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Wildlife Corridors: A Solution to Ending Roadkill?

One million! That is the number of animals killed by vehicles in the United States every day. “On U.S. highways, a vehicle hits an animal at least every 26 seconds” [1]. These animals range from small creatures like turtles and frogs, to larger mammals like deer and bears. This number even includes threatened and endangered species that are already struggling. With thousands of new drivers on the road each day, this is a problem that needs to be addressed before it gets any worse.

One way to effectively reduce roadkill is to build wildlife corridors. Wildlife corridors are “like roads for animals” [2], which help them travel across human roads safely. These animal passages, sometimes called Greenways, come in many shapes and sizes, and are common in some places around the world. Banff National Park in Canada is home to more than 25 wildlife overpasses across the TransCanada Highway [3]. In the Netherlands, over 600 underpasses and overpasses exist, making the country one of the leading experts in wildlife corridor construction [6].

Building wildlife corridors to help animals get past roads and other urban areas has been proven to reduce road kill rates. In Utah, a crosswalk system was created for local deer. After the first installations were completed, 40% more deer were able to cross the road safely than before [4]. In the Mojave Desert in Arizona, a conservation group was able to reduce turtle road kill by 93% after installing fences on either side of the highway and creating tunnels for the turtles to travel through [4].


Left: Wildlife bridge in Banff National Park, Canada. Middle: The longest wildlife bridge in the Netherlands, Zanderij Crailoo, which spans 800 meters long and 50 meters wide. Right: A wildlife bridge through the Veluwe natural area in the Netherlands [8,9,10].

Wildlife corridors range from simple bridges planted with grass to vast constructions including trees, shrubs, and sometimes even water. The most common type of wildlife corridor in the United States is the culvert, a large underpass tunnel. In order to understand why wildlife corridors are a sustainable and worthy use of our resources, we must understand something about an animal’s behavior. Why do animals cross roads, and how we can attract them to wildlife corridors instead?

Many species of turtles, for example, have specified breeding grounds which are often far from their usual habitat. In order to reach the area where they will mate, many turtles have to undergo seasonal road crossings. These turtles are not picky about where they cross the road, only that they arrive at the other side, so wildlife corridors for turtles can be relatively simple in design. On the east coast of the U.S., short fences are installed along the sides of many major highways to prevent turtles and other small animals from entering the roadway. In order to allow the animals to reach the other side, either deep buckets or tunnels have been created. In places where buckets are placed, people have been hired to collect turtles and frogs that fall into the buckets and relocate them to the opposite side of the road so that they may continue their journey. Tunnels are preferable because they do not require further human effort, but they are not feasible for roads with many lanes [5].

In contrast, wolves, such as the native populations of Yellowstone, cross roads for a different reason entirely. Packs of wolves have large territories and travel far every day to look for food and other resources. This puts them in danger every day of colliding with vehicles. An effective wildlife corridor for wolves would consist of more than a short fence next to a busy road. For larger mammalian species, bridges are preferred, but since they tend to be more expensive, large culverts are often built instead. These tunnels must be wide enough to ensure the animal feels comfortable, and not trapped. Drainage and flood water should also be kept in mind, so that the tunnels do not become inaccessible in certain weather or seasons [5].

Due to these behavioral differences between species, each corridor must be designed with a target species in mind. An underpass that works for a deer may not be effective for a frog or a bird. Therefore, it is important to understand the behavior of different animal species when considering a wildlife corridor. The behavior of the target species, including the animal’s reasons for crossing the road, must be taken into account when designing a wildlife corridor. Predation must also be kept in mind; an elk will not use an underpass tunnel if predators such as bears are often seen using the same tunnel. A corridor will only be effective if the animal feels safe using it. Therefore, different types of corridors are needed along the same stretch of road. According to Monica Bond, who has done extensive research on wildlife passages, wildlife corridors are most effective when they are placed directly adjacent to a natural area, and are planted with natural soil and foliage. To encourage animals to use underpasses and overpasses, human presence around the entrances and exits should be minimized and the edges of the overpasses should be covered in as much vegetation as possible, to prevent the animals from getting stressed at the sight of cars [5].

Many of the wildlife corridors that exist in Canada and the United States are repurposed bridges and underpasses that were no longer being used by humans. It is difficult and expensive to build new corridors around existing roads. If there are no existing bridges or underpasses available, the easiest way to implement wildlife corridors is to design them along with a new road, and then build both at the same time. This means that existing roads and highways are less likely to be fitted with corridors, because it is an expensive and time-consuming process [7].

In the larger scheme of things, wildlife corridors have been proven effective in reducing road kill rates all over the world. By studying the behavior of a target species and learning why they cross roads and how we can redirect them to a safer passage, we can make wildlife corridors increasingly effective. Supporting the creation of more wildlife corridors in the U.S. will convince municipalities to invest in building more, as well as set an example for other countries. Wildlife corridors are not a be-all and end-all solution to animal deaths, but they set the groundwork for saving species so that we can study them further and continue to learn from them.

As Beth O’Donnell Young, writer and landscape designer, said; “If you build it, they will come.”


Left: A grizzly bear in Banff National Park uses an underpass. Middle: Mule Deer in Wyoming are seen traveling through an underpass to cross a busy highway. Right: African Elephants in Kenya are seen emerging from a large underpass, measuring 15 feet high [11,12,13].

 –Renee van Ineveld

Class of 2015