“From the beginning, we knew our [bridge] had to serve a unique purpose in providing passage for people and wildlife.”
Denise Gross, Executive Director of the Phil Hardberger Park Conservancy
The U.S. has been a world leader in wildlife conservation laws, enacting some of the most effective measures to protect animals, such as the Endangered Species Act (ESA) of 1973, the Marine Mammal Protection Act (MMPA) of 1972, and most recently, the Preventing Animal Cruelty and Torture (PACT) Act of 2019.
Even so, U.S. wildlife populations are in decline. One in five animal and plant species in the country—nearly 1,300 total species—is at risk of extinction, according to the Center for American Progress. And the populations of more than two-thirds of all endangered species in the U.S. are falling.
The Living Planet report 2020 outlined the many reasons behind why we are still seeing numbers decline, but it all boils down to our increasing human footprint on wildlife areas, a significant part of which are our roadways. In the U.S., there are 21 species whose survival is threatened by road mortalities, including key deer in Florida, bighorn sheep in California, and red-bellied turtles in Alabama, according to National Geographic.
The total number of large mammal-vehicle collisions has been estimated at one to two million in the U.S., annually. And the rate of these deadly accidents is only growing.
“Over the most recently reported 15-year period, wildlife-vehicle collisions have increased by 50 percent,” Rob Ament, the road ecology program manager of the Western Transportation Institute at Montana State University told National Geographic.
These collisions are not only perilous for animals—they are also responsible for hundreds of human fatalities and over one billion U.S. dollars in property damage each year.
In December 2013, at its 68th session, the United Nations General Assembly decided to proclaim March 3 the international day of the adoption of the Convention on International Trade in Endangered Species of Wild Fauna and Flora, World Wildlife Day. In honor of the annual day of awareness, we are highlighting one of the major ways that wildlife is affected in the U.S.—roadways—and diving into how individuals can promote the wellness of their local wildlife.
How Roads, Highways, and Railways Impact Wildlife
According to the Department of Natural Resources Conservation of the University of Massachusetts, Amherst, the construction of roads affects wildlife in the following ways.
- Direct loss of habitat. Firstly, the construction of new roads and railways mean changes to the surrounding area, which greatly diminish wildlife habitat.
- Degradation of habitat quality. Stormwater discharges, alterations in stream hydrology, and air emissions that result from the construction of roads can negatively affect habitats up to several hundred yards from railways and highways.
- Habitat fragmentation. One of the bigger problems is the fact that roads, highways, and railways disrupt the continuity of animals’ habitat. The loss of interior habitat is problematic for edge-sensitive species and smaller overall patch sizes may result in the loss of area-sensitive wildlife.
- Road avoidance. Many wildlife species avoid areas near highways altogether, due to noise and human activity associated with roads, which has been documented for black bears, grizzly bears, wolves, bobcats, turkeys, caribou, and others.
- Increased human exploitation. Roads and highways also give hunters and poachers easier access to wildlife, decreasing animal populations in areas adjacent to roads and highways.
- Road mortality leading to loss of populations. Small roads are a significant source of mortality of wildlife, especially of reptiles and amphibians.
- Disruption of social structure. Roads and highways may have also decreased survival rates of certain mammals and disrupted social organization during mating season, due to the hesitancy of animals to cross the roads and find their mates.
- Reduced access to vital habitats. Railways and highways also reduce access to vital habitats for a variety of wildlife species that migrate over long distances seasonally.
- Disruption of processes that maintain regional populations. The continuity of habitat is also important for the maintenance of genetic viability within local populations of animals, and for maintaining local and regional populations in the face of population extinctions.
One Solution? Landbridges or Ecoducts
One of the solutions to this problem is wildlife bridges or ecoducts, which are constructions that allow animals to safely pass over or under highways. These bridges and tunnels have been popular in Europe since the 1950s when the first was built in France.
But experts say that the number of ecoducts is not nearly keeping up with the growing number of roads in the U.S. So, officials and biologists are looking for ways to expedite the construction of new bridges and tunnels, the REI Co-op Journal writes.
One of the most recent additions is the Robert L.B. Tobin Land Bridge at the 330-acre Phil Hardberger Park Conservancy in San Antonio, Texas, which opened in December of 2020.
Denise Gross, the executive director of the park, joined the park’s team seven years ago when it was still fairly new to San Antonio.
“I had been watching the development [of the park] and reading about it,” she said. “The concept of this preserved, natural area in the middle of the city was really exciting.”
