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DENVER (KDVR) — A recent study by a Denver nonprofit links development to the drastic decline of elk in two herds near Vail and Aspen.

“You may see elk on the road,” ecologist Paul Millhouser of Rocky Mountain Wild said. “Those elk are actually experiencing a lot of stress.”

Millhouser was tasked with investigating why two herds in the Roaring Fork and Eagle Valleys have dropped in numbers by 50 percent since 1999.

“We are in a little bit of danger of loving these places to death,” Millhouser said.

Milhouser says development tends to occur in valleys, an area elks prefer in the winter months due to lower elevation.

“They’re under stress, they’re burning more calories, they’re spending more of their time being alert and looking for danger and less time feeding,” Millhouser said.

He also says elk can be viewed as a “keystone species” and often indicate how healthy other wildlife in the area are.

“The same factors that are effecting elk, are effecting a lot of other species that we may not think about as much,” Millhouser said. “But are actually critical to the habitat surviving.”

Millhouser says herd rates that he has studied have been level recently, however he warns a “trigger event” such as a harsh winter could hurt elk populations as the animals are now less resilient.

For people concerned, he suggests contacting local elected officials about the issue.