The Case for More Wildlife Crossings

As humans continue to encroach on critical wildlife habitat, wildlife infrastructure projects commonly referred to as wildlife crossings offer a man-made solution to a pressing problem. They help protect threatened species and bridge fragmented critical habitat areas, assisting in the important effort to restore and elevate ecosystem health.

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To fully understand the need for wildlife crossings, it is first necessary to define and emphasize the importance of ecological corridors. In simple terms, they refer to areas of land that species move through to travel to and from key habitat areas. These natural corridors – defined by specific features such as topography, elevation, and vegetation type – are learned passages that animals use to obtain basic necessary resources like food, water, and shelter. 

But like much of the natural world, ecological corridors are facing increasing anthropogenic pressures. Urban expansion – housing, highways, and other necessary infrastructure – has been steadily encroaching into critical habitat for wildlife, damaging or even destroying ecological corridors. 

Wildlife crossings offer a solution to the pressures that have impeded these important ecological corridors. Placed in strategic locations, they help bridge the gap for animals whose ecological corridor has been fragmented by urban infrastructure. They come in varying shapes and sizes, ranging from underpasses and culverts to major bridges designed with the needs of specific animal species in mind to help facilitate the safe crossing of busy and dangerous roadways. 

Case Study: Mountain Lions and California

Mountain lions – also known as cougars or pumas – require immense territories to survive. An adult male’s home range often exceeds 100 square miles (259 square kilometers), while females navigate areas between 20 and 60 square miles. Because they depend on such vast landscapes for food, water, and mates, they have been hit particularly hard by urban sprawl. Major highways have fragmented their habitat, severing the ecological corridors they need to survive. 

This fragmentation is often fatal. Between 2016 to 2023,  at least 613 mountain lions were struck and killed by vehicles in California alone. These collisions are not just a conservation tragedy; they are a public safety and economic burden. It is estimated that wildlife-vehicle collisions cost California roughly $200 million annually in property damage and medical expenses. 

A reduction in the number of mountain lions has lesser known, indirect impacts as well. Without mountain lions to regulate deer and other herbivore populations, overgrazing has reached a breaking point. This loss of vegetation leads to soil erosion, a decline in plant diversity, and a systemic collapse of the ecosystem’s health. 

The Wallis Annenberg Wildlife Crossing

Wildlife crossings offer a blueprint for coexistence in an increasingly fragmented world. Leading the way is the Wallis Annenberg Wildlife Crossing at Liberty Canyon in Southern California. Spanning ten lanes of the 101 Freeway, it is the world’s largest project of its kind, measuring 200 feet (61 meters) in length and 165 feet (50 meters) in width. As it nears completion in late 2026, the crossing stands as a monument to a decade-long effort to reconnect a landscape fractured by urban sprawl.

The necessity of this specific location was identified as far back as 1990 by the Santa Monica Mountains Conservancy. For decades, the project remained a dream, stalled by private land ownership. However, through the persistent efforts of the National Park Service and local conservationists, the land was gradually acquired. Construction finally broke ground in 2022. While the project has navigated significant logistical delays and a budget that has climbed to over $100 million, its ecological value is considered priceless.

Conservationists are hopeful that the high cost of this project will pay off significantly with a reduction in the number of mountain lions and other animals struck each year in this part of the state. Their optimism is fueled by research and the success of another passage – the Laurel Curve Wildlife Undercrossing on Highway 17. Linking Santa Cruz to Silicon Valley, Highway 17 was once a deadly barrier for a mountain lion population struggling for genetic diversity.

Since that undercrossing was completed in 2022, the results have been staggering: in its first year, the tunnel was used by animals 934 times. “It’s a great victory for mountain lions, fixing older infrastructure for the benefit of wildlife is just the smart thing to do,” California Fish and Wildlife Director Chuck Bonham said.