An Evaluation Of Wildlife Crossing Structures: Their Use And Effectiveness
The study of road impacts upon wildlife has ignited in the last decade, but only in the past few years have efforts begun to mitigate these impacts. Engineers and biologists are now working jointly to design operative wildlife underpasses and overpasses that will temper the effect roads have upon wildlife. Effective crossing structures will help to reconnect areas of viable habitat that have become isolated due to road construction. This is an arduous task if you consider the wide-ranging species in the world, their diverse biological needs and habitat requirements.
In the last decade, wildlife crossing structures ranging from amphibian tunnels to large carnivore open span bridges have been built to combat roadkill and road avoidance. With the passage of a new federal highway bill in the U.S. Congress, the Transportation Equity Act (TEA-21), federal support is available for wildlife crossing structures on both new and existing roads in the United States. The European Union passed a similar measure, COST-341. Both initiatives have heightened the concern for sustainable transportation systems and incorporation of mitigation structures into road plans (Gloyne and Clevenger, 2001).
Only limited information exists on the efficacy of those structures that are just now gaining nationwide and global support. Biologists and engineers are on a learning curve, and future studies are needed to determine what attributes will make these structures most effective for the greatest number of species. Although the need for more research is apparent, preliminary studies from Europe, Canada, and the United States have provided some insight concerning significant features/issues that should be considered when building wildlife crossing structures.
Wildlife crossing structures come in many sizes and shapes; their features ultimately depending upon the ecological and behavioral needs of the diverse species that inhabit an area. Each species has different needs, therefore, when designing these structures it is virtually impossible to accommodate all species in an area. A more generalized approach should be taken to make highways permeable for as many species as possible. îToday highway planners and land mangers can ill afford the naïve luxury of single-species mitigation structures. Species do not function in isolation but are components of ecological systems that inherently fall into the category of organized complexity. Therefore, any singlespecies mitigation structure is likely to have cascading effects, some positive and some negative, on non-target species also. If a mitigation structure is to succeed, a multi-species approach is needed to evaluate the efficacy of such mitigation on non-target species as well" (Clevenger and Waltho 2000).
Various attributes of crossing structures such as light, noise, substrate, natural cover, dimensions, and placement will determine usage by different species. Most studies indicate that the larger the underpass/overpass, the better suited it will be to accommodate a wide range of species (Reed 1981, De Santo and Smith 1993, and Jackson and Curtice 1998). Natural vegetation near the opening will give both large and small species the security of their preferred environment (Rodriguez et al. 1996, Hunt et al. 1992, Clevenger et al. 2001a). Vegetation can serve as a funneling system, guiding animals to the openings, thus helping to motivate them to use the crossing structure (Yanes et al. 1995).
Proper placement of the crossing structure is likely the most important feature in determining success (Jackson and Curtice 1998, Rodriguez et al. 1996, Land and Lotz 1996, Singer et al. 1985). Most studies indicate that placing the crossing structure near traditional migration routes will increase effectiveness. Methods to determine proper placement are track count surveys, monitoring trails with infrared cameras, GIS modeling to determine likely travel corridors, roadkill data, and radio tracking collared animals (Scheick and Jones). In addition, some biologists recommend that crossing structures be placed away from human disturbance areas; human activity has been negatively correlated with underpass/overpass use.
Underpasses and overpasses will be more effective if they are accompanied by fencing on both sides of a road. Fences were primarily erected to reduce roadkill, however, without a crossing structure, fencing further reduces a roadøs permeability. Most studies indicate that fencing should be about eight feet tall (Groot Bruinderink and Hazelbrook 1996, Sipes and Neff 2001). Fencing should be built around the crossing structure to guide (funnel) animals to the passageway, thus preventing them from circumventing the system (Jackson and Curtice 1998).
Are These Structures Effective?
Crossing structures are slowly being incorporated into the road plans of transportation agencies around the globe, however, very little research has been done on their true effectiveness. îThis is a field of applied ecology still very much in its infancy," says Parks Canada researcher TonyClevenger (Wilkinson 2000). Clevenger also adds that virtually nothing is known about the relative effectiveness of overpasses and underpasses, or between the different types ofunderpasses being tested (Clevenger 1998). We can infer what features are most important based on the studies that have been conducted so far, but no study has been able to accuratelyestimate how many animal crossings would have occurred if a given structure was not there.
