Improving wildlife habitat connectivity

Habitat connectivity is the degree to which the landscape allows animal movement and other ecological flows, such as water movement. Busy roads can create barriers to animal movements. Movement is the key to survival for many animals. They need to move from place to place for food, protective cover, and in response to seasonal conditions. Sometimes long distance movements are critical for finding mates or establishing a territory.

Most animals can cross a road with low traffic volumes without a problem. However, these roads tend to be in rural areas where more animals live. This means animals cross more often which results in more vehicle collisions than on roads with high traffic. For this reason, rural highways with moderate traffic volumes are the places best suited to measures reducing the risk of wildlife-vehicle collisions.

As traffic volume goes up, a vehicle is more likely to hit and kill an animal trying to cross. The less wary are killed and the more wary learn to avoid the road. Eventually, avoidance becomes the main response to a busy road and animals on either side of the road become isolated from one another. For this reason, the health and welfare of the animals deserves the most attention on high traffic roads.

See the examples below to learn more about what we do to improve wildlife habitat connectivity around the state.

We monitor some culverts and bridges to understand how animals use these structures. Wildlife structures, such as jumpouts and wildlife guards, are monitored to determine their effectiveness. View this video to see the variety of animals using these structures.

A cougar passes through a culvert designed for livestock.

We use fences to keep large animals off the highways. Studies show they reduce collisions between vehicles and large animals (mainly elk, deer, and moose) by 80 to 99 percent.

Gaps in fencing at intersecting side roads and on- and off-ramps are places where animals can gain access to the highway. To prevent deer and elk from entering the highway, we commonly use “wildlife guards” at these locations.

This 9 mile fence, completed in 2011, has reduced collisions between vehicles and deer and Bighorn Sheep on U.S. 97A north of Wenatchee.Wildlife guard in road intersecting U.S. 97 in Klickitat County.

Fences alone serve as barriers to important resources for the survival and successful procreation of animals. Combining fences with crossing structures either over or under the highway surface provide opportunities for animals to move past highways safely.

Artist's conception of a wildlife overpass under construction on I-90.

After replacing a bridge on U.S. 12 (at Casey Ponds), WSDOT designed an attractive path under it to provide safe passage for small animals under the busy highway. Grading and planting produced a more natural looking setting. The safe passage opportunity at Casey Ponds will improve as vegetative cover develops on the approaches to the bridge.

Bridge at Casey Ponds on U.S. 12 where WSDOT incorporated safe wildlife passage in bridge design.

We replaced the fish passage barrier on U.S. 97, north of Goldendale, with a structure large enough to accommodate both the stream and a variety of animals, including deer, which are generally shy of entering enclosed spaces. This project has significantly reduced the number of deer-vehicle collisions in one of the state’s worst problem spots. Correcting fish passage barriers, like the one featured in these before and after photos, is an opportunity to provide better conditions for terrestrial wildlife to pass safely under highways.

Before: This culvert was a barrier to fish and terrestrial wildlife.After: This bridge replaces the old culvert, providing passage for fish and other wildlife.

Median barriers are vital to motorist safety, effectively preventing head on collisions. On highways with lower traffic volumes, wildlife benefit from highway designs that allow easy crossings. We use median barriers designed with “scuppers,” a cutout in the base, to allow small animals to get past them easily (below left). The cable barrier is another good option to allow the safe crossing of animals. The ability to see easily past this type of barrier creates a willingness to go under or over the cables.

Cutouts in the base of median barriers intended to pass water also work well for small animals trying to get across a road.Cable barriers can function well for their intended purpose controlling errant vehicles while, at the same time, providing animals with easy passage across roads.

Future projects

This aerial photo shows a segment of U.S. 97, in Okanogan County, where two wildlife crossing structures have been proposed in an area with high deer-vehicle collisions and significant potential habitat linkage value for rare forest carnivores like Northern Lynx, Wolverine, and Grizzly Bear. Habitat connectivity between the Cascade and Rocky Mountains depends upon movement of animals through the Okanogan River Valley where U.S. 97 is located. Unfortunately, this project is currently not funded.

Future projects will consider not only correcting problems with wildlife-vehicle collisions but also the needs of wide-ranging species that must cross busy road corridors