Crossing

Safe Detour for Bighorn Sheep

Authors and Contributors
Ron Wilson
Ram lying dead on side of the road
A number of bighorn sheep have been killed by vehicles over the years on U.S. Highway 85 in western North Dakota.

Life is difficult for bighorn sheep in western North Dakota, a population of about 350 animals that live in the most rugged and head-turning terrain the state has to offer.

Brett Wiedmann, North Dakota Game and Fish Department big game biologist, said biologists have been radio-tracking bighorn sheep for about 20 years and what they’ve found is that these animals die from a number of causes, including predators, traps, snares, barbwire fences, disease and getting hit on roadways.

“It’s 365 out here for these animals,” Wiedmann said. “Nature can be pretty tough on them, so anything we can do to minimize that mortality, we’ll do it.”

A project to alleviate vehicle-animal mortality in an area that harbors some of the best bighorn sheep habitat is underway near the Long X Bridge, just south of the entrance to the North Unit of Theodore Roosevelt National Park. It’s there, where a number of bighorns have been killed on U.S. Highway 85 over time, that a large and impressive wildlife crossing is being constructed to safely funnel bighorns, and other wild ungulates, from one side of the highway to the other.

The wildlife crossing, and construction of a new Long X Bridge, is part of a long-term effort of the North Dakota Department of Transportation to widen U.S. Highway 85 from two to four lanes from Watford City to Belfield.

“When you compare bighorn sheep to mule deer and white-tailed deer, they are just a tiny fraction of our other ungulates,” Wiedmann said. “So, every time you lose a bighorn, especially a bighorn ewe, that’s a big hit to the population. A pregnant ewe killed on the highway means you’ve potentially lost two animals, which is significant.”

Greg Schonert, North Dakota DOT biologist, said widening the highway through high-quality wildlife habitat means that animals, bighorns and others, will have to spend more time on the roadway when crossing, which could be a safety issue for animals and motorists.

“Historically, with all the oilfield traffic and agriculture traffic, there have been a lot of animal-vehicle collisions,” Schonert said. “One way to reduce that is to install a wildlife crossing to funnel them through and help maintain that habitat connectivity and reduce the number of collisions to make it safer.”

In 2019, Wiedmann said Game and Fish deployed GPS collars on some bighorn sheep in the area and learned that the animals crossed U.S. Highway 85 more than originally thought.

“We thought it was pretty rare for the ewes to be crossing, but as soon as we deployed GPS collars that collect daily locations, we learned that they were crossing quite a bit,” he said. “They’ve even been crossing during the construction project itself. So, this wildlife crossing, I think, is going to do wonders to reduce mortality.”

Wiedmann said there are a number of reasons why bighorns gravitate toward the highway. In fall during the rut, for instance, with ewes navigating the rugged terrain on both sides of U.S. 85, mature rams will cross often to check on adult females. And in spring, ewes will ease out of the hills to pick at the alfalfa adjacent to the highway.

“They’ve habituated to the road traffic, so they don’t really fear vehicles,” he said.

Bighorn mortality on U.S. Highway 85 got to be such an issue years ago north of Long X Bridge that the Game and Fish Department had to step in.

“There were bighorns north and south of Long X and the mortality got so intense on the north side that we actually had to go in and trap all those animals and move them out of there because they were getting killed at such a high rate,” Wiedmann said.

Because the road-widening effort from Watford City to Belfield is such a big project, especially when the safety of motorists and the safeguarding of the state’s natural resources must be taken into consideration, there were several obstacles to overcome.

GNF and DOT workers at construction site
Several players, the Game and Fish Department and the North Dakota Department of Transportation, to name two, work in coordination to complete the wildlife crossing near the Long X Bridge.

“It’s all been a big hurdle, quite honestly,” said Bruce Kreft, Game and Fish Department conservation biologist. “This project is running right through some of the most sensitive, critical habitat areas in the state. On top of that, you’ve got multiple groups – federal landowners, private landowners, different state and federal agencies – that had to come together to try and identify solutions to some of the impacts that were foreseen.”

Roger Hille, an engineer with AECOM, the consultant construction engineering company hired by North Dakota DOT for the project, said the wildlife crossing, which to the pedestrian looks like a giant culvert, is one of a kind in North Dakota.

“The first phase you can see is complete and that’s about 65 percent of the structure … the second part will be starting right after the Fourth of July,” Hille said. “When it’s all done and the animals are coming downhill, it’s going to look even more enticing for them, and I think they’ll funnel in there.”

Hille said that while some fill dirt will be added, the wildlife crossing will be about 19 feet tall from top to bottom.

“Every animal species has a minimum threshold for them to use these structures,” said Kreft, who also worked on a wildlife crossing near Williston that was designed to accommodate moose. “When people wonder why this structure is so big, we tell them that we want an openness factor. When an animal approaches the structure, we want it to look safe for them to go through. We don’t want an unsuccessful crossing nor does DOT. So, we put these wildlife crossings in locations and size them properly for the species we are trying to accommodate.”

Schonert agreed.

“It’s an arch type structure so when bighorn sheep are walking up to it, they can see through a little better than if it was a rectangle-shaped structure,” he said. “And then the new Long X Bridge will actually serve as a crossing as well. There will be open areas underneath the bridge span to facilitate wildlife movement.”

Wiedmann said a lot of time went into the design of the wildlife crossing, taking into consideration that bighorn sheep don’t like enclosed spaces.

“That’s why we had this unique design,” he said. “Open it up so those bighorns can see through. The key will be the fencing to funnel them to the crossing where they don’t have an option to cross the highway.”

After bighorns were removed north of Long X, what remains is a herd of about 50 animals in the area.

“That’s a pretty big herd,” Wiedmann said. “Typically, it’s 10-15 ewes east of the highway and 30 west, and the rams will migrate to this area during the rut. There is a lot of bighorn activity around here and because they don’t fear vehicles, it just makes it worse.”

Signs warning motorists that bighorn sheep frequently cross the highway in this area were put in place about a decade ago, but Wiedmann said the signs could only do so much.

“I’ve been here and watched big rigs lock up their brakes, smoke flying, because bighorns are crossing, or simply popped up out of nowhere,” Wiedmann said. “Another issue is when people see bighorns right off the highway and they stop right on Highway 85. I came down here once and there were like seven, eight vehicles stopped on the highway taking pictures. I actually fired a cracker shell to chase the bighorns away. That’s a real hazard if you have a big truck coming down the steep grade with people taking pictures of bighorns from their vehicles.”

Wiedmann said seeing an end in sight for the project is appreciated and long-awaited.

“It’s kind of eye-opening to me all the different agencies and individuals involved in this … it’s been quite a collaboration,” he said. “I know I’ve been working on it for about 10 years and it’s nice to finally see something happening.”

The view in the distance from U.S. Highway 85 near Long X Bridge. Quality bighorn sheep habitat is found on both sides of the highway.