Knowledge of the abundance and distribution of populations is essential in developing criteria to measure crossing effectiveness (Clevenger 1999). To try and obtain expected crossing rates, movement patterns, population densities, and life history requirements, years of study are needed. îAnswering some of the complex ecological questions around roads and long-lived wildlife like bears may require research timeframes of up to 10-15 years" (Whyte Museum 2000). Even then, biologists will need to take into consideration that a low crossing rate may be due to a natural fluctuation/decline in wildlife populations. Low crossing rates may also be attributed to the time it takes certain species to adapt to and use a crossing structure.
Although more studies are needed to determine effectiveness, the crossing structures and fencing erected in areas such as Banff National Park, Glacier National Park, Florida and Europe have dramatically decreased roadkill and have allowed for numerous wildlife passages. In some cases the carnage on roads has decreased as much as 97%, and wildlife ranging from salamanders to large grizzly bears and panthers are passing through the structures to reach vital habitat.
Conclusion
Wildlife crossing structures have had some great successes. They have been useful in decreasing roadkill, and have been successful in enhancing landscape connectivity. The dearth of information on their effectiveness makes further studies essential if biologists and engineers are expected to make the crossings even better for a diverse array of wildlife (Clevenger 1998). Regardless of how much data is collected, there will never be one perfect structure to suit all speciesø needs (Clevenger and Hardy pers. comm.). Therefore, îour first choice would always be to not build a road through wildlife habitat" (Lavendel 2000). For already existing roads, wildlife passages should be added thoughtfully with all species considerations in mind. The following list provides some salient recommendations to consider when developing or monitoring wildlife crossing structures:
* Take a multi-species approach rather than a single-species focus, remembering that species do not function in isolation but are components of ecological systems;
* Know the biology of the species in the area, their distribution, abundance, and ecological and behavioral needs;
* Place the structures at known migration routes, away from human disturbance. This can be determined by roadkill data, infrared cameras, GIS modeling, and track-count surveys;
* Make the passages wide to accommodate a larger number of species;
* Try to build structures to allow for natural lighting and low noise levels;
* Have a clear view to the other side;
* Use fencing designed to reduce wildlife intrusions;
* Conduct intensive monitoring before and after constructing the wildlife passages via track count surveys, radio-collaring, mark-recapture studies, etc., and;
* Share the results!
It is imperative that biologists and engineers share their findings and ideas concerning crossing structure effectiveness. Events such as the International Conference on Wildlife Ecology and Transportation have become integral to this process. Ideally, the knowledge gained from these meetings will lead to the design of improved crossing structures that will more effectively connect the habitats of a diversity of wildlife.
--- Maureen Hartmann is a graduate student in Environmental Studies at the University of Montana.
Literature Cited
Clevenger, A.P. 1998. Permeability of the Trans-Canada Highway to wildlife in Banff National Park: Importance of crossing structures and factors influencing their effectiveness. Pp.109-119. In G.L. Evink, P.A. Garrett, D. Zeigler, and J. Berry, eds. Proceedings of the International Conference on Wildlife Ecology and Transportation. Feb. 10-12, 1998 Fort Myers, FL. FL DOT FL-ER 69-98.
Clevenger, A.P. and Nigel Waltho. 2000. Factors influencing the effectiveness of wildlife underpasses in Banff National Park, Alberta, Canada. Conservation Biology. 14(1): 47-56.
DeSanto, R.S. and D.G. Smith. 1993. Environmental auditing: An introduction to issues of habitat fragmentation relative to transportation corridors with special reference to high-speed rail (HSR). Environmental Management. 17(1): 111-114.
Gloyne, C.C. and A.P. Clevenger. 2001. Cougar (puma concolor) use of wildlife crossing structures on the Trans Canada highway in Banff National Park, Alberta. Wildlife Biology. 7(2): 117-124.
Groot Bruinderink, G.W.T.A. and E. Hazelbrook. 1996. Ungulate traffic collisions in europe. Conservation Biology. 10(4):1059-1067.
Hunt, A., H.J. Dickens, and R.J. Whelan. 1987. Movement of mammals through tunnels under railway lines. Australian Zoologist. 24(2) 89-93.
Jackson, S.D. and G.R. Curtice. 1998. Toward a practical strategy for mitigating highway impacts on wildlife. Pp. 17-22 in G.L. Evink, P.A. Garrett, D. Zeigler, and J. Berry, eds. Proceedings of the International Conference on Wildlife Ecology and Transportation. Feb. 10-12, 1998 Fort Myers, FL. FL DOT FL-ER 69-98.
