GRAND JUNCTION — In the face of continued decline in the mule deer population throughout much of Colorado and the West, wildlife managers, sportsmen and conservation organizations are in search of the smoking gun.

And at least a few of them would like to aim it directly at the predatory coyotes they perceive as the gravest threat to the once-thriving herds.

“Everybody is trying to do stuff for habitat, but the population is still going down. I would ask you to really consider looking at all fronts, predator control, anything that we can do to help bring our deer population back,” Colorado Mule Deer Association field representative Denny Behrens said while addressing Colorado Parks and Wildlife Commission members last week. “We would ask that you really take a hard look. The state of Utah will be spending over $1 million on coyote control over there — $50 for a bounty. That sounds in this state like something that can’t happen. Well, what are we going to do? Gentlemen, ladies, we’ve got to do something to bring our deer back. We need to look at all issues.”

“There’s no single cause”

Colorado’s waning mule deer population is no stranger to scrutiny, however. As wildlife managers established big game hunting license quotas for the forthcoming fall seasons at Thursday’s monthly meeting of the PWC, the majority of time was spent discussing the mule deer dilemma. A roughly 6 percent statewide cut in the licenses allotted was not drastic enough for some, even as doe hunting opportunities amid the state’s largest deer herd have shrunk by 94 percent over the past five years. Buck licenses in the same unit in northwest Colorado have been reduced by 78 percent in that span.

“We’ve been taking large measures to reduce harvest in some of these herds that are declining,” said Andy Holland, big game manager for Colorado Parks and Wildlife. “But despite drastic reductions in a lot of these license numbers, herds continue to decline, which tells us that license numbers are not driving these declines.”

The obvious question then: What is driving the collapse? “There’s no single cause,” Holland said. “Between severe winters, increased development, habitat decline and migration corridor fragmentation, most Western states are seeing declines in mule deer populations. We adjusted license numbers accordingly.”

Wildlife managers will issue 79,800 limited deer licenses this fall, 65,100 of them in units west of Interstate 25, with a post-hunt objective of 425,000 deer statewide. The current population estimated at 418,000 deer is down from 430,000 a year ago, putting about half the state’s Data Analysis Units below objectives.

The downturn is not unique to Colorado. Utah and Wyoming have seen similar declines. The Utah Wildlife Board has reduced the number of general season deer tags by 7,500 since 2011. And, as noted in Behrens’ plea, Utah has decided to take a more radical approach to the problem, recently passing legislation known as the Mule Deer Protection Act that appropriated $750,000 toward predator control targeting coyotes.

More habitat can only help

While it has been widely reported that coyote bounties will increase to $50 a head in July, the Utah Division of Wildlife Resources says details of the bounty increase have not yet been finalized. The Salt Lake City-based Mule Deer Foundation, however, has contributed an additional $100,000 to the division over the past two years to increase predator control on coyotes the group perceives as a primary threat to population objectives.

“The mule deer herds in Utah have continued to decline despite over $64 million being put toward habitat improvement projects over the last five years,” MDF president Miles Moretti said in a statement.

But the CPW’s Holland isn’t buying into the predator argument. Ultimately, he believes the amount of quality habitat available to mule deer remains the key, especially in winter.

“Certainly predators kill deer. There’s no question about that,” the Durango-based biologist said. “But I feel like there’s a pretty compelling case to be made based on the science in Colorado and surrounding Western states with sagebrush ecosystems that, even though coyotes do kill deer on winter range, unless you have the habitat to support a higher number of deer, you don’t necessarily end up with more deer at the end of the winter.

“And that’s because a deer that’s, say, malnourished is more susceptible to predation. We’ve done experimental studies where we manipulate coyote density and deer density, and if you kill coyotes, you certainly lower the predation rate on mule deer fawns. But the malnutrition rate and starvation rate goes up, and at the end of winter, you still end up with the number of deer that the habitat can support.”

Holland doesn’t rule out some as-yet undetected disease as a potential piece of the puzzle, and his team is studying the issue. He notes that other herds across the state, including those on the Eastern Plains, in Middle Park and the Gunnison Basin, are thriving as herds farther west decline.

Scott Willoughby: 303-954-1993 or swilloughby@denverpost.com