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Linking Habitats and Reducing Roadkill
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Wide-ranging large carnivores,
such as grizzly bears and wolves, and slow-moving animals, such as salamanders
and turtles, are particularly vulnerable to becoming roadkill. Photo Credit: Chuck Bartlebaugh |
Wildlife and Highways: An Overview
About 6.3 million kilometers (almost 4 million miles) of public roads crisscross
the United States. Wildlife experts say these roads affect animals in several
ways: roadkill, habitat loss, and habitat fragmentation.
Roadkill
Millions of animals - birds, reptiles, mammals, and amphibians - are killed
every year by vehicles traveling on America's roads. For example, partially
as a result of roadkills, the population of an endangered cat - the ocelot -
has been reduced to about 80 animals.
Slow-moving animals, such as turtles and salamanders, are at high risk of becoming
roadkill, especially when they try to cross a road to reach mating or nesting
sites on the other side.
Wide-ranging, large carnivores, such as wolves, grizzly bears, and mountain
lions are also vulnerable, simply because they routinely have to cross many
roads.
Animals on roads are a risk to humans as well. Each year, more than 200 motorists
are killed and thousands more are injured in animal-vehicle collisions, according
to The Wildlife Society. The insurance industry estimates that the annual cost
to society for these fatalities and injuries is $200 million. Individual motorists
usually pay at least $2,000 for vehicle repair every time they hit a large animal.
Habitat Loss
Over the centuries, the habitat lost to wildlife has resulted not only from
highway construction but also from timber harvesting, agricultural conversion,
urban and residential development, and other factors.
Loss of habitat is permanent and severe. For example, the threatened grizzly
bear is now confined to less than 2 percent of its former range south of Canada,
and only two robust populations remain of the rare lynx that once prowled forested
areas from Maine to Oregon.
The red-legged frog, which is on the federal endangered species list, has disappeared
from 99 percent of its habitat in California's Central Valley. Another endangered
amphibian in California, the Arroyo toad, can be found only in remote areas
of the state. Still another wildlife species, Atwater's greater prairie chicken,
is down to three isolated populations (42 animals) in Texas. The list goes on.
Habitat Fragmentation
Few species use all the patches of a landscape. Their survival depends on being
able to move from one patch to another. Highways "fragment" landscapes
and divide wildlife populations into smaller, more isolated units. Smaller populations
are less stable. Over time, they may face extinction from predators or natural
causes, and they may also be more susceptible to inbreeding and genetic defects.
Habitat fragmentation threatens all wildlife species that have to cross roads
to meet their biological needs. "Forest carnivores are particularly vulnerable,"
says biologist Bill Ruediger of the U.S. Forest Service. "They're at risk
because of their small populations, low reproduction rates, and large - even
huge - home ranges."
In 1987, two tunnels
were built in Amherst, Mass., to help salamanders migrate to and from the
warm, fishless vernal pools (small temporary ponds) where they migrate every
spring to mate and lay eggs. Two spotted salamanders, glossy black with
two rows of bright yellow spots down their backs and tails, crawl safely
through one of the tunnels under the highway. Photo Credit: Scott Jackson |
An Uphill Climb for Fish
The effects on fish populations are less obvious. We drive over culverts without
even realizing there are streams underneath. Even if we can see a stream, we
usually can't see the fish swimming in the water. Nonetheless, the impacts are
real and serious.
Anadromous fish - species that migrate from freshwater to saltwater and back
to freshwater - are most severely affected by fish barriers. Most of the culverts
we drive over today were built decades ago before we knew about the needs of
these species.
Ability to migrate upstream is the critical issue for both anadromous and resident
fish species. "Juveniles have a tougher time than adults," says Rose
Owens, a biologist at the Oregon Department of Transportation. "They can't
jump as high or sustain the same bursts of energy, and they're more sensitive
than adults to turbulence and to changes in water temperature."
In the Pacific Northwest, the fish-passage issue is complicated by biology.
Pacific salmon, unlike Atlantic salmon, exist as several species. Different
populations spawn at different times and in different streams. What's more,
Pacific salmon spawn only once and then die.
Fish populations in the Pacific Northwest have been steadily declining - not
only because of transportation-linked barriers to upstream movement but also
because of dams, pollution, over-harvesting, and other human disturbances. Populations
have declined to such an extent that virtually all stocks of wild salmon and
trout are federally listed in some region of the Pacific Northwest. For example,
Chinook salmon stocks are federally listed in Puget Sound, in the Columbia and
Sacramento Rivers, and in other watersheds.
Opportunities to Make
a Difference
Under the Transportation Equity Act for the 21st Century (TEA-21), FHWA funding
is available for wildlife crossings on both new and existing roads. Thanks to
TEA-21 and an expanded "Transportation Enhancements" category, states
and communities can get help not only for crossing structures but also for habitat
connectivity measures.
"President Clinton has made protecting the environment one of his top priorities,"
said Federal Highway Administrator Kenneth R. Wykle. "TEA-21 offers an
unprecedented opportunity for us to reduce highway impacts on wildlife."
Several strategies are being used to counteract roadkill, habitat loss, and
fragmentation. The strategies range from site-specific projects, such as salamander
tunnels and bear underpasses, to regional models that combine landscape ecology,
conservation biology, and human safety concerns with long-range transportation
planning.
For more information about "Critter Crossings," contact Paul Garrett at (303) 969-5772 or Paul.Garrett@fhwa.dot.gov. The full text of CRITTER CROSSINGS: Linking Habitats and Reducing Roadkill, is available on the FHWA Web site at www.fhwa.dot.gov/environmentwildlifecrossings/".
CRITTER CROSSINGS: Linking Habitats and Reducing Roadkill was written by Ginny Finch, who is a program analyst in FHWA's Office of Natural Environment. Her other brochures include More Than Asphalt, Concrete, and Steel; Leaving A Place Better Than You Found It; Wetlands and Highways; and Environmental Research: Linking Transportation, the Environment, and the Future.
Bear Underpasses in Florida When biologists and
engineers from the Florida Department of Transportation (FDOT) and the
Florida Fish and Wildlife Conservation Commission (FWC) designed the state's
first underpass for black bears on a stretch of state Route 46 in Lake
County, they had done their homework. They noted that bears had been using
similar crossings built for Florida panthers on Alligator Alley (now I-75).
They also observed bears routinely traveled across the targeted section
of state Route 46 near County Road 433 to get to habitats within central
Florida's Wekiva River Basin. And they learned bears were being hit by
vehicles more often at this spot on SR 46 than at any other spot on the
highway. For more information, contact Terry Gilbert at (850) 488-6661 or gilberd@gfc.state.fl.us. |
Studying Wildlife
Linkage Areas in Washington State
The Northwest Forest
Plan calls the Snoqualmie Pass/Interstate 90 corridor east of Seattle
"a critical connective link in the north-south movement of organisms
in the Cascade Range." The corridor, which passes through old-growth
forests, is a critical link because it separates the unique plant and
animal species that live in the forests.
The research team
used Geographical Information System (GIS) technology to evaluate habitat
connectivity and to analyze the distribution of roadkill of deer and elk.
The team used snow-tracking to document highway crossings and animal distribution
along the highway. They used off-road, automatic cameras to identify wildlife
found near the highway; and they monitored bridges and culverts to find
out which species use these structures to cross the highway.
Both the research
results and methodology are valuable to transportation planners. For more information, contact Peter Singleton at (509) 662-4315 extension 226 or phsingle/r6pnw_wenatchee@fs.fed.us. |
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