Overview of Transportation Impacts on Wildlife Movement and Populations
Scott D. JacksonDepartment of Natural Resources Conservation
University of Massachusetts, Amherst
Jackson, S.D. 2000. Overview of Transportation Impacts on Wildlife Movement and Populations. Pp. 7-20 In Messmer, T.A. and B. West, (eds) Wildlife and Highways: Seeking Solutions to an Ecological and Socio-economic Dilemma. The Wildlife Society.
Overview of Transportation Impacts on Wildlife Movement and PopulationsAbstract
As long linear features on the landscape, railways, roads and highways have impacts on wildlife and wildlife habitat that are disproportionate to the area of land that they occupy. In addition to impacts on habitat, highways and railways are sources of road mortality that threaten wildlife populations. Indirect effects on wildlife include reduced access to habitat due to road avoidance and human exploitation. Transportation infrastructure also undermines ecological processes through the fragmentation of wildlife populations, restriction of wildlife movements, and the disruption of gene flow and metapopulation dynamics. A variety of techniques have been used to mitigate the impacts of transportation systems on wildlife movements with mixed success. To make progress on these issues wildlife biologists must: 1) recognize the potential long-term effects of highways and railways on wildlife populations and advocate more strongly for appropriate mitigation measures, 2) document the impacts of transportation infrastructure on wildlife populations, 3) conduct landscape analyses to identify “connectivity zones” and use these analyses to engage transportation planners earlier in the planning process, 4) enlist transportation engineers to help solve technical problems, and 5) design and conduct good monitoring studies to effectively evaluate various mitigation techniques.
Overview of Transportation Impacts on Wildlife Movement and PopulationsImpacts of Highways and Railways on Wildlife
As long linear features on the landscape, railways, roads and highways have impacts on wildlife and wildlife habitat that are disproportionate to the area of land that they occupy. Roads and roadsides cover approximately one percent of the United States, yet it is estimated that 15-20 % of the land is directly affected by roads and vehicles (Forman and Deblinger, 1998; Forman, 2000). With their larger size and higher traffic volumes, highways represent a more serious threat to wildlife, affecting a wider range of wildlife species and presenting an almost impassable barrier for many species of reptiles, amphibians and small mammals.
Roads, highways and railways impact wildlife in a variety of ways.
Direct loss of habitat. Road and railway construction results in changes in the habitat value of the land. Those areas covered by pavement or rails and the travel lanes of dirt or gravel roads are greatly diminished as wildlife habitat. Verges and medians are often intensively managed, though some habitat value persists. Grassy areas associated with highway and roadway alignments represent habitat discontinuities in forested landscapes and may serve as conduits facilitating the spread of undesirable plants and animals (Seabrook and Dettmann, 1996; Parendes and Jones, 2000).
Degradation of habitat quality. Storm water discharges, alterations in stream hydrology, air emissions and exotic plants can degrade habitats ranging up to several hundred meters from railways and highways (for reviews see Transportation Research Board, 1997 and Trombulak and Frissell, 2000).
Habitat fragmentation. Roads, highways and railways dissect continuous habitat patches resulting in smaller patch sizes and higher edge to interior ratios. In forested habitats, edges associated with roads and highways are a source of nest predators and brood parasites that threaten many neotropical forest songbirds (Askins, Philbrick, & Sugeno, 1987; Askins, 1994; Rich, Dobkin, & Niles, 1994). The loss of interior habitat is of concern for edge-sensitive species and smaller overall patch sizes may result in the loss of area-sensitive wildlife.
Road avoidance. Some wildlife species avoid areas adjacent to highways due to noise and human activity associated with roads. Such road avoidance has been documented for black bears, Ursus americanus (Brody and Pelton, 1989), grizzly bears, Ursus arctos (McLellan and Shackleton, 1988), wolves, Canis lupus (Thurber, Peterson, Drummer, & Thomasma, 1994), bobcats, Felis rufus (Lovallo and Anderson, 1996), turkeys, Meleagris gallopavo (McDougal, Vaughan, & Bromley, 1991), and caribou, Rangifer tarandus (Klein, 1979). In the Netherlands, there is evidence that traffic noise disrupts avian communities in both forested and grassland habitats (Reijnen, Foppen, ter Braak, & Thissen, 1995; Reijnen, Foppen, & Meeuwsen, 1996).
Increased human exploitation. Roads and highways increase human access for hunting and poaching. This may reduce wildlife populations in areas adjacent to roads and highways and contributes to road avoidance (Thiel, 1985; McLellan and Shackleton, 1988).
