Elk are crafty creatures. Just ask any elk hunter.
The big animals will hide in thick timber where a shot is impossible during the day, and then wander out into wide open meadows to feed at night when hunting isn’t allowed. The tactic may be frustrating for hunters, but it’s life-preserving for elk.
“We forget that elk are really savvy,” said Dan Stahler, Yellowstone Cougar Project manager.
Now a recently published study based on information collected in Yellowstone National Park shows that elk use much the same behavior to avoid mountain lions and wolves.
“It’s really a testament to elk as a species and how well they can manage risk,” Stahler said.
Mountain lions are known to inhabit rough, rocky, timbered terrain, but they mainly hunt at night. Wolves are more likely to hunt in open country in the early mornings and evenings. By spending days in the timber and nights in the open fields, elk are more likely to avoid being eaten by two of their main park predators.
“This study highlights that mechanism, how elk can select for the habitats they need,” Stahler said.
Stahler helped co-author the study of elk response to cougar and wolf predation in the scientific journal “Ecology Letters.” The paper is titled “Do prey select for vacant hunting domains to minimize a multi-predator threat?” The study says yes.
The research was based on long-term data from the park's wolf and elk monitoring programs and biologist Toni Ruth's cougar research conducted between 1998 and 2006 in Yellowstone.
The team revisited GPS data from 27 radio-collared cow elk that had been collected in 2001-2004 when the populations of wolves and cougars were higher. Utah State University biologists Michel Kohl and Dan MacNulty combined the elk GPS data with information on the daily activity patterns of GPS-collared cougars and wolves and the locations of cougar- and wolf-killed elk to test if elk avoided the predators by selecting for “vacant hunting domains,” places and times where and when neither predator was likely to kill elk.
“They were using risky places at safe times,” Kohl said.
“They have evolved adaptations that help them coexist with” many predators, he added.
"Had we ignored the fact that these predators were on different schedules, we would have concluded, incorrectly, that avoiding one predator necessarily increased exposure to the other," said MacNulty, an associate professor in Utah State University’s Department of Wildland Resources and Ecology Center, in a press release. "Movement out of the grassy, flat areas and into the forested, rugged areas to avoid wolves did not result in greater risk from cougars and vice versa because these predators were active at different times of the day."
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Although the GPS data set for cougars was small — six collared lions — Kohl said the information provided some interesting insights into where and when the big cats were hunting. As predicted, the cats were largely hunting at night, Kohl said, but the patterns were slightly different between males and females.
Understandably, females with kittens weren’t moving as much. Mobile big male cougars’ presence, however, often prompted an elk response.
“First and foremost, we showed that elk were responding more to cougars than wolves,” Kohl said. “There wasn’t much difference between their response to female lions and wolves.”
That’s likely because male lions are bigger, tougher predators than females, weighing in at 145 to 170 pounds when fully grown. Adult females typically weigh between 85 and 120 pounds.
Kohl said it will be interesting to see what the current Yellowstone cougar study reveals on the topic, since some of the cats are carrying accelerometers that will provide more detailed information on cougar hunting tactics.
“We can see where they are stalking prey, when they make a big pounce,” Stahler said. “Essentially this new technology allows us to accurately estimate their kill rate,” along with the cougar’s caloric expenditure, giving the researchers an “energetic profile” of lions on the landscape.
The ongoing study has already documented cougars shifting more of their diet to mule deer, Stahler said. Whereas elk used to supply about 65% to 70% of the mountain lions’ diet, it’s now closer to 50%.
Stahler, who renewed the study of cougars in the park in 2014, said that Kohl’s published study “reminds the public and us as biologists that there is an equally important predator on the landscape,” a fact that was somewhat overlooked after wolves began being reintroduced to the park in 1995. Because the wolves were so easy to see and study, they dominated scientific discussions and studies. The big canines also became iconic representations of Yellowstone for park visitors.
“We have to remember there are other predators out there,” Stahler said.
That point was driven home in a three-year study of elk predation in the Bitterroot Valley from 2011 to 2014. Although area hunters believed a growing population of wolves was responsible for declining elk populations in the West Fork of the Bitterroot, the Montana Fish, Wildlife & Parks study instead showed lions were the bigger predators, largely of elk calves.
"Wolves are often the presumed or blamed predator for any change in a prey population, numerical or behavioral," said Doug Smith, who leads Yellowstone’s wolf program, in a press release. "Our research shows that this is not necessarily true, and that other large predators in addition to wolves need to be considered."
Kohl and MacNulty co-led the study, published in Ecology Letters, with Toni Ruth (Hornocker Wildlife Institute and Wildlife Conservation Society), Matt Metz (University of Montana), Stahler, Smith, and P.J. White (Yellowstone National Park). Their work was supported, in part, by the National Science Foundation, Ford Foundation, and Utah State University as part of Kohl's doctoral research.