When the land was purchased to create the park, there was a six-lane, 60 mile-an-hour highway that cut right through it, Wurzbach Parkway. The team’s challenge was to connect the two sides of the conservancy to create a safe passageway for the area’s surrounding wildlife.
“Even though you do put up barriers, [animals] get across or start to get across,” park namesake and former Mayor Phil Hardberger told KSAT. “Right now, it’s six lanes. [The Texas Department of Transportation] says it will eventually be eight lanes. We’ve had some accidents between cars and deer, especially, and some of the smaller animals as well.”
“From the beginning, we knew ours had to serve a unique purpose in providing passage for people and wildlife,” Gross said. “The team consulted with urban wildlife specialists to advise them on what is going to be needed so that wildlife really will use this. That helped determine the size of it and how it’s laid out.”
The bridge is 150 feet wide at the top, 165 wide at the base—broad enough for both animals and people to safely cross—and is one of the first bridges to serve both pedestrians and wildlife of its size in the U.S.
“It was a balance of those two things: What will work for people so we can connect the trails for them and what will work for wildlife so that they have safe passage from one side to the other?” Gross said. “And not just a safe way to get to the other side, but also to connect the wildlife. When you have islands that prevent wildlife from moving freely, you can end up with interbreeding, which weakens the species.”
Because highways act as barriers, they can isolate wildlife populations and alter gene flow and diversity, as previously mentioned. Wildlife crossings allow individual animals to mate with individuals in other populations, “thereby promoting genetic diversity needed for maintaining genetically viable populations.”
Early Success with the Hardberger Park Conservancy Ecoduct
Since the opening, there has already been a notable amount of wildlife using the bridge.
“Even while there was a lot of construction going on, they started seeing deer cross and coyotes. Those were the two earliest things,” Gross said. “And there was a lot of armadillo activity at one end of the bridge. Other species found in the park are squirrels, birdlife, possums, and bobcats. An urban biologist wildlife expert who visited recently said she thought it would probably be the smaller species that adapt first.”
A similar construction is underway 200 miles east, at the Memorial Park Conservancy in Houston. The ecoduct, which will cross over Memorial Drive, will reunite the north and south sides of the park to establish a crossing for both people and wildlife. The project also includes the addition of a stream corridor constructed through the prairie and a culvert under Memorial Drive.
“Together, these corridors will provide much-needed wildlife connectivity within Houston’s largest urban wilderness park and to the natural Buffalo Bayou corridor,” the team at Memorial Park told us.
The park is also tackling a prairie restoration, reintroducing endangered native Gulf Coast prairie, and additional wetlands to areas north and south of Memorial Drive.
“The land bridge and prairie will be composed of multiple ecologies that represent different types of habitat, including wetland, prairie, savanna, forest, and others,” the team said. “These habitats will nurture existing wildlife and attract additional species, thereby promoting biodiversity.”
The project is anticipated to attract 15 new bird species to Memorial Park—a 17 percent increase on a base of 88 species that have been identified in the Park. Construction began in August 2020 and is slated for completion in late 2022.
Because animals often exhibit a learning curve, it could take several years for all of the local fauna to find and habituate to these new structures, but both of these projects are sterling examples of investments in the future of wildlife in the U.S.
Supporting Wildlife in Your Own Community
Land bridges are one way that communities can promote the health of local wildlife, but what can individuals do to pitch in?
“I think creating habitat is probably the most important thing,” Gross said. “We think of those big species like mammals and reptiles, but even just creating habitat for pollinators and birds can be really important and is probably the easiest thing to do at home.”
The Phil Hardberger Park Conservancy has a wildscape demonstration garden that shows how you can select certain plants for your home garden that support wildlife. Creating an outdoor space that emulates the area’s natural environment allows natural systems to interact and establish an equilibrium.
Some features of your very own wildscape could include:
- Log piles, which are sanctuaries for insects, reptiles, and amphibians
- Bird feeding stations and birdhouses;
- Bug boxes and/or bee hotels; sources of water, such as a pond, for birds to drink and insects and amphibians to lay eggs
- Flowers rich in nectar to attract bees and butterflies
Your garden should include a range of plant types to act as different habitats. It is especially important to use species that are native to the area, as native plants will be more suited to local wildlife than non-native plants.
“Working and being supportive of projects like the landbridge is important. Ours had tremendous community input and support,” Gross said. “Part of the funding came through a city bond. It took getting the people to vote. Putting your vote behind these projects is another important thing.”