Road mortality leading to loss of populations. When traffic volume is high, small roads can represent a significant source of mortality affecting populations of reptiles and amphibians (van Gelder, 1973; Langton, 1989; Bernardino and Dalrymple, 1992; Patla and Peterson, 1994; Rosen and Lowe, 1994; Fowle, 1996). As individual animals are killed trying to cross a highway or denied access to critical habitats, local populations will likely fail or be substantially reduced. In eastern Texas road mortality may have caused the loss of timber rattlesnake, Crotalus horridus, populations from areas of high road density (Rudolph, Burgdorf, Conner, & Dickson, 1998). Another study of the Angelina National Forest in eastern Texas suggested that populations of large snakes were reduced by 50% or more to a distance of 450 m from roads and concluded that populations of large snakes may be depressed across eastern Texas due to road mortality (Rudolph, Burgdorf, Conner, & Schaefer, 1999). In some cases road mortality has been identified as a important threat affecting endangered species/subspecies such as the Florida Panther, Felis concolor coryi (Maehr, Land, & Roelke, 1991), Old World badger, Meles meles (Zee, Wiertz, Ter Braak, & van Apeldoorn, 1992), and Iberian lynx, Felis pardina (Ferreras, Aldama, Beltran, & Delibes, 1992). The koala, Phascolarctos cinereus, population on Phillip Island, Australia, declined 20 % per year between 1984 and 1991 with road mortality listed as the largest cause of death (Fisher, 1991).
Disruption of social structure. Roads may have decreased survival rates and disrupted social organization for mountain pygmy possums, Burramys parvus, by prohibiting the dispersals of males after the mating season (Mansergh and Scotts, 1989). Studies in the area of Banff National Park in Canada indicate that adult female grizzly bears are much less likely to cross highways than males (Gibeau and Heuer, 1996).
Reduced access to vital habitats. As barriers to wildlife movement, railways and highways reduce access to vital habitats for a variety of wildlife species. Wide-ranging mammal species can lose access to important habitats when movements are restricted by highways. Critical habitats required by wildlife species can be separated on either side a highway, jeopardizing local populations. In Glacier National Park in Montana, mountain goats, Oreamnos americanus, must cross U.S. Highway 2 in order to access an important mineral lick (Singer and Doherty, 1985). Highways have disrupted migrations of ungulates between summer and winter ranges (Klein, 1971; Ward, Cupal, Goodwin, & Morris, 1976; Ford, 1980; Ward, 1982). By separating aquatic habitat and upland nesting habitat for turtles, or terrestrial habitat and aquatic breeding sites for amphibians, highways can have significant adverse impacts on local populations of those species (Jackson, 1996).
Population fragmentation and isolation. Railways and highways create barriers to movement that subdivide animal populations. Local population extinctions may occur due to stochastic genetic and demographic events, environmental variability and natural catastrophes (Shaffer, 1981). Population extinction is more likely to occur in smaller populations, such as those produced by habitat fragmentation (Shaffer, 1981; Shaffer and Samson, 1985). Studies have documented that several species of small mammals are reluctant to cross even relatively small roads (Oxley, Fenton, & Carmody, 1974; Mader, 1984; Swihart and Slade, 1984). DeMaynadier and Hunter (2000) found that salamanders were reluctant to cross forestry roads, with larger and more heavily trafficked roads having the largest impact on movement. The loss of intermediate habitat patches (“stepping stones”) also may contribute to population fragmentation (Trombulak and Frissell, 2000). Smaller and more isolated populations are more vulnerable to genetic changes due to genetic drift and inbreeding depression. Fencing of the Trans Canada Highway has had a significant effect on the movements of grizzly bears and preliminary genetic findings suggest major fractionation of the landscape (Gibeau and Heuer, 1996). Reh and Seitz (1990) found remarkable genetic differences in one population of common frog, Rana temporaria, that was surrounded by roads, a highway and a railway.
Disruption of processes that maintain regional populations. The dispersal of individuals between populations has been shown, based on theoretical grounds (Leigh, 1981; Fahrig and Merriam, 1985; Hanski and Gilpin, 1991; Beier, 1993) and field studies (Gill, 1978; Corn and Fogleman, 1984; Breden, 1987; Berven and Grudzien, 1990; Sjogren, 1991), to be important for the maintenance of genetic viability within local populations, and for maintaining local and regional populations in the face of population extinctions. Dispersal among local populations is important for maintaining gene flow, supplementing small or declining populations, and re-colonizing local populations lost to extinction events. Effects of habitat fragmentation on metapopulation dynamics (Dodd, 1990; Beier, 1993; Gibbs, 1993; Blaustein, Wake, & Sousa, 1994; Fahrig and Merriam, 1994) and specifically, the impacts of roads and highways on local and regional populations (Mader, 1984; Andrews, 1990; Reh and Seitz, 1990; Patla and Peterson, 1994; Vos and Chardon, 1998) are important factors affecting the long-term persistence of populations. As barriers to animal dispersal, highways constitute an important long-term threat to the maintenance of healthy wildlife populations.
