Wildlife Crossings Cross One Risk Off the List

As urbanization spreads and the human population of earth grows, roads and highway systems are expanding to keep up with urban sprawl. It is well known that habitat loss is one of the more detrimental anthropogenic impacts to wildlife. But what about roads specifically can be so harmful to animals? And is there anything we can do to mitigate these impacts?

First of all, the sheer stress that traffic noise elicits can have quite the negative impact. Birds are one unlucky recipient of the brunt of negative effects of roads. Obviously, most birds do not need to cross a busy street on foot and can instead just fly right over. However, birds often have to compete with the loud, low hum of traffic noise when emitting calls to find a mate or defend their territories. Traffic noise has even been shown to cause changes in breeding patterns, increase stress levels, and change how birds interact with their offspring (Halfwerk et al., 2011).

Furthermore, roadways by design fragment wildlife habitat and act as a literal barrier for animals that can prove fatal to attempt to cross on foot. Collisions with vehicles are all too common in cities, as I am sure we all are familiar with seeing an animal laying on the side of the road after an unfortunate encounter with a car or truck. Deer, opossums, squirrels, and even mountain lions (among many other animals) are all examples of creatures who too often meet unfortunate ends while trying to cross a street to find food, a mate, new territory or to escape predation.

So, what can be done to mitigate the impacts roadways have on wildlife? While the impacts from traffic noise are harder to alleviate, there is a solution to help with the fragmentation roads cause and danger associated with attempts to cross them. Enter: wildlife crossings!

Wildlife crossings are exactly what they sound like: a corridor designed to link habitats on either side of a roadway or other barrier, which will help restore landscape connectivity and give wildlife a safe way to cross the street. The first wildlife crossing was built over 60 years ago in Florida. Now, wildlife crossings are often incorporated into early highway planning stages and may even be added as retrofits to existing highways (Clevenger, 2005).

“Wildlife crossing 3” by afagen is marked with CC BY-NC-SA 2.0. To view the terms, visit https://creativecommons.org/licenses/by-nc-sa/2.0/?ref=openverse

Construction has recently started on what will be the world’s largest wildlife crossing, which will span 10 lanes of Highway 101 traffic in Los Angeles. The $87 million project is expected to be completed in 2025 and was primarily designed to give mountain lions a safe way to pass from the Santa Monica mountains, over the freeway, and into the Simi Hills of the Santa Susana mountain range. The population of mountain lions in this area also is suffering from inbreeding and a resulting lack of genetic diversity due to being surrounded by roadways and isolated to their “urban island”, which further underscores the importance of this project (Mossburg, 2022).

California Governor Gavin Newsom has pledged to contribute $50 million to other similar projects around the state (Mossburg, 2022). This project will also likely kick forward other wildlife crossing projects across the country (and perhaps the world). It is time to start incorporating wildlife considerations into our roadway plans to allow for safe passages. Next up, how to deal with all that traffic noise…



Clevenger AP. (2005) Conservation Value of Wildlife Crossings: Measures of Performance and Research Directions. GAIA 14(2):124-129.

Halfwerk W, Holleman LJ, Lessells CM and Slabbekoorn H. (2011) Negative impact of traffic noise on avian reproductive success. Journal of Applied Ecology 48:210-219.

Mossburg C. (2022, April 25). Construction starts on world’s largest wildlife crossing to let animals roam over 10 lanes of L.A. highway. CNN. Retrieved from https://www.cnn.com/2022/04/23/us/california-wildlife-crossing-scn-trnd/index.html.

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