Project Promises Safe Passage for People and Wildlife (November 2010)

Idaho Fish and Game News – November 2010

A cheer went up from Ed Bottum as he stood under the new wildlife underpass on State Highway 21.

“It’s a picture postcard of a wildlife underpass,” said Bottum, habitat biologist for Idaho Fish and Game. “It’s open. It’s tall. It’s wide. It should feel pretty comfortable to a deer or an elk.”

Ed Bottum

Ed Bottum

This winter, deer and elk migrating to the Boise Foothills and Boise River valley have another way to cross Highway 21 – under it.

Highway 21 connects Boise with the high country of the Boise National Forest. It also cuts through the migration route of one of Idaho’s largest deer herds. Every winter up to 8,000 deer and 1,000 elk drift down from the mountains in search of shelter and food to help them survive the winter cold.

Bottum manages the Boise River Wildlife Management Area, which is part of 36,000 acres of mule deer and elk winter range in the Boise Foothills and the Boise River Valley.

In the spring, mule deer and elk follow the retreating snowline back to their summer range.

With each migration, deer and elk cross Highway 21 at least once. The 11 miles closest to Boise are the most dangerous for motorists and wildlife.

“We’ve been tracking the number of deer and elk killed along this stretch of highway for the past 33 years,” Bottum said. “Since 2000, we’ve been losing around 100 big game animals a year, although in 2002 more than 230 were hit and killed by vehicles.”

The loss of life is hidden from most motorists because Idaho Fish and Game regularly picks-up carcasses from the road side.

“It’s a horrifying job to do,” Bottum said. “I’m not the only who’s done it, and I think it affects all of us the same way.”

To draw attention to the problem, two large highway signs were installed in 2009. They regularly update drivers on the number of deer and elk killed on this 11-mile stretch of highway each year.

Signs alert motorists of the danger of deer and elk on the road, but the long-term solution to the chronic problem of vehicle-wildlife collisions is to physically separate the two. After more than 30 years of counting dead animals, the state has taken this step at one location.

With the help of federal stimulus dollars, The Idaho Department of Transportation was able to design and fund an underpass and part of the wildlife exclusion fence. Three months of road construction and $750,000 later, the wildlife underpass and some of the exclusion fence is done.

“You ask an engineer to solve a problem for you and they will,” Bottum said. “Seeing this project go from an idea to cement and steel is an affirmation of ITD’s engineers ability and skills.”

Located at milepost 18.2, the 15-foot high and 30-foot wide opening lines up with two drainages heavily used by migrating deer and elk.

“What we have here is a natural funnel,” said Scott Bodie, with the Boise National Forest. “The deer and elk are moving up on the ridgeline, and they drop down the draws bringing them right through here.”

Biologists expect deer and elk that already migrate along this route to discover the underpass on their own and use it. But this represents a fraction of the animals that could be directed to the underpass.

ITD’s design calls for 1.65 miles of fence on the east side of the highway and one mile on the west side. Only part of the fence could be built with the funding available.

As the fall migration approaches most of the east side fence is not built, limiting the effectiveness of the underpass.

“Conditions haven’t really changed that much on Highway 21 for this winter,” Bottum said. “We won’t be able to say ‘look how well this works’ quite yet. But I’m optimistic more money will be allocated to complete this project.”

An estimated $450,000 is needed to complete the fence. ITD will continue to look for additional funding. The Boise River Wildlife Linkage Partnership, a collection of residents and agencies focused on reducing vehicle-wildlife collisions on Highway 21, has already raised $25,000 for the fence.

“Ultimately when the fence is complete,” said Marshall Haynes, senior conservation officer for Idaho Fish and Game, “there will be hundreds, if not thousands of animals that will be channeled through the underpass or around and down into the reservoir, animals that won’t have to cross the highway.”

When the underpass project is completely done both motorists and wildlife will have reason to celebrate.

For more information on wildlife crossings, Highway 21 and the Boise River Wildlife Linkage Partnership, visit