The combined effects of transportation infrastructure – habitat loss and degradation, habitat fragmentation, road mortality, and the restriction of animal movement across the landscape – are likely to have serious consequences for wildlife populations over time. Studies in Canada indicate a correlation between traffic intensity and lower densities of calling anurans (Fahrig, Pedlar, Pope, Taylor, & Wegner, 1995) and between the density of paved roads within 1-2 km of wetlands and the diversity of wildlife in those wetlands (Findlay and Houlahan, 1997; Findlay and Bourdages, 2000). Population level impacts are hard to document and may not be readily apparent until years or decades have passed (Findlay and Bourdages, 2000). Harder still is the assessment of long-term effects from the disruption of metapopulation dynamics and differential impacts of transportation infrastructure on animal movements. Wildlife species are not all affected to the same degree by the barrier effects of road, highways and railways. These habitat barriers may act as "filters" that stop some individuals and allow others to pass through. By "filtering out" different species, habitat barriers can have important impacts on species distribution across fragmented landscapes (Kozakiewicz, 1993).
For additional summaries of highway and railway effects on wildlife, including effects of habitat fragmentation, see Andrews (1990), Bennett (1991), De Santo and Smith (1993), and Trombulak and Frissell (2000).
Mitigating Impacts of Roads, Highways and Railways on Wildlife Movements
Many mitigation projects are primarily designed to facilitate movements of a single species or small group of similar species. Public safety, protection of big game, and the conservation of particular populations of wildlife (including rare or endangered species) are the primary motivating forces behind mitigation projects. Little attention is being paid to the role of highway mitigation in maintaining overall landscape connectivity in the U.S., although attempts to construct wildlife passage systems for a broad range of species are being tried in Europe (Canters, 1997) and Canada (Leeson, 1998).
In North America most mitigation projects are designed to facilitate the movements of large mammals. Most are designed for ungulates (Reed, Woodard, & Pojar, 1975; Ward et al., 1976; Ford, 1980; Singer and Doherty, 1985; Romin and Bissonette, 1996). Exceptions include underpasses for Florida panthers (Foster and Humphrey, 1995; Land & Lotz, 1996) and black bears (Roof & Wooding, 1996) in Florida; amphibian tunnels in Massachusetts (Jackson and Tyning, 1989; Jackson, 1996), New York (M. Fitzsimmons, pers comm.) and California (H.B. Shaffer, email post); a wall with passage structures for reptiles and amphibians in Florida (Evink, 1998); and a proposal for 13 crocodile, Crocodylus acutus, underpasses in the Florida Keys (Evink, 1996). Mitigation projects for two federally listed species, the Houston toad, Bufo houstonensis, (Jenkins, 1996) and Desert Tortoise, Gopherus agassizii, (Boarman and Sazaki, 1996) utilized existing drainage culverts rather than underpasses specifically designed to meet the particular needs of these species.
Tunnels have been used to help facilitate the movement of wildlife across roads and highways in Europe, Australia, Canada and the U.S. Evaluations of the effectiveness of tunnels indicate the need for careful design and placement, and that effectiveness is dependent on a number of variables, including: size, placement, noise levels, substrate, vegetative cover, moisture, temperature and light (Jackson and Griffin, 1998). More recently, overpass structures, also called ecoducts or green bridges, have been used to facilitate passage for a wide range of species (Berris, 1997; Keller and Pfister, 1997). These large overpass systems for wildlife appear to the most effective design for accommodating the needs of a broad range of wildlife species.
Current and Future Issues and Challenges
Much progress has been made in the past several years in understanding the impacts of transportation infrastructure on wildlife and developing techniques and approaches for mitigated those impacts. To continue making progress on these issues wildlife biologists will need to address the following challenges.
Fostering Greater Appreciation of the Problems Caused by Highways and Railways. One important challenge is getting people to understand the scope and complexity of transportation impacts on wildlife. Too often the issue is viewed as one of an incidental take of animals rather than as a threat to wildlife populations. We must seek to frame the issue not as concern for individual animals but rather that of maintaining the ecological integrity of natural systems intersected by railways and highways. The movement of animals through the landscape is one of many ecological processes that must be maintained in order to insure the integrity of ecosystems over time. The impacts of railways and highways do not simply occur at the time of construction but accumulate over time as populations fail due to transportation impacts and pathways for re-colonization are precluded (Findlay and Bourdages, 2000). Appropriate planning and mitigation at the time of construction can go a long way in preventing long-term degradation of wildlife populations and the ecosystems in which wildlife are important components.
Documenting the Impacts of Transportation Infrastructure on Wildlife Populations. There is a growing body of research into the ways that roads, highways and railways impact wildlife movements and populations. However, the extent to which these features are affecting wildlife populations and undermining ecological processes is still largely unknown. Further research is needed on the long-terms effects of transportation infrastructure as well as the nature and extent of impacts for a broader range of wildlife species.
