WSDOT builds wildlife crossings on I-90 near Snoqualmie Pass

When animals become isolated, they can lose genetic diversity, making them less resistant to disease and changes in their environment.

EASTON, Wash. — The Washington State Department of Transportation (WSDOT) broke ground on Phase 3 this year on a 15-mile stretch of Interstate 90 between Hyak and Easton which will include new wildlife crossings.

The crossings will help reconnect animals to habitats from which they have been cut off due to high volumes of interstate traffic, joining existing crossing structures that have already had an impact on wildlife.

According to Patty Garvey-Darda, a wildlife biologist with the US Forest Service, the ecosystem in the Cascade Mountains on either side of I-90 is changing rapidly and as a result is teeming with biodiversity. The project area is in the rain shadow of the crest of the waterfall. The top of the pass sees about 140 inches of precipitation annually, but just 15 miles to the east, that number drops to 60. Over that distance, “the set of species changes every step of the way,” Garvey said. -Darda. “Either vegetation or small mammal communities.”

In many places, I-90 prevents wildlife from moving between the north and south Cascades. Glen Kalisz, a WSDOT wildlife biologist, said studies have found that any highway carrying more than 10,000 vehicles per day is a complete barrier to animal movement. I-90 averages 30,000 vehicles per day, with double that number on peak travel days.

“It’s essentially a giant wall that nothing can cross,” Kalisz said. “A lot of times, when you get over the 10,000 vehicle per day threshold, the animals stop trying to cross the road altogether. They may realize it’s a losing battle.”

Wildlife needs to move from one place to another for a variety of reasons, including finding food, finding a mate, and raising young. When animals become isolated by a main road, they may lose access to other breeding populations, risking inbreeding. When animals lose genetic variability, that could affect their ability to resist things like disease and other environmental changes.

“They just lose resilience,” Garvey-Darda said.

Isolation is more of an issue with animals trapped on the south side of I-90, between the South Cascades and the Columbia River Gorge. Research by Western Washington University and the Washington State Department of Fish and Wildlife shows that ibex living in the South Cascades have become isolated. A master’s thesis by a Central Washington University student found the same thing about western toads.

Encouragingly, the existing wildlife crossing structures along I-90 have biologists optimistic about what kind of impact future structures could have, and not just on larger charismatic species like bear, deer or elk. .

Using a variety of monitoring programs, WSDOT is documenting about 4,000 successful wildlife crossings a year, approaching 20,000 total successful crossings since Phase 2 projects were completed several years ago. While most crossings are by larger mammals, monitoring by Central Washington University has shown species like coastal giant salamanders using structures to safely cross under the road.

“Two years in a row they have documented western toads breeding at the southern end of the overpass and have even documented small toads, little things about the size of a dime crossing the overpass,” Kalisz said. “So everything from toads to moose have been very consistently documented.”

This August, a moose was seen using an underground crossing at Resort Creek, which is just southwest of Snoqualmie Pass. Another moose sighting was reported in the same area in September, and eventually a sighting was reported in Mount Rainier National Park, which is the farthest southwestern location a moose has been seen in Washington state.

“That moose was huge, really huge from the standpoint of what we wanted to achieve,” Garvey-Darda said.

The variety of species that take advantage of the crosses and the consistency with which they are used represent great success in what biologists call “habitat connectivity,” a term that describes how the landscape “facilitates or impedes the movement of animals and other ecological processes,” according to the National Wildlife Federation.

While many other states across the country are focusing on how larger animals move from one place to another, WSDOT’s program is ahead of the rest in considering how large mammals, small mammals, amphibians, reptiles, mollusks, mushrooms, and even a lone moose can outrun the interstate. to reconnect the ecosystems of Cascade.

“I-90, Snoqualmie Pass East Wildlife Crossing Structure project is unique, and arguably internationally renowned for the fact that it strives to provide complete ecological connectivity,” Kalisz said. “WSDOT as a whole really emphasizes total ecological connectivity. We care about porcupines just like we care about deer, cougars, and bobcats, and we want to provide connectivity for them.”

“That’s what people don’t realize, is that they think of these charismatic animals like bears and cougars and moose and deer and now moose, but they don’t think of all the other species out there. We have at least 52 species of mammals that we are trying to connect, and then there are a lot of amphibians, reptiles,” said Garvey Darda. “So basically there are over 100 species that are just vertebrate species that we’re trying to connect. It’s not just a small number of species; its alot.”

In future phases of construction, there are plans to build another 15 medium and large wildlife crossing structures, including another flyover. The newer structures will open up to more terrestrial habitat, which Kalisz hopes will translate to more crossings in the coming years, including carnivores, as the animals become more comfortable with the structures and return in the future.

When the next wildlife crossing structures are completed, around 2030, the entire project will have spanned three decades.

“I hope future wildlife crossing projects on other highways don’t take as long,” Kalisz said.

Fortunately, federal funding for these types of projects is available for the first time with the passage of the infrastructure bill. In the past, Kalisz has said that WSDOT-led projects like wildlife crossing structures would lose funding compared to other road and maintenance-related work. While he hopes more funding will be needed, it’s a start.

“We have tons of research,” Kalisz said. “I like to say that we know what to do and we know where to do it. We just need to find the money to do the job.”

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