Faced with a rapidly dwindling deer population, Colorado wildlife officials are proposing to kill more mountain lions and black bears — a “predator control” push aimed at saving fawns.

The proposal reflects growing worries about deer, which are crucial for the hunting industry and Colorado Parks and Wildlife (CPW) revenues. The statewide population is 110,000 short of the 560,000 deer that wildlife managers deem optimal for the state.

But targeting lions and bears to try to boost deer is highly controversial. The Humane Society of the United States is rallying opposition to predator control, arguing that Colorado’s approach will orphan bear cubs and lion kittens who then would starve, be eaten or die of exposure.

“It won’t work,” Humane Society carnivore protection manager Wendy Keefover said.

“There are lot of things causing mule deer decline in Colorado and the western United States, but it is not predators. Predators and prey have lived together for eons. What’s killing off the deer? Humans. We’ve turned their winter range into housing development or oil and gas well pads and roads, which leads to collisions. And we have more killing of deer by hunters.”

The National Wildlife Federation, a hunting and conservation group, emphasizes habitat loss and fragmentation as a primary cause of the decline of Colorado deer. And state biologists have determined that oil and gas drilling in deer habitat is hurting the ability of deer to recover.

CPW hasn’t taken a position on a federal Bureau of Land Management plan to allow up to 15,000 new oil and gas wells on prime deer habitat in northwestern Colorado.

“It is quite common for multiple factors to be acting simultaneously on mule deer and for the impact of those factors to vary annually, seasonally and geographically,” CPW spokesman Jerry Neal said in an e-mailed response to queries. “We rarely address the ‘should’ question. We primarily address the ‘how to’ question.”

A look at state data found that hunters in Colorado kill up to 1,364 bears and 467 mountain lions a year, more than in other western states and double the numbers a decade ago. Colorado ranked third, behind Idaho and Montana, with hunters killing 3,414 mountain lions between 2005 and 2014.

The Colorado wildlife managers lack solid estimates for statewide mountain lion and bear populations because these animals are hard to count. CPW has estimated the bear population at 17,000, based mostly on extrapolations, and the lion population at 4,500. There’s no way to know, CPW officials have said, whether statewide mountain lion and bear populations are increasing or decreasing.

State data on mule deer show the statewide population has decreased from 614,000 in 2005 to 450,000 — well below the target population of 560,000.

That decline has prompted cuts in the number of deer-hunting licenses issued by the state. The number issued in the Arkansas Basin area where lions and bears would be targeted was cut from 2,840 in 2010 to 2,475. The number issued in the northwestern Colorado area where lions and bears would be targeted was cut from 28,350 in 2007 to 4,360.

The CPW predator control push would start this winter. State wildlife managers first would focus on a 3,478-square-mile area near Salida in the upper Arkansas River basin. Then, in spring, they’d expand the predator control experiment to a 493-square-mile area near Rifle in the Piceance Basin of northwestern Colorado.

They propose to kill up to 15 more lions and 25 more bears a year, according to CPW documents. The killing would be done during spring when fawns are most vulnerable. The goal is a significant impact on deer survival.

Predator control would happen only in areas “where we have evidence that predation may be the primary limiting factor for mule deer,” Neal said. “We want to test that assumption.”

A decision by state wildlife commissioners is expected by Dec. 15.

If the commissioners vote yes, state wildlife crews would use cage traps, culvert traps, foot snares and hunting dogs to immobilize mountain lions and bears. Then those caught would be shot.

A final update of the BLM oil and gas plan for northwestern Colorado includes proposals to reduce impacts on wildlife. But conservationists and hunting groups still raised concerns about the wisdom of allowing drilling in the heart of critical deer habitat.

While state biologists agree oil and gas development hurts deer, CPW officials have not opposed the plan to allow up to 15,000 new oil and gas wells near Rifle.

However, CPW did assert, in a Sept. 7 letter to the BLM from northwestern Colorado regional manager Ron Velarde, that winter range is essential for deer. Velarde recommended restricted oil and gas activity between Dec. 1 and April 15.

It was unclear how impacts of predator control on lion and bear populations would be measured.

“The decline of mule deer in western Colorado is a complex issue with many potential causes, which may include predation,” NWF regional director Brian Kurzel said. “We encourage Colorado Parks and Wildlife to take a scientific approach to wildlife management that includes multiple strategies and focuses on the greatest issues at hand, including what we see as a primary factor – the quality and quantity of habitat.”