Landscape Analyses to Identify “Connectivity Zones”. The most effective techniques for facilitating wildlife movement (overpasses, viaducts, and large underpasses) are also quite expensive. Therefore, it is generally not practical to make entire highways or railways permeable to wildlife movement. A practical strategy for mitigating transportation impacts on wildlife movement may dictate that comprehensive efforts utilizing expensive elements be reserved for areas that are identified and designated as important travel corridors or connections between areas of significant habitats (Jackson and Griffin, 1998). These landscape analyses are common in Europe (see Canters, 1997) and there are some notable examples from North America (Wagner, Carey, & Lehmkuhl, 1998; Carr, Zwick, Hoctor, Harrell, Goethals, & Benedict, 1998; Smith, 1999; Hoctor, Carr, & Zwick, 2000). To the extent that these areas can be identified ahead of time, planning for new transportation infrastructure can more effectively focused on minimizing and mitigating impacts to these critical areas.
Enlisting Transportation Engineers to Help Solve Technical Problems. There still is much work to be done in designing wildlife crossing structures that are effective for facilitating animal passage and practical for use in transportation systems. Biologists need to establish the performance standards for such structures based on the characteristics and needs of wildlife. The assistance of transportation engineers is needed to provide technical solutions and approaches so that crossing structures more effectively meet the standards identified by biologists. An example of a problem in need of a technical solution is how best to provide a wet environment within crossing structures to facilitate amphibian use during migration. Given the incredible feats of engineering accomplished over the years by transportation engineers, collaborative partnerships between biologists and engineers should be able to find practical solutions to many technical problems related to animal passage.
Monitoring and Evaluation of Wildlife Crossing Structures. Monitoring studies that evaluate the effectiveness of wildlife crossing structures have provided valuable information that is now available for use in designing future mitigation. As new structures are built it is particularly important that these efforts be monitored and the lessons learned from these mitigation experiments shared with others.
Most attempts to evaluate the success or failure of wildlife crossing structures have focused on documenting wildlife use of structures. Use of tracking beds, cameras, and counters do provide information about animals that use the structures. Unfortunately, monitoring structure use provides little information on species or individuals that fail or refuse to use the structure. Radio-tracking and trapping studies provide less information about structure use, but are more useful for determining the extent to which railways and highways inhibit wildlife movement and the degree to which crossing structures are able to mitigate these effects. In order to fully assess the effectiveness of wildlife crossing structures it may be necessary to use a combination of techniques that will evaluate both structure use and the degree to which railway or highway effects on animal movement are mitigated.Conclusion
There is good reason for concern that roads, highways and railways are having a profound affect on wildlife populations and ecosystems, especially if considered at the landscape scale and over long time frames. Although progress has been made in recognizing and addressing these impacts, many challenges persist. There is a need for a significantly different approach to transportation planning, one that recognizes the long-term ecological costs of roads, highways and railways, and takes seriously the need to mitigate these impacts.
Acknowledgement
Funding for much of the research used in this paper came from the U.S. Environmental Protection Agency. Special thanks to Peter Oggier, Carme Rosell, and Carolyn Callahan, who hosted visits abroad to learn from projects in their countries. Thanks also go to the many people who took the time to meet with us and share their experiences with highway impacts and mitigation projects: Bruce Leeson, Andrew Eller, Dale Becker, Mark Lotz, Annette Piepers, Jeroen Brandjes, Pauline Schakenbos, Daniela Heynen, Stephen Gniadeck, and Mark Kern.
References Cited
Andrews, A. 1990. Fragmentation of habitat by roads and utility corridors: a review. Aust. Zool. 26(3&4):130-141.
Askins, R.A. 1994. Open corridors in a heavily forested landscape: impact on shrubland and forest-interior birds. Wildl. Soc. Bull. 22:339—347.
Askins, R.A., M.J. Philbrick, and D.S. Sugeno. 1987. Relationship between the regional abundance of forest and the composition of forest bird communities. Biol. Conserv. 39:129-152.
Beier, P. 1993. Determining minimum habitat areas and habitat corridors for cougars. Cons. Biol. 7(1):94-108.
Beier, P. 1995. Dispersal of juvenile cougars in fragmented habitat. J. Wildl. Manage. 59(2):228-237.
Bennett, A.F. 1991. Roads, roadsides, and wildlife conservation: a review. Pp. 99-118 In D.A. Saunders and R.J. Hobbs (eds.) Nature Conservation 2: The Role of Corridors. Surrey Beatty & Sons, London.
