Stress from wolves may not be the reason behind a declining elk population near Cody, according to a study published today. The conclusion stands in contrast to previous research, which held that increased stress from wolves was behind a drop in the number of elk in the Yellowstone area.
The presence of wolves doesn’t dramatically change the way elk behave, said Arthur Middleton, lead author of the paper published in the journal “Ecology Letters.” Earlier research suggested the mere presence of wolves stressed or scared elk so much that they moved large distances, hid in trees, and then became so unhealthy they lost pregnancies or simply couldn’t get pregnant.
Migratory elk in the Clark’s Fork Herd near Cody moved slightly when wolves came nearby, but not enough to change their eating habits, make them lose weight or prevent them from becoming pregnant, Middleton said.
The paper, “Linking anti-predator behaviour to prey demography reveals limited risk effects of an actively hunting large carnivore,” is one of three published by Middleton following an extensive study completed while working in the Wyoming Cooperative Fish and Wildlife Research Unit at the University of Wyoming. The study was backed by more than a dozen government and nonprofit organizations including the Wyoming Game and Fish Department, Wyoming Animal Damage Management Board, U.S. Fish and Wildlife Service, Boone and Crockett Club and Safari Club International.
Middleton’s second paper from the study, published in the journal “Ecology,” found that drought and calf predation by grizzly bears were key factors behind the declining elk calf numbers. Wolves do eat adult elk, Middleton found, but not enough to significantly reduce elk numbers in the Clark’s Fork Herd.
“It’s fascinating to fund the research and let the chips fall where they may,” said Tom Toman, director of science and planning for the Rocky Mountain Elk Foundation, a leading sportsman organization, which helped fund the study.
“I am glad we have an objective look. It’s better to know exactly what’s going on other than anecdotes.”
Drops in elk calf ratios
Middleton started the study because migratory elk in the Clark’s Fork Herd saw drops in elk calf ratios starting in the mid-1990s and have remained low since 2002.
The migratory herd also had far fewer pregnancies than the elk in the herd that stayed near Cody year-round. Pregnancy rates for migratory and residential elk herds were historically equal.
Middleton and other biologists put GPS collars on both elk and wolves to observe the animals’ interactions. They spent more than three months each winter for three years monitoring the animals’ behavior.
They found wolves encounter elk relatively infrequently, and when they do, elk don’t respond dramatically, said Middleton, who is now at the Yale School of Forestry and Environmental Studies.
About 100 migratory elk moved through the Sunlight Basin area for every one wolf during the study. Ultimately, elk encountered a wolf on average every nine days. When they did interact, elk only seemed to react when wolves came within about half a mile. Elk increased their movement on average about 30 yards per hour in response.
It would be as though a bully sits down next to you in the lunchroom and you move to the next seat or the next table but continue eating. You don’t jog to the next town or hide, Middleton said.
The body fat of elk that interacted with wolves the most was the same as elk who had few wolf interactions, Middleton found.
People have likely seen wolves dramatically scatter herds of elk, but taken as a whole, wolf presence doesn’t have a significant impact on elk health, he said.
The results confirm what Cody Game and Fish biologist Douglas McWhirter believed. Elk, even in areas with high numbers of wolves, haven’t shifted to new areas, he said. Wildlife managers have cut back significantly on hunting licenses, and while calf survival is low, adult elk survival has been high.
If wolves’ presence doesn’t shift elk to new territory or prevent them from getting pregnant, then they also may not be the cause of the increase in willows and aspen in the Yellowstone area, as previously believed, he said.
“Even if wolves play a role it’s likely considerably smaller than we thought,” Middleton said.
Willows and aspen have improved, which is likely because all large carnivore numbers have increased in northwest Wyoming, especially Yellowstone National Park, resulting in an overall decrease in elk numbers, said Doug Smith, senior wildlife biologist with Yellowstone National Park.
Wolves and mountain lions eat elk and bears feed on elk calves. Fewer elk means fewer mouths to feed, which means more vegetative growth, Smith said.
People tend to blame wolves for everything, such as scaring elk into not becoming pregnant, or give them credit for everything, such as improving the greater Yellowstone ecosystem, said Mike Jimenez, wolf management and science coordinator for the Fish and Wildlife Service.
“Wolves are not that bad and not that good, they’re another part of wildlife,” Jimenez said. “As research goes on, that’s the part that’s so helpful. Wolves take their place like other predators or other parts of the ecosystem.”