New Wildlife Corridors & Success Stories

Guest Post by: Lotl Love, Axolotl VTuber

In the United States, road mortalities are a danger to the survival of at least 21 threatened and endangered species. As urban development continues, it’s more important than ever to look for ways to prevent fragmentation of critical habitats. Failing to do so would be a tremendous blow to the native wildlife populations everywhere. Thankfully, many states are incorporating wildlife crossings and corridors. Bridges and tunnels that go over or under traffic have been popular in Europe since the 1950’s when the first one was built in France, however, they’re starting to become more common in the U.S. If you don’t know what you’re looking for, they tend to look like a typical overpass for cars. In reality, they are decked out with native flora and serve as a safe way for animals to cross from one side to the other. Although people tend to think of wildlife bridges over highways, there are also undercrossings which go underneath highways to offer a path for shyer and smaller animals.

Florida Builds a Wildlife Underpass

In the State of Florida, a wildlife underpass is currently being established on I-4 between Orlando and Tampa. The state has been working on a series of underpasses to allow animals to once again follow their natural migration pathways through a wildlife corridor that will reconnect two sections of a wildlife management area that had been disrupted by the highway since the 1970’s. The highway has been a huge barrier to wildlife movement since over 100,000 cars travel on that roadway every day and there is no way for wildlife to safely cross. And, when they do, they are likely to be hit by a vehicle which is dangerous to not only the animals but to drivers as well. As a result, it has blocked genetic exchanges between animals and restricted access to their natural range.

In addition to being terribly sad and dangerous, the crashes are very expensive as well. According to the Western Transportation Institute at Montana State University, after considering human injuries and death, towing, repairs, investigations by authorities and disposal of animal carcasses, costs can range from $8,190 for a deer-car collision, $25,319 for an elk-vehicle collision and $44,546 for a moose-vehicle collision. However, wildlife over and underpasses have become a very effective solution around the world to prevent these unsafe wildlife crossings, and benefit both the health and safety of people and the animal populations that depend on access to other parts of their natural range.

The new underpass in Florida is expected to be completed by the end of next year. Animals such as deer, bobcats, racoons, armadillos, coyotes, possums, black bears and panthers are expected to make use of the corridor. 10-foot high fencing that spans 1.5 miles will be used to steer animals away from the highway and towards the safe wildlife corridor. The state also has a variety of other wildlife corridors established throughout the state, in large part due to the Florida Wildlife Corridor Foundation, with the goal of creating enough green corridors to address habitat loss and fragmentation across the state and ensure the survival of native species. Alligator Alley, a major highway that crosses through the Florida Everglades, has 38 dedicated wildlife crossings and more are planned for other major highways throughout the state. 

Photo by Steve Newborn/ WUSF Public Media

California to Have the Largest Wildlife Crossing in the World

Florida isn’t the only one that is working to re-connect animal ranges. The largest wildlife crossing in the world is now being built in California, and it is set to change the lives of mountain lions and many other animals that live in the Santa Monica Mountains. While highways have benefitted efficiency and improved transportation, it has led to fragmented habitats and increases in road mortality for animals that are threatened and endangered. The Wallis Annenberg Wildlife Crossing will span across 10 lanes of Highway 101. Crews started to break ground on the $87 million wildlife crossing project in mid-April 2022 and the goal is for it to be completed by 2025.   

Render of the Annenberg Wildlife Crossing published by the Wallis Annenberg Foundation

Over the last 20 years, the National Park Service has been studying the animals in the Santa Monica Mountains and they’ve identified that urban development has genetically isolated mountain lions in the region, and without an influx of genetic diversity soon, they would become extinct within the next 50 years. 

In a UCLA-led study, scientists have identified the first reproductive signs of inbreeding among Southern California mountain lions (also known as cougars). They have been cut off from other cougar populations, and therefore other breeding options, by the busy freeways. Some of the mountain lions observed had malformed sperm, deformed tails, or testicular defects which are all signs of inbreeding. For an animal that is already locally endangered, it lends increased urgency to establish wildlife crossings and other structures so that they can roam further and find a larger pool of potential mates. These findings were also significant because mountain lions are considered an indicator species, which signals the health (or lack thereof) of environmental conditions. Knowing that cougars are isolated and have begun inbreeding, is a warning that we may start to observe other species resorting to inbreeding as well if something does not change. 

However, the new crossing offers huge relief for concerned environmentalists who have been working hard to bring this project to life. Upon completion, the crossing will span 165 feet to connect the Santa Monica Mountains with the Simi Hills, which are about 10 feet above the major freeway. To put it into perspective, an American football field is 160 feet wide. Like most crossings of this kind, it will be surrounded by trees, bushes, and sound barriers to make sure that the sounds of cars and traffic down below wouldn’t scare animals away from using it. By connecting the Santa Monica Mountains with the Simi Hills, mountain lions, as well as many other animals in the region, will be able to intermingle with other populations. At least 25 big cats have been killed while trying to cross freeways in Los Angeles since 2002. With the new crossing, there will be a significant reduction in the number of big cats killed on freeways. 

In 2012, the Wyoming Department of Transportation established six wildlife underpasses and two wildlife overpasses along a critical migration area for mule deer and pronghorn. The project was a huge success with vehicle-wildlife collisions reduced by 79% for mule deer and 100% for pronghorn.

Here are some other success stories that show how well wildlife corridors have worked throughout the U.S. 

Arizona – Bighorn Sheep

The Arizona Department of Transportation built three wildlife overpasses in 2011 over U.S. Highway 93 to help desert bighorn sheep safely cross the busy highway. There had been a steady increase in truck traffic and it is one of the main highways used by visitors to Las Vegas, Nevada. These overpasses have helped promote the survival of the largest population of desert bighorn sheep in the Western United States. As of 2020, the overpasses have been used by bighorn sheep, bobcat, gray and kit fox, deer and coyote more than 6,000 times!  

California – Yosemite Toad

Along stretches of the Sierra National Forest roads, the endangered Yosemite Toad was struggling to cross from its upland habitat on one side of the roadway to its wetland breeding habitat on the other side. Through a collaboration between the Forest and the U.S. Geological Survey, an elevated roadway on a 100-foot long portion of road was made along a section where they had discovered high toad mortality which was reducing the chances of the species’ recovery. Along with the raised roadway, fencing was added to funnel toads towards and under the elevated crossing which served as an underpass so that the toads could cross safely beneath traffic. This crossing is much less small and narrow than other amphibian and reptile crossings and allows light and rainfall to enter, which makes the toads more likely to successfully trek across the road.   

Nevada – Mojave Desert Tortoise

In Nevada, along U.S. Highway 93 and 95, culverts that were originally used for water runoff have been retrofitted to allow Mojave desert tortoises to safely move across the highway. These tortoises are a threatened species and had been further declining in numbers due to road mortality. Since tortoises were observed to use the culverts, the Nevada Department of Transportation worked to retrofit them to be better suitable as pathways. They also implemented fencing and “tortoise-walks” that navigated them around plunge pools that form on the downhill side of culverts. There are still many challenges and issues that need to be addressed for the desert tortoises to be able to consistently and safely cross. Out in the desert, common erosion prevention techniques can make it difficult or impossible for tortoises to cross. Still, without erosion prevention, large water events that are common in the desert can impact the culverts and make them totally inaccessible to the tortoises. For now, however, the current retrofitted culverts offer a degree of safe passage for the tortoises while the Nevada Department of Transportation works on developing a next-generation design for underpasses to create a better, more stable future for the Mojave desert tortoise.

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