Wildlife habitat connectivity - Projects & progress

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Projects & progress

Performance analysis

2022

Projects including terrestrial habitat connectivity and fish passage protect wildlife resources

The concepts of fish passage and terrestrial wildlife habitat connectivity are linked. Riparian corridors (where aquatic and terrestrial environments meet) comprise small portions of the landscape but provide disproportionately important ecosystem functions. These areas are commonly used by wildlife to travel between patches of suitable habitat, and in highly fragmented urban landscapes, represent some of the last remaining travel routes available.

Completing terrestrial wildlife habitat connectivity and fish barrier removal work leads to engineering efficiencies and cost-savings. Combining these types of projects typically results in only minor cost increases over the fish passage-only plans, while constructing standalone wildlife crossing structures would be significantly more expensive. However, not all fish barrier removal projects offer the same potential benefits to terrestrial wildlife. Therefore, locations deemed important for terrestrial wildlife connectivity are prioritized using WSDOT's Habitat Connectivity Investment Priorities. If a project falls in or adjacent to a one-mile segment ranked high for either Ecological Stewardship or Wildlife-related Safety, it receives recommendations on how to enhance it for terrestrial wildlife passage.

The recently completed Indian Creek fish barrier removal project on US Highway 101 resulted in a wildlife underpass large enough to safely pass all species of animals on the Olympic Peninsula, including elk. Within weeks, a mink was recorded using the underpass and the first month of camera monitoring revealed several black-tailed deer herds crossing as well. Two years of pre-construction monitoring documented no native species crossing beneath US 101 using the old structure.
Indian Creek culvert before barrier removal
Indian Creek culvert before barrier removal.
Indian Creek crossing after barrier removal
Indian Creek crossing after barrier removal.

WSDOT developing statewide Habitat Connectivity Priority Zones

WSDOT is developing statewide Habitat Connectivity Priority Zones to help direct limited resources, including grant funding, to highway segments most needing wildlife crossing structures to increase habitat connectivity or reduce wildlife-vehicle collisions. The zones will be used to communicate priorities and coordinate solutions with partners.

Like the Habitat Connectivity Investment Priorities, the Habitat Connectivity Priority Zones are built around WSDOT's two-pronged approach to wildlife connectivity planning, utilizing Ecological Stewardship and Wildlife-related Safety categories. However, the HCPZ are characterized by longer, contiguous road segments ranging from approximately four to 30 miles in length. The HCPZ are distinct from the HCIP that rank the highway system at one-mile intervals which are primarily used for internal planning at WSDOT.

The top 15 Habitat Connectivity Priority Zones are expected to be published mid-July 2023, after an in-depth review conducted by government biologists, tribes, and environmental non-profit organizations.

Even though the HCPZ are currently in draft status, there are two locations that are indisputably Habitat Connectivity Priority Zones: US Highway 97 between Riverside and Tonasket, and Interstate 5 in the Castle Rock vicinity.

US Highway 97, roughly between the towns of Riverside and Tonasket, is the worst deer-vehicle collision area in the state. This approximately 14-mile stretch of highway is the scene of over 100 recorded deer-vehicle collisions yearly, resulting in significant property damage, wildlife mortality, and about two human injuries annually. Research suggests around three times as many large animals are killed on highways than reported in carcass removal data, so it's estimated that at least 300 mule deer are killed along this short stretch of highway every year. This extremely high level of collisions is partially because this road passes through the migratory path of Washington's largest mule deer herd and the traffic volume (around 4,600 vehicles per day) is low enough to encourage crossings but high enough to frequently result in collisions.

In addition to large mule deer herds, this stretch of highway is adjacent to habitat that supports many low-density, rare, or at-risk species, such as all three of Washington's native cats (Canada lynx, cougar and bobcat), as well as endangered grouse. Furthermore, species long absent from the landscape, such as pronghorn and threatened Canada lynx, are being reintroduced and will live in close proximity to this highway, bringing new species into consideration.

A Canada lynx strolls by a wildlife camera near the US 97—Riverside to Tonasket Habitat Connectivity Priority Zone
A Canada lynx strolls by a wildlife camera near the US 97 Riverside to Tonasket Habitat Connectivity Priority Zone.

Few safe crossing opportunities exist for wildlife here, and 468 large animals were hit and killed in this corridor between 2018-2022, most of them mule deer. With the average cost of a deer-vehicle collision estimated around $9,867, the 468 large animal collisions recorded in this 14-mile corridor represent over $4.62 million of economic impact.

In 2019, Conservation Northwest and WSDOT installed one mile of wildlife barrier fencing attached to a pre-existing crossing structure over the Okanogan River, Janis Bridge (at the northern end of the US 97 Riverside to Tonasket HCPZ). This wildlife barrier fencing helps prevent animals from crossing at unsafe locations and guides them to the crossing at Janis Bridge. In the three years since fencing was installed, WSDOT recorded an average of 2,500 safe mule deer crossings per year under Janis Bridge, representing 2,500 times a year that large mammals did not try to cross through traffic. Nineteen other species were recorded using the Janis Bridge crossing since the fence was completed. Furthermore, average annual deer-vehicle collisions near Janis Bridge decreased by 80-90% in the three years since the one mile of wildlife barrier fence was completed.

A herd of mule deer move single file through the Janis Bridge wildlife underpass
A herd of mule deer move single file through the Janis Bridge wildlife underpass. These animals represent six of the nearly 2,500 safe mule deer crossings documented per year, three years in a row.