Bernardino, F.S., Jr. and G.J. Dalrymple. 1992. Seasonal activity and road mortality of the snakes of the Pa-hay-okee wetlands of Everglades National Park, USA. Biol. Conserv. 62:71-75.
Berris, L. 1997. The importance of the ecoduct at Terlet for migrating mammals. 1997. pp. 418-420 In K. Canters (ed.) Habitat Fragmentation & Infrastructure, proceedings of the international conference on habitat fragmentation, infrastructure and the role of ecological engineering. Ministry of Transport, Public Works and Water Management, Delft, The Netherlands.
Berven, K. A. and T. A. Grudzien. 1990. Dispersal in the wood frog (Rana sylvatica): implications for genetic population structure. Evolution 44:2047-2056.
Blaustein, A.R., D.B. Wake and W.P. Sousa. 1994. Amphibian declines: judging stability, persistence, and susceptibility of populations to local and global extinctions. Cons. Biol. 8(1):60-71.
Boarman, W.I. and M. Sazaki. 1996. Highway mortality in desert tortoises and small vertebrates: success of barrier fences and culverts. 5 pp. In G.L. Evink, P. Garrett, D. Zeigler and J. Berry (eds.) Trends in Addressing Transportation Related Wildlife Mortality, proceedings of the transportation related wildlife mortality seminar. State of Florida Department of Transportation, Tallahassee, FL. FL-ER-58-96.
Breden, F. 1987. The effect of post-metamorphic dispersal on the population genetic structure of Fowler's toad, Bufo woodhousii fowleri. Copeia 1987:386-395.
Brody A.J. and M.R. Pelton. 1989. Effects of roads on black bear movements in western North Carolina. Wildl. Soc. Bull 17:5-10.
Canters, K. (ed.). 1997. Habitat fragmentation and Infrastructure: Proceedings of the International Conference on Habitat Fragmentation, Infrastructure and the Role of Ecological Engineering. Ministry of Transport, Public Works and Water Management, Delft, The Netherlands. 474 pp.
Carr, M.H., P.D. Zwick, T. Hoctor, W. Harrell, A. Goethals, and M. Benedict. 1998. Using GIS for identifying the interface between ecological greenways and roadway systems at the state and sub-state scales. Pp. 68-77 In G.L. Evink, P. Garrett, D. Zeigler, and J. Berry (eds.) Proceedings of the International Conference on Wildlife Ecology and Transportation. FL-ER-69-98. Florida Department of Transportation, Tallahassee, Florida.
Corn, P.S. and J.C. Fogleman. 1984. Extinction of montane populations of the northern leopard frog (Rana pipiens) in Colorado. J. Herpetol. 18(2):147-152.
DeMaynadier, P.G. and M.L. Hunter. 2000. Road effects on amphibian movements in a forested landscape. Natural Areas Journal 20:56-65.
De Santo, 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 17:111-114.
Dodd, C. K. 1990. Effects of habitat fragmentation on a stream dwelling species, the flattened musk turtle Sternotherus depressus. Biol. Conserv. 54:33-45.
Evink, G.L. 1996. Florida Department of Transportation initiatives related to wildlife mortality. 9 pp. In G.L. Evink, P. Garrett, D. Zeigler and J. Berry (eds.) Trends in Addressing Transportation Related Wildlife Mortality, proceedings of the transportation related wildlife mortality seminar. State of Florida Department of Transportation, Tallahassee, FL. FL-ER-58-96.
Evink, G.L. 1998. Moving forward. Pp. 7-9. In G.L. Evink, P. Garrett, D. Zeigler, and J. Berry (eds.) Proceedings of the International Conference on Wildlife Ecology and Transportation. FL-ER-69-98. Florida Department of Transportation, Tallahassee, Florida.
Fahrig L. and G. Merriam. 1985. Habitat patch connectivity and population survival. Ecology 66(6):1762-1768.
Fahrig L. and G. Merriam. 1994. Conservation of fragmented populations. Cons. Biol. 8(1):50-59.
Fahrig L., J.H. Pedlar, S. Pope, P.D. Taylor and J.F. Wegner. 1995. Effect of road traffic on amphibian density. Biol. Cons. 73:177-182.
Ferreras, P., J.J. Aldama, J.F. Beltran and M . Delibes. 1992. Rates and causes of mortality in a fragmented population of Iberian lynx Felis pardina Temminck, 1824. Biol. Cons. 61:197-202.
Findlay, C.S. and J. Bourdages. 2000. Response time of wetland biodiversity to road construction on adjacent lands. Cons. Biol. 14(1):86-94.
Findlay, C.S. and J. Houlahan. 1997. Anthropogenic correlates of species richness in Southeastern Ontario wetlands. Cons. Biol. 11:1000-1009.Forman, R.T.T. 2000. Estimate of the area affected ecologically by the road system in the United States. Cons. Biol. 14(1):31-35.
