To shoot, or not to shoot, at Rocky Mountain NP


By Larry Keller, 05-17-2011

 The elk of Rocky Mountain National Park are wildlife’s couch potatoes. Rather than roam widely throughout the 415-square-mile park and the land outside it, they are content to laze around in meadows, eating, sleeping and mating.

With no predators, they can afford to be slackers. Many of them saunter into the tourist town of Estes Park outside the eastern entrance. There, they mosey along city streets and loiter on golf courses.

Their inertia has created Rocky Mountain NP elkproblems in the park, however. Aspen and willow stands are denuded where the elk do much of their grazing. That habitat is vital to a variety of birds and butterflies, park officials say. The damage has also driven out most of the beavers that once populated the area, which in turn has caused a nearly 70-percent decline in surface water that helps nourish the very habitat being damaged.

After years of debate, Rocky Mountain National Park decided on a solution: Kill a portion of the voracious ungulates. It’s not an image coveted by the National Park Service – sharpshooters picking off the park’s most iconic creatures. The killing is done at dawn in winter with rifles equipped with sound suppressors.

There is, however, a nonlethal method that can potentially keep the elk in check and lessen the need to kill them: Birth control. In January, a team of researchers wrapped up a three-year field study in which dozens of cow elk were injected with a vaccine called GonaCon designed to prevent pregnancies. The vaccine worked well for up to two years. But is wildlife contraception a viable tool in controlling proliferating wildlife herds? If it is, it might also be one means of managing the size of rapidly-breeding wild horses in the West and nettlesome bison at Yellowstone National Park.

“I’m always very wary when we try to do Mother Nature’s job better than she does,” says Jenny Powers, a National Park Service wildlife veterinarian and one of three lead scientists who participated in the elk research.

But Stephanie Boyles, a wildlife scientist with the Humane Society of the United States, welcomes the prospect of family planning for elk. “As stewards, we are called on to do something to keep (wildlife) in balance with nature,” she says. “It’s a politically contentious area.”


Elk are native to the Rocky Mountain National Park area, but unregulated hunting wiped them out by the 1870s. Their only significant predators were wolves, and they were eradicated by 1900. Elk were reintroduced in 1913 and 1914, and the national park was established in 1915. Congress banned hunting within the park in 1929. The elk population quickly grew – so much that the animals decimated parts of the park’s vegetation. Between 1944 and 1969 park rangers culled some of the elk to keep their numbers more manageable. (Culling differs from hunting in that it’s not recreational and there’s no element of a fair chase.)

In 1969 the park began a “natural regulation policy” in the belief that hunting of elk outside the park would control their numbers inside it. That didn’t happen, in part because the park’s herd is less migratory and more concentrated than under natural conditions. Many of the elk spend winters in the eastern part of the park, where their munching has damaged some aspens to the point where they don’t grow back.

Park officials say the optimum population within the park is between 600 and 800. Between 1997 and 2001, the park estimates there were between 2,800 and 3,500 elk within the boundaries. There also are another 1,000 to 1,300 elk that winter outside the park.

The park began a $6-million, 20-year plan in 2008 to reduce the elk population and restore the plant life it damaged and destroyed. The plan calls for “gradual lethal reduction” and fencing around some of the most badly-damaged aspens and willows, while leaving open the options of fertility control and wolves.

Four alternatives were considered, including one that would have culled far greater numbers of elk in the park, and another that would have phased in a maximum of 14 gray wolves. The thinking was that the wolves would kill some of the elk and scare others into dispersing elsewhere in the park. Their grazing would then be over a wider area and be less destructive. Yet another alternative would have been the use of “fertility control agents,” but even doing this would have still required some culling to keep the elk’s numbers at an acceptable level.

Elk have now been culled inside the park three years in a row. Park service personnel and others, including 23 trained volunteers who get $7 a day to cull the elk, do the job. Some 122 females and one male that had the bad luck to be mistaken for a female have been killed in the past three years. (Seventy-nine of them of them were euthanized during the contraception research, while the remaining 44 were culled, according to Kyle Patterson, the park’s spokeswoman.)

That’s far less than the maximum of 200 animals a year that park officials had said might have to be culled. Patterson cites a couple of reasons. A historic snowstorm in 2003 caused many of the elk to migrate out of the park toward the city of Loveland 30 miles to the east. And there was a record hunting harvest outside the park in 2006. All of that can be reversed with a series of mild winters or if the Loveland vagabonds return.


GonaCon was developed in the early 1990s by Lowell Miller and other scientists at the National Wildlife Research Center, the research arm of the United States Department of Agriculture’s Animal and Plant Health Inspection Service in Fort Collins, Colo. Sitting on 43 acres in the foothills, the center’s mission is to mitigate human-wildlife conflicts, whether by nonlethal or lethal means. Its work includes conducting research into reducing bird and aircraft collisions, developing nonlethal ways of lessening wildlife damage to forests and analyzing toxic concoctions aimed at killing tiny, nonnative coqui frogs in Hawaii.

GonaCon is registered by the U.S. Environmental Protection Agency for use on female white-tailed deer. The vaccine has also been tested on other animals, including Yellowstone bison, feral cats and dogs and California ground squirrels. Federal scientists also partnered with a private company on an oral contraception for use on urban Canada goose and feral pigeon populations, and are working on an oral contraceptive for feral hogs.

GonaCon works by stimulating the production of antibodies that reduce the ability of a hormone called GnRH to trigger the release of sex hormones. Females don’t go into heat and males aren’t amorous as long as there are sufficient levels of antibodies in the female’s body.