While successes have been recorded for the Janis Bridge project, Phase 1 only addressed one mile of the 14-mile Priority Zone. There is local, state, and tribal support for building wildlife crossings in this area due to the potential significant increases to motorist safety and benefits to wildlife populations. WSDOT and Conservation Northwest are working to secure funding for Phase 2 of this project, which will include two new wildlife crossing structures, fencing linking them together, and additional features to support connectivity and reduce collisions. Funding for Phase 2 will be supported by $2.7 million allocated by the Washington State Legislature.

Interstate 5 in the Castle Rock vicinity bisects a critical wildlife corridor linking the Cascade Mountains to the Willapa Hills, and by extension, the Olympic Peninsula. This approximately nine-mile stretch of interstate is one of only two locations identified along I-5 that could provide connections between these diverse ecosystems, and opportunities to bridge this barrier are dwindling due to rapid development of adjacent areas.

The I-5 Cowlitz to Toutle Rivers Priority Zone sees an average of 40,000 vehicles per day across six lanes of traffic, while 10,000 vehicles per day or greater is generally considered a total barrier to wildlife movements. Recent research indicates cougars west of the Interstate are genetically isolated from populations east of it, and I-5 and associated traffic were identified as the barriers limiting animal movement between habitats on either side. This area has not only been identified as a cougar corridor, but also a corridor for elk, black-tailed deer, and other species. However, safe crossing opportunities are currently limited in this zone.

The I-5 Cowlitz to Toutle Rivers Habitat Connectivity Priority Zone, facing north
The I-5 Cowlitz to Toutle Rivers Habitat Connectivity Priority Zone, facing north. This highway has an average of 40,000 vehicles per day across six lanes of traffic, while 10,000 vehicles per day is considered a complete barrier to wildlife movements.
A collage of cougar detections along the interstate in the I-5&mdashCowlitz to Toutle Rivers Priority Zone
A collage of cougar detections along the interstate in the I-5&mdashCowlitz to Toutle Rivers Priority Zone. Vehicle headlights from I-5 are visible behind the cougar in the top right panel.

2021

Butler Creek project combines terrestrial and aquatic connectivity efforts

The Butler Creek Undercrossing project on US 97 was completed in 2012 and improved habitat connectivity for aquatic and terrestrial wildlife alike. The project replaced a 10-foot diameter culvert, which was a fish passage barrier, with a 65-foot span bridge that allows passage for all animals. This section of two-lane highway historically experienced high deer-vehicle collision rates, which provided an opportunity to improve aquatic and terrestrial habitat connectivity while also reducing the potential for dangerous wildlifevehicle collisions.

To create a successful safe crossing for terrestrial wildlife, features were included such as wildlife barrier fencing and multiple wildlife jump-outs (safe exits for animals that find their way inside the fencing).

Since this project was completed, the annual number of wildlifevehicle collisions has decreased by 81% within a half mile of the fence ends in both directions. In addition, fish are able to access habitat upstream of the highway. There are roughly 500 recorded deer crossings per year at this location, and many other species also use the underpass, including black bear, bobcat, coyote, cougar, California ground squirrel, endangered western gray squirrel, wild turkey, raccoon, and great blue heron.

wildlife crossing structure on US 97 at Butler Creek
A raccoon family uses the combined fish and terrestrial wildlife crossing structure on US 97 at Butler Creek. WSDOT's restoration team tended the vegetation so well that small animals can sometimes be difficult to spot.

Janis Bridge project reduces deer-vehicle collision rate by 91% in the area

On US 97 near the Canadian border, the 12-mile stretch between Riverside and Tonasket is one of the worst deer-vehicle collision areas in the state. In addition to large mule deer herds, this stretch of highway is adjacent to habitat that supports many low-density, rare, or at-risk species—such as all three of Washington's native cats (Canada lynx, cougar and bobcat)—as well as endangered grouse. Furthermore, species long absent from the landscape, such as pronghorn, are being reintroduced and will live in close proximity to this highway.

Few safe crossing opportunities currently exist for wildlife here, and 452 large animals were hit and killed on this corridor between 2017-2021, most of them mule deer. With the average cost of a deer-vehicle collision estimated around $9,175, the 452 large animal collisions recorded in this 12-mile corridor represent over $4.15 million of economic impact.

In 2019, Conservation Northwest and WSDOT installed one mile of wildlife barrier fencing attached to a pre-existing crossing structure over the Okanogan River, Janis Bridge (at the northern end of the US 97 problem area). This wildlife barrier fencing helps prevent animals from crossing at unsafe locations and guides them to the crossing at Janis Bridge.

In 2020, the first year after the wildlife barrier fence was installed, WSDOT recorded 2,194 mule deer crossings at the Janis Bridge structure. That number increased to 2,432 in 2021 (cameras were down for 40 days, so actual numbers were higher). In addition, 18 other species were recorded using the Janis Bridge crossing in the two years since the fence was completed.

Average annual deer-vehicle collisions in the vicinity of Janis Bridge decreased by 91% (11 per year in 2017 down to one deervehicle collision in 2021) since the completion of the one mile of wildlife barrier fence.

Providing safe passage for wildlife in this 12-mile corridor (between Riverside and Tonasket) is a top habitat connectivity priority in Washington. Realizing this, the legislature recently awarded $2.7 million to begin addressing these needs.

A herd of mule deer uses Janis Bridge to safely pass beneath US 97
A herd of mule deer uses Janis Bridge to safely pass beneath US 97. Retrofitted wildlife barrier fencing, which guides animals to the pre-existing structure and keeps them off the roadway, is visible in the background.

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