Wildlife Crossing on I-5 Near Castle Rock Could Be Key to Species' Survival, Advocates Say


Washington's growing urban landscape is causing a conundrum for wildlife roaming between the Cascade Range and Olympic Peninsula, and their main barrier is Interstate 5.

Researchers say wildlife crossings scattered along a 276-mile stretch of freeway will be vital in retaining natural habitats. Currents of swift traffic spanning multiple lanes on the freeway impede habitat connectivity, or the degree to which a landscape allows ecological flows.

Fortunately, I-5 is not impenetrable, and there may be a solution in Southwest Washington.

"Without thinking about connectivity, we run the risk of killing lots of animals via collisions ... but we also run the risk of cutting off natural wildlife movements and isolating wildlife populations," said Glen Kalisz, Washington Department of Transportation habitat connectivity biologist.

A "Cascade to Coast" analysis assembled by the Washington Wildlife Habitat Connectivity Working Group — an assortment of state agencies, nonprofits, universities and tribes — identifies key northern, central and southern linkage zones along I-5 that are undeveloped and host high concentrations of wildlife.

The southern linkage — tagged as the most robust of the three zones — is a forested area near the Toutle and Cowlitz rivers in Cowlitz County. It spans about 10 miles and would draw northern and southern swaths of land into a wide "U" shape.

Wildlife crossings are becoming standardized in road planning and may manifest as bridges and overpasses or tunnels and culverts. They can resemble something as substantial as Interstate 90's wildlife bridge east of Snoqualmie Pass or as small as Longview's squirrel bridges.

Overall, the infrastructure addresses the reality of altered ecosystems, biodiversity and ecological processes caused by highways.

Here, there aren't many opportunities for wildlife to cross. It's almost guaranteed the cougars, hoofed mammals and other creatures in that area would be killed if they attempted to traverse the freeway, Kalisz said.

Focal species addressed in the study include cougars, Western gray squirrels, Pacific fishers and mountain and American beavers.

Connectivity Means Longevity

Brian Stewart, Cascades to Olympics program manager with Conservation Northwest, said incorporating wildlife crossings is central to preserving a species' adaptation and evolution.

Maintaining habitat connections is essential to avoid extinction.

"If we want to have the flora or fauna around in the next 100 years, creating that landscape for them to adapt as they have for millennia is absolutely paramount," he continued, "or else exploitation and extinction will be the norm."

Bright flashes, loud engines and rumbling wheels deter wildlife from venturing near I-5. This might be ideal for reducing vehicular collisions, Stewart said, but avoidance has a resounding effect on animals' populations altogether, specifically due to a lack of genetic diversity.

Isolated gene pools are likelier to occur when animal populations remain in the same general location rather than reproduce with different groups farther away. These effects are already being seen in cougar populations exhibiting less genetic diversity on the Olympic Peninsula, spurring international organization Panthera to launch the Olympic Cougar Project.

Weakened genetics weaken animals' ability to adapt to changes in the environment and makes them more prone to illness. Evolutionary responses occur over long periods, though there could be observable variations within a species within decades, Stewart said.

Genetic diversity also builds resilience against environmental pressures caused by climate change — a phenomenon that pushes wildlife to seek refuge as their habitats are touched by rising water levels or altered by wildfires.

Now or never

Researchers say there's a sense of urgency in pursuing habitat connectivity along I-5 as 

Washington's Population Grows.

Cowlitz County, where the southern linkage is being proposed, is projected to build about 10,000 new homes within two decades to accommodate the state's housing needs, according to the Washington Department of Commerce. It's a fraction of the state's required 1.1 million homes, but every parcel of undeveloped land is critical for maintaining wild habitats, Kalisz said.

And that's just housing.

Conservation Northwest anticipates that warehouses, factories and various businesses will sprout along the state's main arterial as the state's population burgeons, prompting the organization and its partners to track development and land use changes.

"Once these areas are developed, they're practically gone from the wildlife corridor landscape forever," Kalisz said.

Fortunately, the southern linkage is "low-hanging fruit" in a sense. In that area, land surrounding I-5 is managed by the Department of Natural Resources and private timber company Weyerhauser, as opposed to its northern counterparts that are consumed by various private parcels.

None of it will be simple or streamlined, he said. Building wildlife crossings in priority linkage zones won't be helpful in the long term if the land is not protected.

"We're losing parcels every day," Kalisz said.

Washington is competing with other states to gather federal funding dedicated to habitat connectivity. In 2021, $350 million was committed to a wildlife crossing pilot program as a part of the Infrastructure Investment and Jobs Act. This funding was only allocated for five years, and the clock is ticking to apply — requiring project leads to assemble a feasibility study, which they have yet to complete.

Installing connections between the north and south Cascades across I-90 took about 30 years from conception to construction. Though it's one of Washington's greatest crossing achievements, it took a significant amount of time — something of which Cascades to Coast project leads are certain there is a limited supply.

Researchers are currently conducting preliminary biological studies and are aiming to draft a feasibility analysis within two years, which would examine engineering capabilities and cost estimates. Concurrently, the Washington Department of Fish and Wildlife is examining how to educate county planners on habitat connectivity for future land use projects.

"That almost seems too late," Kalisz said. "But you know, we don't really have a choice."

How to Help

There are volunteer options through Conservation Northwest, which consist of attending meetings and events, editing and doing restoration work. To review these opportunities and sign up for updates, visit www.conservationnw.org/take-action/volunteer.