The Rocky Mountain National Park elk were vaccinated in the daunting cold of January 2008. First, the animals had to be shot with a tranquilizer dart – not easy on mornings when the drug froze inside the dart. The dart guns are accurate up to 45 meters, says Powers, the park service veterinarian. “The habituation of these animals and their fearlessness of humans made this possible,” Powers says. “There are very few (elk) populations close enough to dart them with a tranquilizer.”

Once sedated, the elk were rolled on to their chests so they could breathe easier, blindfolded, injected with the vaccine and fitted with a radio telemetry collar to locate them later. Samples of blood, feces and hair were extracted. Then they were injected with another drug to reverse the effects of the tranquilizer. The entire process took about 40 minutes, Powers says.

None of the critters died while being treated or examined, but one did give researchers a surprise when she got to her feet. Normally, elk bolt in the direction away from the scientists when they come to. “But this animal seemed disoriented and chased my colleague around and around the willow,” Powers says.


Elk that were subsequently recaptured were checked not only for pregnancy but chronic wasting disease, a transmissible, untreatable and fatal neurological disorder also found in deer. Hunters outside the park were asked not to shoot at elk wearing collars, and animals treated with GonaCon wore tags advising hunters not to consume their meat since the vaccine may not have cleared their bodies.

One year after injecting 60 Rocky Mountain National Park elk with GonaCon, 10 of the animals were recaptured. None was pregnant. Yet 90 percent of the control group recaptured – also composed of 60 females given a saline solution—were pregnant.

Powers declined to provide data for the animals recaptured after the second and third years until she and her colleagues publish the results in a scientific journal. But she says the vaccine, while still effective after the second year, was less so than after year one. And after three years, the percentage of pregnancies was greater than after two years. (In a small study of captive elk between 2004 and 2007, females injected with GonaCon actually were more infertile with each passing year. The percentages were 86, 90 and 100 percent in one group, and 90, 100 and 100 percent in a second group given a stronger dose of vaccine).

Powers thinks GonaCon might be effective in free-roaming elk for a year or two, but she’s equivocal about its potential. Some animals that have been treated may leave the park and never return, while others living outside the park – like the Loveland emigrants—may return, she says. Those sorts of variables dilute GonaCon’s effectiveness. She also points out that determining how much impact a contraceptive has on reducing a herd’s numbers is imprecise because severe weather and deaths from chronic wasting disease kill an undetermined number every year.

She’s not alone in her guardedness. “It’s just a bit too early to tell where we’re going to go next,” says John Mack, the park’s branch chief of natural resources. “We need to wait and be patient.”

Every one of the elk in the GonaCon study had an abscess at the injection site, Powers says. The researchers found nothing to suggest that the sore spots became infected, hindered them in foraging or made them lame. Nor were they aware of behavioral changes caused by the vaccine. Since they didn’t monitor the elk year-round, they just don’t know. “Free-ranging wild behavior with GonaCon has not been answered,” Powers says.

Still, there is reason to believe that wildlife contraception may become a more common method for controlling wildlife populations. Another contraceptive, Porcine Zona Pellucida or PZP, has been field-tested for nearly 30 years. The Bureau of Land Management, in cooperation with the Humane Society of the United States, is treating nearly 900 mares from wild horse herds in Idaho, Nevada and Utah this year in an effort to control that species.

Unlike GonaCon, PZP doesn’t have to be injected manually, says Stephanie Boyles, the Humane Society wildlife scientist. Wild horses are drawn to temporary corrals baited with food or water, injected by a dart containing the PZP and released. That’s a big improvement over the BLM’s current program of rounding up frightened horses by helicopter and confining them in holding pens, Boyles says. “The technology continues to get better and better all the time,” she adds.

Even Congress has taken notice. In February, Rep. James Moran, D-Virginia, called the BLM’s use of holding pens for wild horses “enormously wasteful and misguided” and said contraception would be cheaper and more humane.

Skeptics, however, question whether contraception should be used on wildlife at all. When public input was solicited on various proposals for dealing with the elk and the damage to their habitat, some people were “strongly in favor of fertility control, and some were strongly opposed who felt it was unnatural,” Patterson says.

“Some things are meant to be wild,” Powers says. “At some point, do we not want to treat them like domestic animals and be handling them? I think it’s important to point out that this is no silver bullet so that we don’t have to kill wild animals. Any time we’re manipulative with wild animals, we’re messing with natural selection.”

Boyles counters, “Any intervention could be construed as tampering with the natural process”—including culling. “If that’s not animal husbandry as well, I don’t know what is.” The reason there are wildlife imbalances, she notes, is because humans eradicated predators, such as at Rocky Mountain National Park.

Powers agrees. “We’ve changed the ecosystem,” she says. “We’ve created an artificial situation.”

Few argue that free-ranging wildlife populations can be reduced by contraception alone. Its best use may be with animals that are confined to some extent by either geography or fences, Powers says.

“It probably is more valuable in a confined setting than an open setting,” Lowell Miller, the lead researcher in the development of GonaCon, says of that vaccine. “It’s a lot more work (in an open setting), but it can be effective. I think as time goes on, we’ll determine how practical a tool it is.”

For more information on wildlife contraceptives, check out HCN writer Emilene Ostlind's pieces on wild horse contraceptives and general contraceptives for a variety of wildlife.

Essays in the Range blog are not written by High Country News. The authors are solely responsible for the content.

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Image courtesy Flickr user Wally Gobetz

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