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].

Renee-fig1

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.”

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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

[1] http://www.nwf.org/what-we-do/protect-wildlife/wildlife-corridors.aspx

[2] http://www.environment.nsw.gov.au/resources/nature/landholderNotes15WildlifeCorridors.pdf

[3] http://arc-solutions.org/new-solutions/

[4] http://www.hcn.org/issues/291/15268

[5] http://www.biologicaldiversity.org/publications/papers/wild-corridors.pdf

[6] http://conservationcorridor.org/corridors-in-conservation/man-made-corridors/

[7] http://www.scientificamerican.com/article/roadkill-endangers-endangered-wildlife/

(Photos)

[8] http://www.powerhousegrowers.com/wildlife-corridors-highways-built-for-paws-hooves/#prettyPhoto

[9] http://www.atlasobscura.com/places/natuurbrug-zanderij-crailoo

[10] http://www.theworldgeography.com/2012/06/unusual-bridges-for-animals-wildlife.html

[11] http://highwaywilding.org/

[12] http://trib.com/news/state-and-regional/article_d54eedeb-f85b-5f8a-9763-5a500d54dee8.html

[13] http://www.amusingplanet.com/2011/01/africas-first-elephant-underpass.html

17 thoughts on “Wildlife Corridors: A Solution to Ending Roadkill?

  1. leorah

    I had no idea there was any sort of corridor method in place for turtles. You mention that the current options are not super feasible or efficient – did you come across any proposed solutions to those issues?
    I also agree with your statement about having to design crossings with a target species in mind, but are there designs for complex corridors that could be multi-species friendly? I’m thinking of maybe examples where there are open and covered components to make bridges appealing for multiple kinds of animals. Have you seen anything like that, or would it be to economically unfeasible in your opinion?

    1. reneev Post author

      Leorah,

      The most effective solutions I found all involved using a target species. The paper by Monica Bond (source #5) has a lot of information on how to make the most effective corridors possible for several different species of animals.
      I’m sure a complex corridor for multiple species could be created in the U.S.! The largest wildlife corridor in the Netherlands (the top middle photo) is not only long enough to span 3 highways, it is also wide enough to allow prey species to feel safe. If we could build more extravagant corridors like this in problem areas in the U.S., that would be ideal.

  2. mplatt

    I agree with your comments on cost because unfortunately when it comes to conservation cost is one of the biggest factors in carrying out projects. I loved the idea of using old tunnels and bridges that are already in place but making them animal friendly! I think this is a brilliant idea that cuts costs and recycles old structures. While I believe in the intrinsic value of nature it might be hard to convince the people who might be paying for these projects with their tax dollars that it is worth it to save some of these species. I wonder how Canada and other countries who carry out these projects rationalize to the people that it is worth it to save species, like deer, which seem abundant in the wild. Opinions?

    1. reneev Post author

      From what I’ve read, Canada installed a lot of these wildlife corridors in Banff National Park. They do have some government funding for that reason, but they also generated public support by pointing out that it can total your car if you hit a deer or a moose on the highway. I think bringing the peoples’ safety into the issue makes it seem more acceptable to spend money on saving individuals of a non-threatened species.

  3. smorton

    I did not think about implementing water features into over/under passes, now that it has been brought to my attention it seems to make a lot of sense. Animals could be attracted to crossings with water and may encourage more crossings. However, for many prey species water can also be a source of danger/risk. By incorporating water you could draw animals to these structures but also cause them to use the space efficiently and move on to avoid that perceived risk.

    You make a good point in the forethought that is needed before construction. Understanding how these structures will be affected during seasonal changes or severe weather is important especially as the frequency of use increases. As animals rely more and more on natural byways the need for them to stay operational through all sorts of conditions will become increasingly critical.

    1. reneev Post author

      As you mentioned, maintenance of these corridors is especially important. Earthquakes, floods, and other natural forces could damage the corridors over time. I think it is not only important to create the structures with this in mind, but also to find a way to repair the structures without scaring the animals away at the sight of humans with big machines.