Land, D. and M. Lotz. 1996. Wildlife crossing designs and use by florida panthers and other wildlife in southwest Florida. In G.L. Evink, P.A. Garrett, D. Zeigler, and J. Berry, eds. Proceedings of the International Conf. on Wildlife Ecology and Transportation. June, 1996. Tallahassee, FL. FL DOT FL-ER 58-96.
Lavendel, Brian. 2000. Putting the breaks on roadkill. Animals. 133(6):20-23.
Mansergh, I.M., and Scotts, D.J. 1989. Habitat continuity and social organization of the mountain pygmy-possum restored by tunnel. Journal of Wildlife Management. 53(3):701-707.
Rodriguez, A., G. Crema, and M. Delibes. 1996. Use of nonwildlife passages across a high speed railway by terrestrial vertebrates. Journal of Applied Ecology. 33:1527-1540.
Reed, Dale. 1981. Mule deer behavior at a highway underpass exit. Journal of Wildlife Management. 45(2):542-543.
Savage, Candace. 2000. A highway runs through it. Canadian Geographic. 120(5): 35-42.
Scheick, B.K. and M.D. Jones. Locating wildlife underpasses prior to expansion of highway 64 in North Carolina. North Carolina Wildlife Resources Commission, Plymouth and Bridgeton, North Carolina. www.myflorida.com/emo/sched/locate.pdf.
Servheen, C. 2001. U.S. Fish and Wildlife Service Grizzly Bear Recovery Coordinator. Personal Communication Nov, 2001.
Singer, F.J., W.L. Langlitz, and E.C. Samuelson. 1985. Design and construction of highway underpasses used by mountain goats. Transportation Research Record. 1016:6-10.
Sipes, J.L. and J. Neff. 2001. Fencing, wildlife crossings, and roads: separating animals and vehicles. Landscape Architecture. 91(6):24-27.
Whyte Museum. 2000. Mitigation: Reducing the Impacts of Roads and Railways on Bears. http://www.whyte.org/bears/ mitigate.html.
Wilkinson, Todd. Making the road safe ¤ for elk, bears, and wolves. The Christian Science Monitor. 12/09/00. http://www.csmonitor.com/durable/2000/12/19/text/p3sl.html.
Yanes, M., J.M. Velasco, and F. Suarez. 1995. Permeability of roads and railways to vertebrates: The importance of culverts. Biological Conservation. 71:217-222.
In the last decade, wildlife crossing structures ranging from amphibian tunnels to large carnivore open span bridges have been built to combat roadkill and road avoidance. With the passage of a new federal highway bill in the U.S. Congress, the Transportation Equity Act (TEA-21), federal support is available for wildlife crossing structures on both new and existing roads in the United States. The European Union passed a similar measure, COST-341. Both initiatives have heightened the concern for sustainable transportation systems and incorporation of mitigation structures into road plans (Gloyne and Clevenger, 2001).
Only limited information exists on the efficacy of those structures that are just now gaining nationwide and global support. Biologists and engineers are on a learning curve, and future studies are needed to determine what attributes will make these structures most effective for the greatest number of species. Although the need for more research is apparent, preliminary studies from Europe, Canada, and the United States have provided some insight concerning significant features/issues that should be considered when building wildlife crossing structures.
Wildlife crossing structures come in many sizes and shapes; their features ultimately depending upon the ecological and behavioral needs of the diverse species that inhabit an area. Each species has different needs, therefore, when designing these structures it is virtually impossible to accommodate all species in an area. A more generalized approach should be taken to make highways permeable for as many species as possible. îToday highway planners and land mangers can ill afford the naïve luxury of single-species mitigation structures. Species do not function in isolation but are components of ecological systems that inherently fall into the category of organized complexity. Therefore, any singlespecies mitigation structure is likely to have cascading effects, some positive and some negative, on non-target species also. If a mitigation structure is to succeed, a multi-species approach is needed to evaluate the efficacy of such mitigation on non-target species as well" (Clevenger and Waltho 2000).
Various attributes of crossing structures such as light, noise, substrate, natural cover, dimensions, and placement will determine usage by different species. Most studies indicate that the larger the underpass/overpass, the better suited it will be to accommodate a wide range of species (Reed 1981, De Santo and Smith 1993, and Jackson and Curtice 1998). Natural vegetation near the opening will give both large and small species the security of their preferred environment (Rodriguez et al. 1996, Hunt et al. 1992, Clevenger et al. 2001a). Vegetation can serve as a funneling system, guiding animals to the openings, thus helping to motivate them to use the crossing structure (Yanes et al. 1995).
