On The Move: Barriers To Wildlife Migration

Originally published March 14, 2021

Each year, millions of animals embark on seasonal migrations that move them from one region to another. This phenomenon is found in all groups of animals including mammals, birds, fish, reptiles, insects, and amphibians.

Here in Oregon, we host an array of moving wildlife populations throughout the year. One of the most ubiquitous migrators of the Pacific Northwest are our salmon and lamprey populations.

The fish are diadromous (there’s a vocab word for you!), meaning they move between freshwater and saltwater. In adolescence, these fish migrate from their riverside birthplace out to the open ocean, where they mature until they are ready to return to spawn and create the next generation. The routes between species’ summer and winter habitats are known as migration corridors.

These paths, travelled by generations of animals, are increasingly difficult to pass due to human infrastructure. Busy roadways, restricted access through walls and barriers, and even light pollution are making it more difficult and dangerous for animals.

In the 1980s, over 10 million Western monarchs arrived at their winter home in coastal California. In 2017, there were only 300,000. For mule deer in the Cascades, winter habitats are becoming more difficult to travel to, and increased traffic on Highway 97 presents an increasingly dangerous obstacle.

“Every animal has to move to fulfill its full suite of life needs, and when a road is smack in the middle of that particular need to cross, a problem is created,” says Simon Wray, a Conservation Biologist from Oregon Department of Fish and Wildlife. “Animals will follow vegetation cover, so they can get up to a highway while they’re hidden and hop across. [Or] it could be topography. Animals will follow ridgelines, stuff like that.”

In Oregon, over 7,000 collisions are reported annually. The death toll of animals is estimated to be 3-5 times higher than that, with up to 35,000 animals killed on roads in this state alone. Accidents account for up to 20% of mule deer deaths. Each year, an average of two people die from animal-related wrecks statewide. Wildlife collisions cause an estimated $44 million in vehicle damages yearly.

With statistics like these, it’s in everyone's best interest to protect and strengthen habitat connectivity for migrating wildlife. At the Oregon Wildlife Foundation we are partnering with the Oregon Department of Fish and Wildlife, Oregon Department of Transportation, Oregon Hunter’s Association, Oregon Watershed Enhancement Board, Mule Deer Foundation, and Protect Animal Migration to fund the Gilchrist Wildlife Undercrossing Project.

This undercrossing is being built in Gilchrist, Oregon as an added feature of a passing lane project by the Oregon Department of Transportation. As a busy Central Oregon intersection, Gilchrist has been identified as a hotspot for wildlife collisions; the project hopes to reduce the number of deer and elk being stuck by vehicles by providing an alternative to crossing busy Highway 97.

In areas where similar underpasses have already been implemented, the numbers are remarkable. The Lava Butte Wildlife Crossing was completed in 2012, and has reduced wildlife-vehicle collisions in the area by 85%. Beyond benefitting deer and elk, game cameras have captured over 41 different species using the undercrossing to make safe passage.

Mammals aren’t the only ones who benefit from connected movement corridors. For our smaller amphibian friends, such as the Northern Red-legged frog, projects like the Harborton Frog Shuttle make movement safe, and maybe even luxurious. In the northwest Portland town of Linnton, a group of dedicated volunteers physically assist the Red-legged frog population migrate twice per year.

These frogs travel to and from Forest Park and Portland General Electric’s Harborton Wetland property at the beginning and end of their breeding season. To make the journey from their elevated inland habitat to their breeding grounds in the wetlands below, the frogs need to travel about a mile across two local roads, busy Highway 30, and two sets of railroad tracks—often making the trip during rush hour in the early darkness of December and January.

Since 2013, volunteers have been taking shifts to monitor population movement. When the frogs begin coming out to move towards the Willamette River, they are scooped up and placed into buckets to be safely transported down the road. Prior to release, they are sexed and counted, and the process is repeated when it’s time for them to make the return journey later in the season. Like the highway underpasses, this project has proved successful.

In the 2013-2014 season, around 560 frogs were transported. In the 2018-2019 season, over 1200 frogs participated in this free taxi service, resulting in 165 egg masses reported by Portland General Electric. Fewer frogs are ending up squished on the road, and the Forest Park Red-legged frog population is thriving thanks to the work of dedicated citizen scientists.

With forward-thinking solutions and generous donations and funding, projects that support wildlife migration are being implemented statewide. These projects help everyone; “If you’re part of the traveling public, you don’t want to be running into deer,” says Tim Greseth, Executive Director here at the Oregon Wildlife Foundation. “If you’re a hunter, you’d rather see deer off the highway, somewhere else. And if you’re just an Oregonian who loves wildlife, you want to see [the animals] get to where they want to go, safely.”

Right now, the Gilchrist Wildlife Underpass is more than 85% of the way to reaching its fundraising goal. To donate or get involved, visit us at myowf.org. Additionally, you can remind drivers to watch for deer, frogs, and other Oregon critters by purchasing a Watch for Wildlife license plate voucher on our website. Proceeds from each plate sale will be directed back to the Foundation to fund habitat connectivity projects for migrating wildlife throughout the state of Oregon.