R.M. Case. 1991. Diet, home range, movements and activity periods of swift fox in Nebraska. Prairie Naturalist 23: 131-138.
Hodgman, T.P., Harrison, D.J., Katnik, D.D. and K.D. Elowe. 1994. Survival in an intensively trapped marten population in Maine. Journal of Wildlife Management 58 (4): 593-599.
Jenkins, K. 1996. Texas Department of Transportation wildlife activities. Florida DOT Report, FL-ER-58-96, Tallahassee, FL. Pp. 199-231.
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.
Krebs, J. 1998. Senior Wildlife Biologist. Personal communication with David Gaillard, Predator Project staff June 16, 1998. British Columbia, Canada, Ministry of Environment Study, in progress.
Lovello, M.J. and E.M. Anderson. 1996. Bobcat movement and home ranges relative to roads in Wisconsin. Wildlife Society Bulletin 24(1): 71-76.
Lyon, L.J. 1983. Road density models describing habitat effectiveness for elk. Journal of Forestry 81: 592-595, 613.
Mace, R.D., J. Waller, T. 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. Knight and B. Blanchard. 1987. The effects of developments and primary road systems on grizzly bear habitat use in Yellowstone National Park, Wyoming. In: International Conference on Bear Research and Management. 7: 259-273.
Mech, L.D. 1989. Wolf population survival in an area of high road density. American Midland Naturalist 121: 387-389.
Mech, L.D., S.H. Fritts, G.L. Radde and W.J. Paule. 1988. Wolf distribution and road density in Minnesota. Wildlife Society Bulletin 16: 85-87.
Naney, R. 1991. USDA Forest Service Region One. Lynx, Fisher, and Wolverine Coordination Meeting.
Newmark, W.D., J.I. Boshe, H.I. Sariko, and G.K. Makumbule. 1996. Effects of a highway on large mammals in Mikumi National Park, Tanzania. African Journal of Ecology, 34(1): 15-31.
Noss, R. August 1996. "The Ecological Effects of Roads," Road-Ripper's Handbook, ROAD-RIP, Missoula, MT.
Noss, R.F., Quigley, H.B. Hornocker, M.G., Merrill, T. and P.C. Paquet. 1996. Conservation biology and carnivore conservation in the Rocky Mountains. Conservation Biology 10(4): 949-963.
Rodriguez, A., G. Crema and M. Delibes. 1996. Use of non-wildlife passages across a high speed railway by terrestrial vertebrates. Journal of Applied Ecology 33: 1527-1540.
Rogers, L.L. 1987. Effects of food supply and kinship of social behavior, movements and population growth of black bears in northwestern Minnesota. Wildlife Monographs 97. 73 pp.
Ruediger, Bill. 1996. The relationship between rare carnivores and highways. In: Trends in Addressing Transportation Related Wildlife Mortality, proceedings from the Transportation Related Wildlife Mortality Seminar, edited by G. Evink, D. Ziegler, P. Garrett and J. Berry. Florida DOT, Tallahassee, FL. Pp. 24-38.
Sage, R.W., W.C. Tierson, G.F. Mattfield, and D.F. Behrend. 1983. White-tailed deer visibility and behavior along forest roads. Journal of Wildlife Management 47: 940-962.
Smith, D.J., L.D. Harris and F.J. Mazzotti. 1996. A landscape approach to examining the impacts of roads on the ecological function associated with wildlife movement and movement corridors: problems and solutions. Florida DOT Report FL-ER-58-96, Tallahassee, Florida. Pp. 301-315.
Sovada, M.A., C.C. Roy and R.O. Woodward. 1998. Swift fox mortality in grassland and cropland landscapes of western Kansas. Unpublished report presented at Swift Fox Symposium, Saskatoon, Saskatchewan, Canada.
Thiel, R.P. 1985. Relationship between road densities and wolf habitat suitability in Wisconsin. American Midland Naturalist 113: 404-407.
Timmerman, H.R. and R. Gollath. 1982. Age and sex structure of harvested moose related to season manipulation and access. Alces 18: 301-328.
Van Dyke, F.B., R.H. Brocke. H.G. Shaw., B.B. Ackerman., T.P. Hemker and F.G. Lindzey. 1986. Reactions of mountain lions to logging and human activity. Journal of Wildlife Managment 50: 95-102.
Because of their extensive home ranges, many predatory species also stand out as umbrella species for managementthat is, if we protect predators and their habitats, then this protective "umbrella" will be large enough to include the habitat needs for other species that coexist with predators (Noss et al. 1996). Unfortunately, predators' unique combination of sensitivity to mortality and broad habitat needs has led increasingly to their imperilment. Road and access management is crucial to the long-term survival of predators (see RIPorters V3#3 and V2#6 for Bibliography Notes on grizzly bear and wild cats).
