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Defenders Magazine
Killer Roads
Roadkill, habitat destruction and fragmentation count among the harms inflict on wildlife.
In my headlights, I saw a rabbit lying in the road, clearly hit by a car. Not an uncommon sight, but the way its ears stood high and its eyes glistened, I knew it was still alive. I slowed down, and as I passed, the animal laid its head against the cold road. When I stopped and returned on foot, it lifted its head to watch me approach.
A car had skidded over the rabbit’s hindquarters. I half- lifted, half-dragged it to the side of the road, to a grassy hollow at the base of a huge live oak. Its blood stained my hands.
Roadkill. We see it nearly every day. It’s part of the landscape as we drive about our daily business. But we never get used to it. The scope of the carnage is beyond what one might imagine: A million animals -- birds, reptiles, mammals and amphibians -- are killed every day by vehicles traveling on America’s roads. Roadkill has edged populations of Florida black bear and panther, federally-endangered ocelot and grizzly bear closer to extinction, and has long surpassed hunting as the primary source of human-caused wildlife mortality in the United States.
"The reason we’re hitting animals is obvious: Our roads are built in their territory, overlaid on the landscape without regard for existing ecological patterns," says Tricia White, transportation associate for Defenders of Wildlife in Washington, D.C. "And with the exception of a handful of endangered species, the direct mortality of animals as a result of vehicle collisions may be the least of the problems that roads inflict on our native wildlife."
Take the Sonoran pronghorn, for example, a unique and elegant North American antelope that once numbered in the millions. Although pronghorn are faring well in many western states, the Sonoran subspecies is on the brink of extinction. Fewer than 100 individuals remain in the United States today. Drastic loss of habitat has confined this species to a small fraction of its natural and necessary range.
The Sonoran pronghorn roadkill is not at significant risk of being killed on a road. Their particular behavioral traits keep them from approaching -- let alone crossing -- roads. But the presence of a road presents a formidable barrier to movement, effectively walling off whatever habitat may exist on the opposite side. This limits the availability of food, water and shelter, impedes dispersal and divides populations into smaller, more isolated units less able to withstand a catastrophe such as disease or fire and more prone to inbreeding and other genetic problems.
Another example is the lynx, a medium-sized cat with long legs and large furry paws -- perfect for hunting in deep snow. Its main food source is the snowshoe hare. Lynxes are cautious and secretive and avoid large open areas. Even when hunting, they prefer some cover and typically won’t cross openings more than 300 feet wide. Clearcuts, ski resorts and mining operations not only destroy huge blocks of habitat but also act as effective barriers to lynxes in their travels. Recreational roads and trails from skiing and snowmobiles allow competitors like coyotes to infiltrate otherwise exclusive lynx habitat and compete for prey.
The degree of impact increases as highways are upgraded from two to four lanes. Highways can also directly affect the amount of feeding and denning habitat available to lynxes by converting natural forests into road surface, rights-of-way or associated facilities such as maintenance areas or gravel pits. In the Adirondack mountains of New York, an attempt to reintroduce lynxes failed, with 18 of 37 mortalities attributed to road kills.
There are now more than 200 million vehicles traveling 5 trillion miles per year in the United States alone. And while roads, bridges and highways allow for the easy transport of people and supplies, they also consume and divide the surrounding mosaic of natural ecosystems. More than 2 percent of the continental United States -- an area the size of Georgia -- is covered by roads and roadsides. This figure doesn’t include parking lots, sidewalks or train and other tracks; in some communities, parking lots now constitute the largest single category of land use. The ecological effects of this development, from noise to direct mortality to vehicle emissions, significantly impact a much larger area.
As the number of roads in an area increases, negative effects on both natural habitats and the species that reside within them escalate. For example, a recent report in California indicates that road construction contributes to the imperilment of 84 of the 286 species listed in the state as threatened or endangered under the federal Endangered Species Act. Habitat fragmentation threatens all wildlife species that have to cross roads to meet their biological needs.
Perhaps the most harmful legacy of roads, though, is that they open up previously undisturbed habitat and open space to more development. Once a road is built, the land alongside it becomes more valuable and more accessible for sprawling new subdivisions and commercial strip malls -- and even more habitat is bound to be lost or fragmented. In urban and suburban landscapes, where humans tend to concentrate their housing and commercial activities, natural habitat is limited and therefore critical to the continuing survival of resident plants and animals. Building roads in these areas not only destroys scarce habitat, it dissects the remaining natural vegetation into increasingly small fragments as well. When this occurs, populations of wildlife species are divided into subpopulations, and movement between them is restricted. These subpopulations are more susceptible to genetic inbreeding and local extinctions due to predators, eventually becoming part of a progressive loss of local biodiversity. For many animals, such as the Sonoran pronghorn, roads act as physical barriers to movement.