Fisher, J. 1991. A strategy plan for koalas on Phillip Island. Pp. 54-64. In Koalas at Risk. Phillip Island Friends of the Koalas, Inc. Cowes, Victoria, Australia.
Ford, S.G. 1980. Evaluation of highway deer kill mitigation on SIE/LAS-395. U.S. Department of Transportation Report No. FHWA/CA/TP-80/01.
Forman, R.T.T. 2000. Estimate of the area affected ecologically by the road system in the United States. Cons. Biol. 14(1):31-35.
Forman, R.T.T and R.D. Deblinger. 1998. The Ecological Road-Effect Zone for Transportation Planning and Massachusetts Highway Example. Pp. 78-96. In G.L. Evink, P. Garrett, D. Zeigler, and J. Berry (eds.) Proceedings of the International Conference on Wildlife Ecology and Transportation. FL-ER-69-98. Florida Department of Transportation, Tallahassee, Florida.
Foster, M.L. and S.R. Humphrey. 1995. Use of highway underpasses by Florida panthers and other wildlife. Wildl. Soc. Bull. 23(1):95-100.
Fowle, S.C. 1996. Effects of roadkill mortality on the western painted turtle (Chrysemys picta bellii). 14 pp. In G.L. Evink, P. Garrett, D. Zeigler and J. Berry (eds.) Trends in Addressing Transportation Related Wildlife Mortality, proceedings of the transportation related wildlife mortality seminar. State of Florida Department of Transportation, Tallahassee, FL. FL-ER-58-96.
Gibeau, M.L. and K. Heuer. 1996. Effects of transportation corridors on large carnivores in the Bow River Valley, Alberta. 13 pp. In G.L. Evink, P. Garrett, D. Zeigler and J. Berry (eds.) Trends in Addressing Transportation Related Wildlife Mortality, proceedings of the transportation related wildlife mortality seminar. State of Florida Department of Transportation, Tallahassee, FL. FL-ER-58-96.
Gibbs, J.P. 1993. Importance of small wetlands for the persistence of local populations of wetland-associated animals. Wetlands 13(1):25-31.
Gill, D.E. 1978. The metapopulation ecology of the red-spotted newt, Notophthalmus viridescens (Rafinesque). Ecological Monographs 48:145-166.
Hanski, I. and M.E. Gilpin. 1991. Metapopulation dynamics: brief history and conceptual domain. Biological Journal of the Linnean Society 42:3-16.
Hoctor, T.S., M.H. Carr, and P.D. Zwick. 2000. Identifying a linked reserve system using a regional landscape approach: the Florida Ecological Network. Cons. Biol. 14(4):984-1000.
Jackson, S.D. 1996. Underpass systems for amphibians. 4 pp. In G.L. Evink, P. Garrett, D. Zeigler and J. Berry (eds.) Trends in Addressing Transportation Related Wildlife Mortality, proceedings of the transportation related wildlife mortality seminar. State of Florida Department of Transportation, Tallahassee, FL. FL-ER-58-96.
Jackson, S.D. and C.R. Griffin. 1998. Toward a practical strategy for mitigating highway impacts on wildlife. Pp. 17-22 In G.L. Evink, P. Garrett, D. Zeigler, and J. Berry (eds.) Proceedings of the International Conference on Wildlife Ecology and Transportation. FL-ER-69-98. Florida Department of Transportation, Tallahassee, Florida.
Jackson, S.D. and T.F. Tyning. 1989. Effectiveness of drift fences and tunnels for moving spotted salamanders Ambystoma maculatum under roads. Pp. 93-99 In T.E.S. Langton (ed.) Amphibians and Roads, proceedings of the toad tunnel conference. ACO Polymer Products, Shefford, England.
Jenkins, K. 1996. Texas Department of Transportation wildlife activities. 31 pp. In G.L. Evink, P. Garrett, D. Zeigler and J. Berry (eds.) Trends in Addressing Transportation Related Wildlife Mortality, proceedings of the transportation related wildlife mortality seminar. State of Florida Department of Transportation, Tallahassee, FL. FL-ER-58-96.
Keller, V. and H.P. Pfister. 1997. Wildlife passages as a means of mitigating effects of habitat fragmentation by roads and railway lines. pp. 70-80 In K. Canters (ed.) Habitat Fragmentation & Infrastructure, proceedings of the international conference on habitat fragmentation, infrastructure and the role of ecological engineering. Ministry of Transport, Public Works and Water Management, Delft, The Netherlands.
Klein, D.R. 1971. Reaction of reindeer to obstructions and disturbances. Science 174:393-398.
Klein, D.R. 1979. The Alaska Oil Pipeline in Retrospect. Trans North American Wildlife and Natural Resource Conference 44:235-246.
