Interstate 25 expansion south of Denver shows need for wildlife tunnels as officials track carnage

Bears, deer, bobcats, mountain lions and other animals are dying, picked off at the rate of at least one a day by vehicles, as Colorado contractors widen Interstate 25 south of Denver to six lanes through wetlands and other wildlife habitat.

Colorado Parks and Wildlife officials say this carnage along an 18-mile stretch between Castle Rock and Colorado Springs reflects an intensifying statewide clash caused by human population growth and demands for faster mobility.

Five wildlife crossing tunnels under I-25 — 16 feet high and 80 feet wide, costing $4 million to $6 million each — are planned in an effort to reduce the killing. But construction of these won’t begin until May, and may take months.

“We’re seeing at least a hit a day — deer and elk, mountain lions and black bear,” said Chuck Attardo, the Colorado Department of Transportation’s I-25 project environmental manager. “We’re going to improve this situation drastically. We’re expecting to reduce the animal-vehicle collisions by 90 percent.”

However, more animals almost certainly will perish until the wildlife crossings are installed, Attardo said. “Right now it is unavoidable.”

RELATED: Two sections of I-25 are going under the knife. Here’s what it means for you.

Around Colorado, vehicles collide with 3,405 wild animals a year on average, CDOT data show. State contractors have installed 55 wildlife crossing tunnels and at least one overpass over the past decade so that animals can move across habitat without getting hit. The I-25 widening between Castle Rock and Colorado Springs is the only current highway expansion in the state that will include designated wildlife crossings, CDOT spokeswoman Tamara Rollison said.

Colorado wildlife officials last year prioritized nine high-risk zones, including the I-25 corridor, where collisions with animals are most common.

Wildlife also die frequently in collisions along Interstate 70 (Floyd Hill, Mt. Vernon Canyon and Eagle); U.S. 285 (Morrison); U.S. 160 (Durango to Pagosa Springs and Durango to Mancos); U.S. 550 (north of Durango and from Montrose to Ouray); Colorado 82 (Glenwood Springs to Aspen); U.S. 36 (Boulder to Lyons); and Colorado 93 (Golden to Boulder)

Colorado Parks and Wildlife officials say properly built crossings are effective.

“In an ideal world, it would be awesome to have them everywhere. But it takes a lot of money,” agency spokesman Jason Clay said.

A photo of wildlife captured by ...
Image provided by Colorado Parks and Wildlife

A photo of wildlife captured by a Colorado Parks and Wildlife camera set up near the Interstate 25 expansion project south of Denver.

Co-existence with wildlife in Colorado has emerged as a difficult challenge amid population growth and a development boom concentrated along the Front Range. Wildlife habitat near cities gives safe space for some species. But as more habitat is fragmented by homebuilding, commercial expansion and road construction, wildlife needs for non-lethal connecting corridors increase.

“This is super important,” Clay said. “The animals are going to migrate where they need to go  — winter range, summer range. They’re going to go where they need to go to get their food. Wildlife crossings allow them to do it safely — a good step in the right direction. … The human population is continuing to grow. A lot of our wildlife is doing well. There’s got to be a balance there.”

The widening of I-25 between Castle Rock and Colorado Springs stands out because the highway cuts through relatively open land. The foothills west of I-25 lead into mountain habitat.

It is an area that the U.S. Fish and Wildlife Service has identified as critical habitat for the protected Preble’s meadow jumping mouse, an endangered species eradicated elsewhere along the Front Range. CDOT officials said they cannot tell whether any mice have been killed during the I-25 expansion, which coincides with construction of a 24-hour truck stop. Highway crews have placed downed trees and grass in their work zone to provide cover for mice.

For wildlife, the existing culverts under I-25 are proving too small, officials said, and animals migrating for food are effectively blocked unless they bolt in front of vehicles, construction crews and heavy machinery.

Remote cameras installed by Colorado Parks and Wildlife last May, to monitor the impact of widening I-25, are revealing bobcats, bears, deer, elk, turkeys and other wildlife wandering along the highway, searching for safe ways across. These 13 cameras are giving new insights into how animals respond when people build roads through their habitat.

A photo of wildlife captured by ...
Image provided by Colorado Parks and Wildlife

A photo of wildlife captured by a Colorado Parks and Wildlife camera set up near the Interstate 25 expansion project south of Denver.

State agencies documented 504 animals killed in collisions with vehicles along the 18-mile section of I-25 between 2005 and 2017. The data show vehicles killed 362 deer, 74 elk, 42 bears, six mountain lions, three foxes, three coyotes, two raccoons, two hawks and a bobcat among other species. Last fall, CDOT managers reported two mountain lion deaths among numerous wildlife fatalities following collisions.

Vehicle collisions rank among leading perils for wildlife in Colorado but generally aren’t the main cause of death.

For example, bobcats increasingly are hunted, driven by rising prices for pelts, according to CPW’s latest Furbearer Management Report. State data show hunters killed 1,811 bobcats in 2017, more than double the 680 killed in 2004. (The bobcat population appears stable overall statewide, CPW officials said, though counting bobcats, like lynx and mountain lions, can be difficult.)

In contrast, vehicle drivers and passengers usually survived I-25 collisions with animals. No drivers or passengers died in collisions between 2011 and 2016, a recent state study found. But 42 people suffered injuries and 264 vehicles were damaged — leading to an estimated annual economic cost of $1.2 million, the study found.

Building more wildlife crossing tunnels and overpasses “is great for wildlife and also good for the safety of our motorists,” Clay said. “They will pay for themselves over time.”

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