Roads take a similar toll on wildlife populations in rural landscapes. Scientists have found that carnivores are more likely to be affected by direct roadkill and interrupted movement through wildlife corridors. "Forest carnivores -- such as wolves, mountain lions, grizzly bears, lynxes and wolverines -- are especially vulnerable," says Bill Ruediger, ecology program leader for highways with the USDA Forest Service, "because of their small populations, low reproduction rates and large home ranges. A male grizzly, for example, requires 200 square miles for its home range."
A case in point is the Florida panther. Only about 50 to 100 individuals remain in south Florida’s Everglades, pushed by decades of unchecked development into a fraction of their historical range. Their remaining habitat is degraded and fragmented. As panthers roam at night to hunt, they are forced to navigate a deadly network of interstate, state and county roads. Cars are the greatest source of panther mortality. In all, seven endangered Florida panthers -- about 8 percent of the entire remaining population -- were killed on highways in 2001, the highest rate in 18 years. Young panthers have nowhere to establish their own territories and are unable to raise families of their own. Without adequate continuous habitat, populations of large, wide-ranging animals such as the Florida panther will eventually disappear.
Roads in forested areas are especially disruptive to the natural flow of groundwater, rivers and fire. Drivers often don’t even realize when they cross streams, nor that the culverts built to carry those streams might pose problems to endangered salmon and trout species. "Most of the culverts in use today were built decades earlier, before scientists understood the needs of the fish that use them," says Ruediger. "In a recent study in northwestern forests, we found that more than a quarter of highways crossing streams and rivers acted as partial or full barriers to young salmon, essentially choking the water flow they need."
Scientists are delving into more and more complex issues regarding wildlife and roads, says Ruediger, but there’s always a new, often unexpected, set of problems to solve.
I stroked the rabbit’s soft, pepper-brown fur, touched its long, sensitive ears, speaking to it quietly. I wanted its suffering to end.
As I crouched beside the road, two cars whooshed past, ruffling my hair and the bunny’s fur, just as I have seen the fur of dead possums parted by the wind in the wake of my own car. How many injured or dead animals have I passed?
Scientists have learned to identify a number of natural wildlife "corridors" that include road crossings, and they are beginning to work with transportation planners to mitigate some of the danger roads can cause to wildlife. In south Florida, the Department of Transportation (DOT) built nearly 30 underpasses in 1993 to allow panthers safe passage under the divided four-lane I-75 highway. DOT also developed and installed a smaller design suited for two-lane highways on State Road 29 north of I-75. So far, no panthers have been killed where crossings are in place, although habitat continuity has not been completely restored. Female panthers are reluctant to cross major roads, even using the underpasses.
Countries such as England, France, Germany, the Netherlands, Switzerland and more recently the United States have been using amphibian tunnels for several decades to facilitate the movement of toads, frogs, newts, spotted salamanders and other species. These animals often cross roads in massive numbers during a brief breeding period to access a pond or wetland. Pipes for small and mid-sized mammals and wildlife overpasses have also been used in Europe for many years and are now becoming more prevalent in the United States.
"Still, you can’t engineer your way out of everything," says Jennifer McMurtray, Defenders’ transportation and wildlife ecology coordinator in Orlando, Florida. "Underpasses can work for some species in specific cases, but will not repair a fragmented landscape for all species of wildlife. We need to look at combining the green and gray infrastructure from the start."
McMurtray is cautiously optimistic about large-scale planning in Florida, citing the existence of a tremendous amount of excellent data that can "help us get a handle on road mortality in this state." For example, researchers in the University of Florida’s landscape ecology program have devised a sophisticated Geographic Information System (GIS) computer model that can capture and manipulate a region’s hydrology, land use, species distribution and existing transportation infrastructure. The model can identify and prioritize roadkill "hot spots" — habitat corridors where collisions are likely to occur. Seventy-two "priority one" road segments and hundreds of lower priority segments have been pinpointed, using criteria such as chronic roadkill sites, biodiversity hot spots, riparian systems, greenway linkages and rare habitat types. Now, university researchers and transportation planners are conducting field studies to evaluate the condition of any existing crossing structures on prioritized segments and recommend needed adaptations.
"We still have at least two big problems to solve regarding road-related mortality in Florida," says McMurtray. "One is that there’s nothing requiring anyone to use this great data we’ve collected. And the other is that Florida is still growing at a phenomenal rate. Sprawl is in the driver’s seat."
Among the hundreds of southeastern myths of the Creek tribe of Indians is one entitled "Man and Rabbit." Here is how it goes:
Rabbit ate some vegetables from a garden, which made the farmer very mad. He started watching the field and soon saw Rabbit follow along the rows, eating peas. The farmer was very angry, and thought, "I will kill him."
When Rabbit saw the man coming he kneeled down beside a big tree, leaning himself against it. The man came up and said, "I am going to kill you, Rabbit, for you have been eating out of my garden." Rabbit answered, "You can kill me, but if you do, you will die also. This tree holds up the earth. With my body, I brace the tree in place. If the tree falls, they say the earth, the sky, and everything will be wiped out and disappear. If you kill me, the earth and the sky together, and all things, will pass away."
