The state of Colorado recently decided to spend $4.5 million over the next nine years killing cougars and black bears to see how this might affect mule deer numbers. The effort, which begins in the spring, allows the Colorado Parks and Wildlife Commission to trap and euthanize up to 15 mountain lions and 25 black bears each year in the Piceance Basin, a region in the northwestern corner of the state known for its natural gas deposits.
Ever since pioneers first struck gold in Colorado in 1859, the state’s mule deer have faced numerous setbacks. First, the sudden influx of fortune seekers overhunted the deer. As the settlers laid down roots, their grazing livestock then outcompeted the deer for food, and finally, the development of homes, ski resorts, and extraction industries pushed the species to the fringes of the wilderness. Despite the mule deer’s modest rebound in recent years, the state’s wildlife biologists say the herd is only at about 80 percent of what it should be.
As for the predators, the CPW estimates the cull will represent 1 percent of the region’s mountain lion population and 2 percent of its black bears. Since mountain lions and bears prey on mule deer (and are especially fond of fawns), the agency thinks that having fewer of these hungry mouths might let the herd bounce back faster. But here’s where that idea gets sticky.
The Science of Predator Control
Decreasing predator numbers in order to relieve prey populations sounds simple enough, but Barry Noon, an ecologist at Colorado State University, says there’s a fundamental problem with his state’s current strategy. “The consensus in the literature is that predation is a very minor factor in controlling mule deer populations,” says Noon.
Take this 2016 study, which challenges the idea that mountain lions drive down mule deer numbers by showing that such predation is compensatory rather than additive. In other words, the deer being killed would likely have died anyway, from starvation or disease. This is because mountain lions usually prey only on animals that are already in bad shape, the study found.
And research from 2012 reviewed seven studies that looked at what happens to mule deer when you remove their predators from an ecosystem. Here, too, the authors found almost no evidence suggesting that predation was limiting deer populations. (While one of the studies showed that wolves directly affected a deer population on Canada’s Vancouver Island, islands aren’t always representative of what happens in mainland ecosystems.)
“The takeaway is that we didn’t see any evidence for predator control boosting deer populations,” says Tavis Forrester, the review’s lead author, who is now a carnivore biologist for the state of Oregon. (Note: His opinions don’t necessarily reflect those of the Oregon Department of Fish and Wildlife.)
The studies evaluated predator controls involving coyotes, mountain lions, and wolves, but according to Forrester, there really isn’t any good research on what happens to mule deer numbers after you kill black bears. The bears are known to prey heavily on deer fawns within their first two weeks of life.
If Not Predators, What Else Could Be Keeping the Deer Down?
Lots of things could be responsible for depressed mule deer numbers. Noon points to broader factors such as reductions in habitat quantity, quality, and connectivity. Just as predators need prey to survive, prey animals need their own food sources. If there isn’t enough land on which to safely forage, mule deer won’t thrive regardless of what other survival factors are present.
Colorado’s human population has increased more than sixfold in the past 100 years or so. And where there are more people, there are bound to be more roads and development. Even the state’s backcountry, where homes are less likely to spring up, has seen a rapid uptick in development thanks to the natural gas boom. Between 1989 and 2012, Colorado added 27,000 gas drilling wells. More wells means more roads, more trucks, more noise, more people.
While these habitat issues occur throughout the state, the CPW says it didn’t seem to apply to the two study areas in the Piceance region. Scientists conducted extensive research in this area, says Lauren Truitt, the agency’s spokesperson, and found that neither habitat destruction, the energy industry, nor residential development seems to be curtailing the mule deer population.
And while three out of the four mule deer herds in the Piceance Basin are slowly increasing, Truitt says the overall population in this region is still just a third of what it was in the 1980s. To help give the deer’s numbers a boost, the CPW has lowered the number of buck hunting licenses available in the Piceance region by more than 85 percent since 2007 and essentially eliminated doe hunting, since females have the biggest impact on reproduction rates. During this time, fawns also had high birth weights and low starvation rates. All of these factors brought suspicions back to the predators.
Could predators be putting heightened pressure on the Piceance mule deer? “Sure, it’s possible,” says Noon. “But is it the key driver of [population] dynamics in mule deer in the southern Rocky ecosystem? No, it’s not. Does that justify spending $4.5 million?”
Noon says the decision to kill mountain lions and black bears in favor of deer smacks of catering to the state’s hunters. And get this: Along with bears and cougars, it’s perfectly legal to hunt mule deer in the state of Colorado. Hunting license fees, in fact, generate 62 percent of the CPW’s revenue.
Truitt calls this a “user-paid, user-benefited funding model,” with hunters, anglers, and visitors funding the state’s parks and wildlife programs.
All of this creates an inherent conflict of interest, says Noon. “If you’re making a choice to kill one species to the benefit of another, then that’s a very clear and direct statement that deer are more important than mountain lions and black bears,” he says. “Now, why is that?”
The CPW makes no bones about needing more money to conduct its duties. Colorado’s wildlife budgets have seen $50 million worth of cuts since 2009, and the agency has lost funding for around 50 positions. Programs have also been cut, including initiatives supporting wetlands and the Aquatic Nuisance Species program.
Like it or not, the predator cull study will be in the works until 2026. For what it’s worth, Forrester says Colorado has one of the most robust research programs of any state agency he knows of, with the capacity to do some high-quality science. So if anyone can get to the bottom of predator-prey relations in the Piceance, it’s likely to be the CPW. But in the face of dwindling budgets, the question remains: Is killing cougars and bears really the best use of 4.5 million big ones?
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