  4. Lisa Angeloni

    I agree that corridors are an important conservation strategy. They’re not only important in the form of underpasses and overpasses to prevent road kill (as you’ve described nicely here), but also in the form of habitat corridors between core areas to maintain connectivity among populations. In case you’re interested, here’s a book on the importance of connectivity in conservation: “Crooks KR & Sanjayan M, eds. 2006. Connectivity Conservation. Cambridge University Press”. Of course, I’m not recommending this book simply because I’m married to the lead editor!

  5. mberne

    I think that over/ underpasses are a great way to connect habitats! Unfortunately it is not as affordable as it should be. I have never thought about using preexisting structures as over/underpasses. Thats a great idea! I always see bridges that aren’t being used and I imagine there may be a few tunnels/ channels that go below that may be useful to smaller species such as frogs and turtles.
    I think its a good point to make that overpasses can be both beneficial and potentially dangerous for a species to use. Deer may increase their use of the new path, but wolves and other predators may discover the high abundance of prey, and begin to increase hunting in these areas! it important to know the behavior of multiple species in order for it to be successful.

    1. reneev Post author

      It’s definitely important to plan ahead when building wildlife corridors! Luckily, there are a lot already in place which we can learn from. There is a lack of studies focusing on changes in animal behavior and predator/prey interactions around wildlife corridors, but this would be really interesting to study to see if it would affect how the animals use the corridors!

  6. kburrus

    It is very interesting to hear that only certain species will use the underpasses and that they are built with a species in mind. It would be hard to decide which species you would want to use the pass especially if you are building it for ungulates and they don’t use it. I also think there should be more push to build these over and underpasses and to find ways to fund these things since they are so useful. You would think that some funding could come from the state since a lot of the collisions can lead to death.

  7. amajor

    I definitely like the topic that you’ve brought up here. While I’ve always known about wildlife being killed by car collisions, but I never knew that there were so many animals dead from that. I definitely like how you brought the statistics on that, bringing up just how disastrous it is for the wildlife. I also loved how you brought up the different types of wildlife corridors and, even better, I very much loved that you’ve brought up that not all corridors work for all wildlife (from turtles to wolves) and for all roads. By doing that last part, you’ve shown that while it is not the golden bullet, it is a way on preventing collisions between cars and while. So, I would have to say that your article here is a grand one.

  8. Lacey Humphreys

    I really liked how you covered a wide range of species, both large and small that are affected by highway development. One question that I have is how are larger animals affected by the fences and the tunnels built for the turtles? Does this fragment their habitat further for larger species living in the same habitat or are the tunnels large enough to fit carnivores and ungulates if need be?

  9. Amy D'Arcey

    Turtle tunnel!!!
    What a great idea and even if it’s not a perfect solution it’s still better than just letting all the deer get squashed.
    I wonder what we can do to solve some of the problems that they are having with these over and underpasses. The problem of the carnivores learning to pick off easy prey is a tricky one and I’m not sure what we can do. Perhaps change the amount of cover at the entrances in a manner that will favor the ungulates. Another problem is getting the animals to use them, which I think we could help a lot with using good habitat cues and other methods to make the animals feel safe. The size seems to be a big factor for the animals.

  10. ssteele1

    This is a really cool concept! It’s disappointing that they can’t be more universal, so that a more broad variety of species can use them to travel. I think you’re right about understanding the species your designing this for though. As we’ve seen time and time again, money can be irresponsibly wasted by not putting enough time into researching the species. I think this has a great potential to be used at any major road/highway, but before the funding will be available I think a more universal method should be invented/implemented.

  11. Savimay

    With how much habitat fragmentation is caused by human’s labyrinth of roads, wildlife corridors may be the most important conservation tool in America. Habitat fragmentation blocks gene flow and isolates populations making them more susceptible to local extinction. Having these corridors to allow for movement would be vital for connectivity and sustainable populations. There are also the benefits to humans, like preventing wildlife collisions. It’s a win-win for everyone!

  12. cfalvo

    I think it was a very interesting point to emphasize about different species requiring different types of corridors. It is important to think about from a behavioral standpoint the various reasons species need to cross roadways and the conditions in which they will or will not cross. In the turtle example I like the simple idea of blocking them off with small fences, but as far as buckets go I think tunnels are definitely more appropriate. Firstly because the turtle makes the decision of where it goes and is not disoriented after human movement, and secondly because tunnels would take much less human attention than buckets that need to be emptied.

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