Wildlife Crossings

Wildlife Crossings

Bridges and tunnels specifically designed for animals can reduce the environmental impact of highways.


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Biology, Ecology, Conservation

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Roadkill is a serious problem for drivers in the United States. In the U.S. alone, there are more than a million automobile accidents per year involving wildlife. They cost more than $8 billion in medical costs and vehicle repairs alone.

If you care about the well-being of wildlife, the problem is even worse. According to some estimates, automobile collisions kill more than a million animals every day. For many species, it is the leading cause of death. Even worse, major roads can split up animal populations and destroy their habitats. Animals lose access to large areas of their habitats, which makes it much harder for many animals to find food and a mate.

Animal Crossings Becoming More Common

Aspeople have become more aware of the danger to humans and animals, animal crossings are becoming more common. The crossings cancome in many forms. The type depends on the species that need to cross and the geographic features of the land. The most common forms are bridges and overpasses, tunnels, viaducts and culverts. A culvert is a structure that allows water to flow under a road, railroad or trail from one side to the other side. Planners are increasingly including them when they design highways and road improvements. The crossings greatly reduce the number of collisions, provide a safe corridor for animals and reconnect animal habitats.

Wildlife bridges are usually covered in native vegetation. In the United Kingdom, people often call them "green bridges." The idea is to make the crossing look like a natural part of the landscape, so animals will cross there. The crossings often work best when fencing is placed on the side of the road to funnel wildlife toward the crossing.

The concept was first developed in France in the 1950s. It took off in the Netherlands, where more than 600 crossings have been constructed. They protect badgers, elk and other mammals. The Dutch built the world's longest animal crossing, the Natuurbrug Zanderij Crailoo, which spans more than 0.8 kilometers (0.5 miles). Wildlife crossings can also be found in Australia, Canada and other parts of the world. In the United States, the idea took a little longer to catch on. Wildlife bridges and tunnels began appearing here about 20 years ago.

Amphibian-Sized Village

One of the earliest U.S. crossings was in Davis, California. In 1995, the city built a 15-centimeter (six-inch) wide tunnel, or "ecoduct," to allow frogs to pass under a road to a wetland on the other side. The town's postmaster decorated an area to make it look like an amphibian-sized village, and named it Toad Hollow. Despite this, the frogs did not use it.

The corridors in Banff National Park in Alberta, Canada, are far more successful. Between 1996 and 2016, six bridges and 38 underpasses were built for wildlife to cross the Trans-Canada Highway, which bisects the park. Park officials counted more than 150,000 crossings by mammals such as elk, moose, black bears, cougars and grizzly bears. Studies show that the corridors have specifically helped the grizzly bears find a mate. In addition, the park saw an 80 percent reduction in motor accidents involving wildlife. These statistics show the benefits that can come from a real effort to integrate conservation and highway construction.

Tunnels Adapted for Animals

In parts of Queensland, Australia, the koala (Phascolarctos cinereus) population has declined at an alarming speed over the past few decades. Auto accidents were among the leading causes of koala deaths between 1997 and 2011, according to a government report. Between 2010 and 2013, the Queensland government built about a half dozen wildlife crossings. Several existing drainage tunnels under roadways were adapted for animals. The government added ledges, which were wide enough for small animals to cross without getting wet. One ecologist was surprised at how quickly the koalas adapted and began using the tunnels.

90 Percent Drop in Wildlife-Related Highway Accidents

In recent years, animal crossings have been built in the western United States. Since 2000, Arizona has constructed at least 20 corridors, each with funnel fencing. In a part of central Arizona where elk (Cervus canadensis) migrate, there was a 90 percent drop in wildlife-related highway accidents. In 2018, Washington state authorities were working on a wildlife bridge that spanned Interstate 90. The project consisted of multiple underpasses and at least two bridges to let wildlife pass between the northern and southern Cascade Mountain regions. Deer began using the bridge at one of the passes even before it was completed.

Some types of wildlife crossings, especially overpasses, can be expensive to build. But they are cost-effective over the long term. When state legislatures plan highways, ecologists and conservation experts advocate for wildlife crossings to be included.

Media Credits

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Tyson Brown, National Geographic Society
National Geographic Society
Production Managers
Gina Borgia, National Geographic Society
Jeanna Sullivan, National Geographic Society
Program Specialists
Sarah Appleton, National Geographic Society, National Geographic Society
Margot Willis, National Geographic Society
André Gabrielli, National Geographic Society
Last Updated

October 19, 2023

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