Proper placement of the crossing structure is likely the most important feature in determining success (Jackson and Curtice 1998, Rodriguez et al. 1996, Land and Lotz 1996, Singer et al. 1985). Most studies indicate that placing the crossing structure near traditional migration routes will increase effectiveness. Methods to determine proper placement are track count surveys, monitoring trails with infrared cameras, GIS modeling to determine likely travel corridors, roadkill data, and radio tracking collared animals (Scheick and Jones). In addition, some biologists recommend that crossing structures be placed away from human disturbance areas; human activity has been negatively correlated with underpass/overpass use.
Underpasses and overpasses will be more effective if they are accompanied by fencing on both sides of a road. Fences were primarily erected to reduce roadkill, however, without a crossing structure, fencing further reduces a roadøs permeability. Most studies indicate that fencing should be about eight feet tall (Groot Bruinderink and Hazelbrook 1996, Sipes and Neff 2001). Fencing should be built around the crossing structure to guide (funnel) animals to the passageway, thus preventing them from circumventing the system (Jackson and Curtice 1998).
Are These Structures Effective?
Crossing structures are slowly being incorporated into the road plans of transportation agencies around the globe, however, very little research has been done on their true effectiveness. îThis is a field of applied ecology still very much in its infancy," says Parks Canada researcher TonyClevenger (Wilkinson 2000). Clevenger also adds that virtually nothing is known about the relative effectiveness of overpasses and underpasses, or between the different types ofunderpasses being tested (Clevenger 1998). We can infer what features are most important based on the studies that have been conducted so far, but no study has been able to accuratelyestimate how many animal crossings would have occurred if a given structure was not there.
Knowledge of the abundance and distribution of populations is essential in developing criteria to measure crossing effectiveness (Clevenger 1999). To try and obtain expected crossing rates, movement patterns, population densities, and life history requirements, years of study are needed. îAnswering some of the complex ecological questions around roads and long-lived wildlife like bears may require research timeframes of up to 10-15 years" (Whyte Museum 2000). Even then, biologists will need to take into consideration that a low crossing rate may be due to a natural fluctuation/decline in wildlife populations. Low crossing rates may also be attributed to the time it takes certain species to adapt to and use a crossing structure.
Although more studies are needed to determine effectiveness, the crossing structures and fencing erected in areas such as Banff National Park, Glacier National Park, Florida and Europe have dramatically decreased roadkill and have allowed for numerous wildlife passages. In some cases the carnage on roads has decreased as much as 97%, and wildlife ranging from salamanders to large grizzly bears and panthers are passing through the structures to reach vital habitat.
Conclusion
Wildlife crossing structures have had some great successes. They have been useful in decreasing roadkill, and have been successful in enhancing landscape connectivity. The dearth of information on their effectiveness makes further studies essential if biologists and engineers are expected to make the crossings even better for a diverse array of wildlife (Clevenger 1998). Regardless of how much data is collected, there will never be one perfect structure to suit all speciesø needs (Clevenger and Hardy pers. comm.). Therefore, îour first choice would always be to not build a road through wildlife habitat" (Lavendel 2000). For already existing roads, wildlife passages should be added thoughtfully with all species considerations in mind. The following list provides some salient recommendations to consider when developing or monitoring wildlife crossing structures:
* Take a multi-species approach rather than a single-species focus, remembering that species do not function in isolation but are components of ecological systems;
* Know the biology of the species in the area, their distribution, abundance, and ecological and behavioral needs;
* Place the structures at known migration routes, away from human disturbance. This can be determined by roadkill data, infrared cameras, GIS modeling, and track-count surveys;
* Make the passages wide to accommodate a larger number of species;
* Try to build structures to allow for natural lighting and low noise levels;
* Have a clear view to the other side;
* Use fencing designed to reduce wildlife intrusions;
* Conduct intensive monitoring before and after constructing the wildlife passages via track count surveys, radio-collaring, mark-recapture studies, etc., and;
* Share the results!
It is imperative that biologists and engineers share their findings and ideas concerning crossing structure effectiveness. Events such as the International Conference on Wildlife Ecology and Transportation have become integral to this process. Ideally, the knowledge gained from these meetings will lead to the design of improved crossing structures that will more effectively connect the habitats of a diversity of wildlife.