Fender Fodder
Direct mortality from roadsin the form of vehicle-predator collisionscan devastate predator populations, especially when they are isolated geographically or rare in number (Forman et al. 1996). In some cases, such as that of the Florida panther, death by auto has been cited as one of the primary causes of a species' imperilment. Before 1991, 47% of known Florida panther deaths were from road kill, though highway underpasses installed since that time appear to be reducing direct mortality substantially (Foster and Humphrey 1995; Smith et al. 1996). In Denmark, roadkill accounted for 3600 badger deathsor 10-15% of the species' total population in that nationin a single year (Aaris-Sorensen 1995). Roadkills represent 46% of all human-related mortality for the endangered American crocodile (Smith et al. 1996), and are considered the major cause of mortality for the ocelot, an endangered North American cat (Jenkins 1996).
Beyond Bumpers
Indirect impacts from roadssuch as habitat fragmentation, direct habitat loss, increased human development, increased motorized access, and habitat displacementalso account for substantial human-caused mortality of predators (Ruediger 1996). Additionally, prey species such as elk (Lyon 1983), moose (Crete et al. 1981; Timmerman and Gallath 1982), and deer (Sage et al. 1983) are sensitive to road densities and as their populations decline their predators drop in number accordingly.
When roads slice through formerly-unbroken habitat areas, the resultant openings affect species' abilities to hunt, find cover, or den. This fragmentation also facilitates the spread of noxious weeds and affects the native plant populations upon which herbivores and subsequently predators depend. The degree of habitat fragmentation generally correlates with road density, which is determined by calculating the miles of road per square mile of land.
Road densities greater than 1 mile/square mile have been shown to reduce habitat security and increase mortality for a range of predators, including grizzly and black bears, and lynx (Britell et al. 1989; Naney 1991; Noss 1996 citing Brody and Pelton 1989). A 1996 study of Montana grizzly bears found that animals avoided areas of high road density even though roads were closed to public use (Mace et al. 1996). Studies in southern Utah and the northern Great Lakes have shown that mountain lions and wolves, respectively, fail to survive when road density exceeds 0.9 miles/square mile (Thiel 1985; Van Dyke et al. 1986; Jensen et al. 1986; Mech et al. 1988). Mech (1989) later determined that wolves could survive in areas with higher road density only if they existed adjacent to roadless lands populated by wolves.
Swift fox present one of the few exceptions to the array of predators that are known to avoid roads. Whether due to easier hunting in the short grasses near roadsides, trying to avoid their own most common predator (coyotes), or for some other yet-unknown reason (like becoming more visible to researchers), swift fox show a strong preference for roads and typically den within 230 meters of them (Hines and Case 1991). Whatever the motive, swift foxes' affinity for roadsides exacts a toll as they suffer high levels of juvenile mortality to roadkill (Sovada et al. 1998).
Roads create an obvious source of mortality from trapping, hunting, or poaching due to easy motorized access. A Minnesota study, for instance, found that 91% of all black bear deaths were caused by legal and illegal hunting (Rogers 1987), and in roaded areas of Maine trapping accounted for 90% of all pine marten deaths (Hodgman et al. 1994). Not surprisingly, the danger and noise associated with roads typically create an avoidance response by predators. An ongoing study in British Columbia has found wolverine den sites exclusively in roadless drainages (Krebs 1998). Lynx generally will not cross openings greater than 100 feet (Naney 1991), bobcats avoid roads and habitat within 100 meters of roadsides (Lovello and Anderson 1996), grizzly bears are disrupted up to a distance of 4 kilometers by roads (Mattson et al. 1987), and in Africa black-backed jackals avoid areas within 600 meters of a roadway (Newmark et al. 1996). Spanish predators, including the Iberian lynx, red fox, wild cat, and common genet avoid road crossings by using culvert tunnels beneath roadways (Rodriguez et al. 1996).
Conclusion
While highway underpasses, wildlife culverts, and other measures can sometimes mitigate the direct impacts of roadkill, predators will continue to suffer world-wide declines if present road-building trends continue. With an estimated 10% of the contiguous United States already directly impacted by roads (Forman et al. 1996), there are simply too many roads exerting too much damage in too many places for predators to rebound on their own. It remains critically important to predators' survival in North America and elsewhere that activists and land managers work to remove the most ecologically destructive roads and prevent new roads from being built into existing habitat.
David Havlick has an MS from the University of Montana and coordinates the Roads Scholar Project for Predator Project.
Bibliography
Aaris-Sorensen, J. 1995. Road-kills of badgers (Meles meles) in Denmark. Annales Zoologici Fennici 32(1): 31-36.
Britell, J.D., R.J. Toelker, S.J. Sweeney, and G.M. Koehler. 1989. Native Cats of Washington. Washington Department of Wildlife. Olympia, WA.
Brody, A.J. and M.R. Pelton. 1989. Effects of roads on black bear movements in North Carolina. Wildlife Society Bulletin 17: 5-10.
Crete, M., R.J. Taylor, and P.A. Jordan. 1981. Optimization of moose harvest in southwestern Quebec. Journal of Wildlife Management 45: 598-611.