The man looked up and saw how the branches of the tree appeared to touch the sky. The sky beyond the tree seemed low to him, as if it were indeed about to fall. When he saw that, the man ran away, leaving Rabbit beside the tree.
For wildlife advocates, perhaps the most far-reaching and effective approach to curbing road-related wildlife mortality will be to join forces with dozens of other organizations bringing the concept of "smart growth" to their communities. Defenders of Wildlife and other groups are joining together on a local, national and international level to combat sprawl. The target is irresponsible development and the dependence on automobiles, a combination that has led to a cycle in which each reinforces the other. In California, a recent National Wildlife Federation report shows that sprawl outranks all other threats to wildlife and contributes to the imperilment of 188 of the 286 species listed as threatened or endangered under the federal Endangered Species Act, or 66 percent of the state’s listed species. Along with wildlife and natural habitats, neighborhood integrity, environmental justice, affordable housing and agricultural lands are also deeply affected by sprawl.
A 2000 national poll by the Washington, D.C.-based Smart Growth America Coalition shows strong public concern about sprawl and indicates that 78 percent of Americans are in favor of smart growth to reduce traffic congestion, preserve existing communities and protect the environment and open space.
"People believe that sprawl and traffic are out of control, and the vast majority want more open space, reliable public transport and neighborhood reinvestment," says Don Chen, director of Smart Growth America.
The state of Maryland is a national leader in smart growth. Landmark 1997 legislation directs significant resources towards a set of smart growth initiatives, and none too soon. In Maryland’s Baltimore–Washington corridor, development has reduced the amount of tree cover from 51 percent to 37 percent in just 25 years, according to a publication released by the Maryland Department of Natural Resources. Thousands of acres of wetlands have also been lost, and the habitat that remains is often so fragmented that it no longer supports diverse wildlife or performs other functions, such as flood control or groundwater replenishment. At the heart of Maryland’s smart growth program is a policy that limits most state infrastructure funding and economic development to areas designated by local governments. In addition, a Rural Legacy Program aims to conserve large areas of agricultural and forested lands, and Program Open Space, in existence since 1969, aims funding at parks and conservation areas. In 2000, Maryland developed a program called "GreenPrint" that uses a green infrastructure assessment completed by the state Department of Natural Resources to identify the forests and wetlands most needed by wildlife so they can be protected by future conservation efforts. The Greenprint program promises to tie together smart growth with conservation using the Rural Legacy Program and Program Open Space as tools. In 1999, Maryland’s Critical Area Commission adopted a forest conservation policy aimed at redirecting development away from the ecologically valuable "critical areas," the 1,000 feet of shoreline next to tidal waters, of the Chesapeake Bay watershed. Incentives to private landowners to keep their land forested and a healthy forest industry are also vital to conservation efforts.
Integrating concepts of smart growth into urban planning and development won’t be easy, conservationists say. Despite strong public support for curbing sprawl, most regions of the country have yet to update antiquated land-use laws and building and zoning codes favoring sprawl to promote more productive land use.
Oregon’s well-known land-use planning program, part of its generally progressive political tradition, sets it well apart from other states in terms of managing sprawl and its effects. Oregon’s land-use program is perhaps best known for its goals to protect farm and forest lands for productive resource use and for its establishment of urban growth boundaries. By containing urban sprawl and protecting large unbroken tracts of agricultural and forested lands, the state provides important benefits for biodiversity and native fish and wildlife habitat. But as Oregon has found, solving sprawl issues isn’t the solution to all of our wildlife’s problems: By concentrating a growing population within a defined urban core, it can become difficult to impossible for animals to move through that densely developed space at all.
Finally, investment in public transit, a key component of smarter growth, falls far behind spending to build new roads at present, even though use of public transportation has grown nearly twice as fast as use of cars since 1996, according to the Smart Growth America poll. Ultimately, efforts to save habitat -- and the species that rely on it -- will depend on the cooperation of all those responsible for land management to identify and protect the most valuable areas.
"We know how roadways impact our wildlife, and we have the information and the technology to avoid and abate these impacts," says Defenders’ Tricia White. "The business of ‘ecologically’ fitting roads to the landscape should be as strong a consideration as traditional engineering and economic factors in future road construction. It’s just a matter of making this issue a priority."
I knew I had to go on to work. I smoothed several twigs from under the rabbit’s body. I bent a thorny vine away from its face. And I drove away. I still feel the sorrow I felt just then, and the helplessness, as well as anger at how we have arranged our lives at the expense of so many animals. In my rearview mirror, as I drove away, I couldn’t help noticing how that dying rabbit seemed to brace the tree it lay against, and the unbroken, wild landscape beyond.