Kozakiewicz, M. 1993. Habitat isolation and ecological barriers – the effect on small mammal populations and communities. Acta Theriol. 38:1-30.
Land, D. and M. Lotz. 1996. Wildlife crossing designs and use by Florida panthers and other wildlife in Southwest Florida. 6 pp. In G.L. Evink, P. Garrett, D. Zeigler and J. Berry (eds.) Trends in Addressing Transportation Related Wildlife Mortality, proceedings of the transportation related wildlife mortality seminar. State of Florida Department of Transportation, Tallahassee, FL. FL-ER-58-96.
Langton, T.E.S. 1989. Tunnels and temperature: results from a study of a drift fence and tunnel system at Henley-on-Thames, Buckinghamshire, England. Pp. 145-152 In T.E.S. Langton (ed.) Amphibians and Roads, proceedings of the toad tunnel conference. ACO Polymer Products, Shefford, England.
Leeson, B.F. 1998. Bridging the Rockies – Banff’s roadways for wildlife. P. 120 In G.L. Evink, P. Garrett, D. Zeigler, and J. Berry (eds.) Proceedings of the International Conference on Wildlife Ecology and Transportation. FL-ER-69-98. Florida Department of Transportation, Tallahassee, Florida.
Leigh, E.G., Jr. 1981. The average lifetime of a populations in a varying environment. J. Theor. Biol. 90:213-239.
Lovallo, M.J. and E.M. Anderson. 1996. Bobcat movements and home ranges relative to roads in Wisconsin. Wildl. Soc. Bull 24:71-76.
Mader, H.J. 1984. Animal habitat isolation by roads and agricultural fields. Biol. Conserv. 29:81-96.Maehr, D.S., E.D. Land and M.E. Roelke. 1991. Mortality patterns of panthers in southwest Florida. Proc. Annu. Conf. of Southeast. Assoc. Fish and Wildl. Agencies 45:201-207.
Maehr, D.S., E.D. Land and M.E. Roelke. 1991. Mortality patterns of panthers in southwest Florida. Proc. Annu. Conf. of Southeast. Assoc. Fish and Wildl. Agencies 45:201-207.
Mansergh, I.M. and D.J. Scotts. 1989. Habitat continuity and social organization of the Mountain Pygmy-possum restored by tunnel. J. Wildl. Manage. 53(3):701-707.
McDougal, L.A., M.R. Vaughan, and P.T. Bromley. 1991. Wild turkey and road relationships on a Virginia National Forest. Pp. 96-106. In W.M. Healy and G.B. Healy (eds.) Proceedings of the Sixth National Wild Turkey Symposium. National Wild Turkey Federation. Edgefield, South Carolina.
McLellan, B.N. and D.M. Shackleton. 1988. Grizzly bears and resource-extraction industries: effects of roads on behavior, habitat use and demography. J. Appl. Ecol. 25:451-460.
Oxley, D.J., M.B. Fenton and G.R. Carmody. 1974. The effects of roads on populations of small mammals. J. Appl. Ecol. 11:51-59.
Parendes, L.A. and J.A. Jones. 2000. Role of light availability and dispersal in exotic plant invasion along roads and streams in the H. J. Andrews Experimental Forest, Oregon. Cons. Biol. 14(1):64-75.
Patla, D.A. and C.R. Peterson. 1994. The effects of habitat modification on a spotted frog population in Yellowstone National Park. Unpublished report to the University of Wyoming National Park Service Research Center. 11+6 pp.
Reed, D.F., T.N. Woodard and T.M. Pojar. 1975. Behavioral response of mule deer to a highway underpass. J. Wildl. Manage 39(2):361-367.
Reh, W. and A. Seitz. 1990. The influence of land use on the genetic structure of populations of the common frog Rana temporaria. Biol. Conserv. 54:239-249.
Reijnen, R., R. Foppen, C. ter Braak, and J. Thissen. 1995. The effects of car traffic on breeding bird populations in woodland. III. Reduction of density in relation to proximity of main roads. J. Appl. Ecol. 32:187-202.
Reijnen, R., R. Foppen, and H. Meeuwsen. 1996. The effects of car traffic on the density of breeding birds in Dutch agricultural grasslands. Biol. Conserv. 75:255-260.
Rich, A.C., D.S. Dobkin, and L.J. Niles. 1994. Defining forest fragmentation by corridor width: the influence of narrow forest-dividing corridors on forest-nesting birds in southern New Jersey. Cons. Biol. 8(4):1109-1121.
Romin, L.A. and J.A. Bissonette. 1996. Deer-vehicle collisions: status of state monitoring activities and mitigation efforts. Wildl. Soc. Bull. 24(2):276-283.