Forman, R.T.T., D.S. Friedman, D. Fitzhenry, J.D. Martin, A.S. Chen and L.E. Alexander. 1996. Ecological effects of roads: Toward three summary indices and an overview for North America. In press: Habitat Fragmentation and Infrastructure. Canters, K., ed. Ministry of Transport, Public Works and Water Management, Delft, Netherlands.
Foster, M.L. and S.R. Humphrey. 1995. Use of highway underpasses by Florida panthers and other wildlife. Wildlife Society Bulletin 23: 95-100.
Hines, T.D., and R.M. Case. 1991. Diet, home range, movements and activity periods of swift fox in Nebraska. Prairie Naturalist 23: 131-138.
Hodgman, T.P., Harrison, D.J., Katnik, D.D. and K.D. Elowe. 1994. Survival in an intensively trapped marten population in Maine. Journal of Wildlife Management 58 (4): 593-599.
Jenkins, K. 1996. Texas Department of Transportation wildlife activities. Florida DOT Report, FL-ER-58-96, Tallahassee, FL. Pp. 199-231.
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.
Krebs, J. 1998. Senior Wildlife Biologist. Personal communication with David Gaillard, Predator Project staff June 16, 1998. British Columbia, Canada, Ministry of Environment Study, in progress.
Lovello, M.J. and E.M. Anderson. 1996. Bobcat movement and home ranges relative to roads in Wisconsin. Wildlife Society Bulletin 24(1): 71-76.
Lyon, L.J. 1983. Road density models describing habitat effectiveness for elk. Journal of Forestry 81: 592-595, 613.
Mace, R.D., J. Waller, T. 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. Knight and B. Blanchard. 1987. The effects of developments and primary road systems on grizzly bear habitat use in Yellowstone National Park, Wyoming. In: International Conference on Bear Research and Management. 7: 259-273.
Mech, L.D. 1989. Wolf population survival in an area of high road density. American Midland Naturalist 121: 387-389.
Mech, L.D., S.H. Fritts, G.L. Radde and W.J. Paule. 1988. Wolf distribution and road density in Minnesota. Wildlife Society Bulletin 16: 85-87.
Naney, R. 1991. USDA Forest Service Region One. Lynx, Fisher, and Wolverine Coordination Meeting.
Newmark, W.D., J.I. Boshe, H.I. Sariko, and G.K. Makumbule. 1996. Effects of a highway on large mammals in Mikumi National Park, Tanzania. African Journal of Ecology, 34(1): 15-31.
Noss, R. August 1996. "The Ecological Effects of Roads," Road-Ripper's Handbook, ROAD-RIP, Missoula, MT.
Noss, R.F., Quigley, H.B. Hornocker, M.G., Merrill, T. and P.C. Paquet. 1996. Conservation biology and carnivore conservation in the Rocky Mountains. Conservation Biology 10(4): 949-963.
Rodriguez, A., G. Crema and M. Delibes. 1996. Use of non-wildlife passages across a high speed railway by terrestrial vertebrates. Journal of Applied Ecology 33: 1527-1540.
Rogers, L.L. 1987. Effects of food supply and kinship of social behavior, movements and population growth of black bears in northwestern Minnesota. Wildlife Monographs 97. 73 pp.
Ruediger, Bill. 1996. The relationship between rare carnivores and highways. In: Trends in Addressing Transportation Related Wildlife Mortality, proceedings from the Transportation Related Wildlife Mortality Seminar, edited by G. Evink, D. Ziegler, P. Garrett and J. Berry. Florida DOT, Tallahassee, FL. Pp. 24-38.
Sage, R.W., W.C. Tierson, G.F. Mattfield, and D.F. Behrend. 1983. White-tailed deer visibility and behavior along forest roads. Journal of Wildlife Management 47: 940-962.
Smith, D.J., L.D. Harris and F.J. Mazzotti. 1996. A landscape approach to examining the impacts of roads on the ecological function associated with wildlife movement and movement corridors: problems and solutions. Florida DOT Report FL-ER-58-96, Tallahassee, Florida. Pp. 301-315.
Sovada, M.A., C.C. Roy and R.O. Woodward. 1998. Swift fox mortality in grassland and cropland landscapes of western Kansas. Unpublished report presented at Swift Fox Symposium, Saskatoon, Saskatchewan, Canada.
Thiel, R.P. 1985. Relationship between road densities and wolf habitat suitability in Wisconsin. American Midland Naturalist 113: 404-407.
Timmerman, H.R. and R. Gollath. 1982. Age and sex structure of harvested moose related to season manipulation and access. Alces 18: 301-328.
Van Dyke, F.B., R.H. Brocke. H.G. Shaw., B.B. Ackerman., T.P. Hemker and F.G. Lindzey. 1986. Reactions of mountain lions to logging and human activity. Journal of Wildlife Managment 50: 95-102.