--- Maureen Hartmann is a graduate student in Environmental Studies at the University of Montana.
Literature Cited
Clevenger, A.P. 1998. Permeability of the Trans-Canada Highway to wildlife in Banff National Park: Importance of crossing structures and factors influencing their effectiveness. Pp.109-119. In G.L. Evink, P.A. Garrett, D. Zeigler, and J. Berry, eds. Proceedings of the International Conference on Wildlife Ecology and Transportation. Feb. 10-12, 1998 Fort Myers, FL. FL DOT FL-ER 69-98.
Clevenger, A.P. and Nigel Waltho. 2000. Factors influencing the effectiveness of wildlife underpasses in Banff National Park, Alberta, Canada. Conservation Biology. 14(1): 47-56.
DeSanto, R.S. and D.G. Smith. 1993. Environmental auditing: An introduction to issues of habitat fragmentation relative to transportation corridors with special reference to high-speed rail (HSR). Environmental Management. 17(1): 111-114.
Gloyne, C.C. and A.P. Clevenger. 2001. Cougar (puma concolor) use of wildlife crossing structures on the Trans Canada highway in Banff National Park, Alberta. Wildlife Biology. 7(2): 117-124.
Groot Bruinderink, G.W.T.A. and E. Hazelbrook. 1996. Ungulate traffic collisions in europe. Conservation Biology. 10(4):1059-1067.
Hunt, A., H.J. Dickens, and R.J. Whelan. 1987. Movement of mammals through tunnels under railway lines. Australian Zoologist. 24(2) 89-93.
Jackson, S.D. and G.R. Curtice. 1998. Toward a practical strategy for mitigating highway impacts on wildlife. Pp. 17-22 in G.L. Evink, P.A. Garrett, D. Zeigler, and J. Berry, eds. Proceedings of the International Conference on Wildlife Ecology and Transportation. Feb. 10-12, 1998 Fort Myers, FL. FL DOT FL-ER 69-98.
Land, D. and M. Lotz. 1996. Wildlife crossing designs and use by florida panthers and other wildlife in southwest Florida. In G.L. Evink, P.A. Garrett, D. Zeigler, and J. Berry, eds. Proceedings of the International Conf. on Wildlife Ecology and Transportation. June, 1996. Tallahassee, FL. FL DOT FL-ER 58-96.
Lavendel, Brian. 2000. Putting the breaks on roadkill. Animals. 133(6):20-23.
Mansergh, I.M., and Scotts, D.J. 1989. Habitat continuity and social organization of the mountain pygmy-possum restored by tunnel. Journal of Wildlife Management. 53(3):701-707.
Rodriguez, A., G. Crema, and M. Delibes. 1996. Use of nonwildlife passages across a high speed railway by terrestrial vertebrates. Journal of Applied Ecology. 33:1527-1540.
Reed, Dale. 1981. Mule deer behavior at a highway underpass exit. Journal of Wildlife Management. 45(2):542-543.
Savage, Candace. 2000. A highway runs through it. Canadian Geographic. 120(5): 35-42.
Scheick, B.K. and M.D. Jones. Locating wildlife underpasses prior to expansion of highway 64 in North Carolina. North Carolina Wildlife Resources Commission, Plymouth and Bridgeton, North Carolina. www.myflorida.com/emo/sched/locate.pdf.
Servheen, C. 2001. U.S. Fish and Wildlife Service Grizzly Bear Recovery Coordinator. Personal Communication Nov, 2001.
Singer, F.J., W.L. Langlitz, and E.C. Samuelson. 1985. Design and construction of highway underpasses used by mountain goats. Transportation Research Record. 1016:6-10.
Sipes, J.L. and J. Neff. 2001. Fencing, wildlife crossings, and roads: separating animals and vehicles. Landscape Architecture. 91(6):24-27.
Whyte Museum. 2000. Mitigation: Reducing the Impacts of Roads and Railways on Bears. http://www.whyte.org/bears/ mitigate.html.
Wilkinson, Todd. Making the road safe ¤ for elk, bears, and wolves. The Christian Science Monitor. 12/09/00. http://www.csmonitor.com/durable/2000/12/19/text/p3sl.html.
Yanes, M., J.M. Velasco, and F. Suarez. 1995. Permeability of roads and railways to vertebrates: The importance of culverts. Biological Conservation. 71:217-222.