Roof, J. and J. Wooding. 1996. Evaluation of the S.R. 46 wildlife crossing in Lake County, Florida. 7 pp. In G.L. Evink, P. Garrett, D. Zeigler and J. Berry (eds.) Trends in Addressing Transportation Related Wildlife Mortality, proceedings of the transportation related wildlife mortality seminar. State of Florida Department of Transportation, Tallahassee, FL. FL-ER-58-96.
Rosen, P.C. and C.H. Lowe. (1994). Highway mortality of snakes in the Sonoran Desert of southern Arizona. Biol. Conserv. 68:143-148.
Rudolph, D.C., S. Burgdorf, R.N. Conner, and J.G. Dickson. 1998. The impact of roads on the timber rattlesnake (Crotalus horridus), in eastern Texas. Pp. 236-240 In G.L. Evink, P. Garrett, D. Zeigler, and J. Berry (eds.) Proceedings of the International Conference on Wildlife Ecology and Transportation. FL-ER-69-98. Florida Department of Transportation, Tallahassee, Florida.
Rudolph, D.C., S. Burgdorf, R.N. Conner, and R. Schaefer. 1999. Preliminary evaluation of the impact of roads and associated vehicular traffic on snake populations in eastern Texas. Pp. 129-136 In G.L. Evink, P. Garrett, and D. Zeigler (eds.) Proceedings of the Third International Conference on Wildlife Ecology and Transportation. FL-ER-73-99. Florida Department of Transportation, Tallahassee, Florida.
Seabrook, W.A. and E.B. Dettmann. 1996. Roads as activity corridors for cane toads in Australia. J. Wildl. Manage 60:363-368.
Shaffer, M.L. 1981. Minimum population sizes for species conservation. BioScience 31(2):131-134.
Shaffer, M.L. and F.B. Samson. 1985. Population size and extinction: a note on determining critical population sizes. Am. Nat. 125:144-152.
Singer, F.J. and J.L. Doherty. 1985. Managing mountain goats at a highway crossing. Wild. Soc. Bull. 13:469-477.
Sjogren, P. 1991. Extinction and isolation gradients in metapopulations: the case of the pool frog (Rana lessonae). Biological Journal of the Linnean Society 42:135-147.
Smith, D.J. 1999. Identification and prioritization of ecological interface zones on state highways in Florida. Pp. 209-229 In G.L. Evink, P. Garrett, and D. Zeigler (eds.) Proceedings of the Third International Conference on Wildlife Ecology and Transportation. FL-ER-73-99. Florida Department of Transportation, Tallahassee, Florida.
Swihart, R.K. and N.A. Slade. 1984. Road crossing in Sigmodon hispidus and Microtus ochrogaster. J. Mamm. 65(2):357-360.
Thiel, R.P. 1985. Relationship between road densities and wolf habitat suitability in Wisconsin. Am. Midl. Nat. 113:404-407.
Thurber, J.M., R.O. Peterson, T.D. Drummer, and S.A. Thomasma. 1994. Gray wolf response to refuge boundaries and roads in Alaska. Wildl. Soc. Bull. 22:61-67.
Transportation Research Board. 1997. Toward a Sustainable Future: Addressing the long-term effects of motor vehicle transportation on climate and ecology. National Research Council Special Report #251. 261 + xiv pp.
Trombulak S.C. and C.A. Frissell. 2000. Review of ecological effects of roads on terrestrial and aquatic communities. Cons. Biol. 14(1):18-30.
van Gelder, J.J. 1973. A Quantitative approach to the mortality resulting from traffic in a population of Bufo bufo L. Oecologia (Berl.) 13:93-95.
Vos, C.C. and J.P. Chardon. 1998. Effects of habitat fragmentation and road density on the distribution pattern of the moor frog Rana arvalis. J. Appl. Ecol. 35:44-56.
Wagner, P., M. Carey, and J. Lehmkuhl. 1998. Assessing habitat connectivity through transportation corridors on a broad scale: an interagency approach. Pp. 66-67 In G.L. Evink, P. Garrett, D. Zeigler, and J. Berry (eds.) Proceedings of the International Conference on Wildlife Ecology and Transportation. FL-ER-69-98. Florida Department of Transportation, Tallahassee, Florida.
Ward, A.L. 1982. Mule deer behavior in relation to fencing and underpasses on Interstate 80 in Wyoming. Transportation Research Record 859, pp. 8-13.
Ward, A.L., J.J. Cupal, G.A. Goodwin, and H.D. Morris. 1976. Effects of highway construction and use on big game populations. U.S. Department of Transportation, Federal Highway Administration. Springfield, VA. 98 pp.
Zee, F.F. van der, J. Wiertz, C.J.F Ter Braak, R.C. van Apeldoorn. 1992. Landscape change as a possible cause of the badger Meles meles L. decline in The Netherlands. Biol. Conserv. 61:17-22.