The question is being asked with an increasing sense of concern on the wildlife front: Why are mule deer populations gradually declining in Oregon?

Wildlife biologists at the Starkey Project are turning to hunters to help them solve this mystery.

The biologists are conducting a study at the Starkey Project seeking to determine why mule deer numbers are dropping. One potential cause they are looking at is a rising number of Rocky Mountain elk in Oregon.

Oregon’s Rocky Mountain elk population, according to the Oregon Department of Fish and Wildlife’s latest figures, is up 6 percent since 2013. The state had 74,227 Rocky Mountain elk in 2016, up 4,654 from 2013 when it had 69,573.

ODFW statistics also indicate Oregon had 226,775 mule deer in 2016, down 4,466 from 2013 — and down a whopping 20,575 from 2004. Over the same time, mule deer have been declining throughout western North America, according to ODFW.

Biologists suspect that rising elk numbers could be having a detrimental impact on mule deer because they appear dominant when in the same locality, said Mike Wisdom, the Starkey Project’s lead scientist. This may mean elk always get the vegetation and living space they prefer at the expense of deer.

“Elk push (mule deer) to the margins,” said Wisdom, who is also the U.S. Forest Service project leader for the Starkey Project.

To determine if the domineering nature of elk is harming mule deer, Starkey Project biologists are preparing to trim the number of elk in their enclosure from 350 to about 100 with the help of hunters. The amount of tags issued for hunts in the Starkey Project enclosure will significantly increase in 2019.

“Ideally we will have 100 elk (after the 2019 hunts),” said Darren Clark, Oregon Department of Fish and Wildlife project leader for the Starkey Project.

The Starkey Project’s staff will then determine if the reduction in elk is impacting the health and population level of mule deer at the study site. They will do this by comparing pregnancy rates, winter fawn survival and body composition of mule deer before and after the elk herd was reduced.

Relying on data from radio collars, biologists will also be able to determine if the movement patterns of mule deer are influenced by the reduction in elk. Clark said elk prefer isolated areas far from people and appear to push mule deer out of these areas, which may mean the smaller animals end up closer to forest roads, which is not a safe place.

“They are more vulnerable to poaching and road hunting (during hunting seasons) and can be hit by vehicles,” he said.

Mule deer may also suffer when pushed out of preferred habitat by elk because the area they want to be in may contain shrubs and other vegetation that are more nutritious than that found in other areas.

“We have all of the area mapped for nutrition,” Wisdom said.

Predation is another possible factor in the declining mule deer population being examined by Starkey Project biologists.

Predation will be studied with help of radio collars attached to mule deer and predators and cameras in the Starkey enclosure. The collars and cameras will allow researchers to determine when a deer has been killed, so they can get to the kill site soon after an attack and find evidence revealing the reason for the deer’s demise.

“If we can get to the site in a day, we will be able to determine the cause of death,” Wisdom said.

Predators known to take mule deer in the Starkey Project include cougars, coyotes, black bears, bobcats and wolves. Wisdom said these predators have no trouble going over or under the Starkey Project’s eight-foot fence.

Of the mule deer predators coming into the Starkey Project, wolves are among the least common.

“We have wolves in there less than 10 days a year,” Clark said.

Wisdom said when the elk population in the Starkey Project enclosure is reduced, researchers will be watching closely to see if this will cause predators to attack mule deer there more frequently.

Predators are not the only enemy deer face. Clark said he has seen two fawns that were stomped to death by elk.

“Elk can be very aggressive when dealing with other animals,” he said.

Predation, nutrition and elk are being looked at separately as part of the mule deer decline study, but Clark said it may be found that none of them alone is the culprit.

“It may be that the reason for falling mule deer numbers is a combination of all three,” he said.