Hunting The Hunters -- Reintroduced Wolves Killing Mountain Lions

Environment. The reintroduction of wolves in various habitats has prompted scientists to study animal behavior in altered ecosystems. One study of wolf-mountain lion interaction in Montana provided some surprises.

There are predators and there are the animals they prey on. But what happens when predators interact?

That is the question scientists are trying to answer through observation of gray wolves and mountain lions in northwestern Montana.

A just-completed study of predator interactions has opened a window onto their behavior. The study has yielded surprising results, particularly about the degree to which wolves affect mountain lions. The impacts may have ramifications for wildlife prey species and possibly for humans as well.

The study, conducted by the Hornocker Wildlife Institute, a nonprofit organization affiliated with the University of Idaho, was the first ever done of wolf and mountain-lion interactions.

It comes after the wolf, pretty much eradicated from the Lower 48 states after being a threat to livestock and perceived threat to humans, is being reintroduced by humans to habitats throughout the West. The reintroduction is mandated by the Endangered Species Act to re-establish wolf populations.

In addition to the well-publicized reintroduction in Yellowstone National Park, wolves have also been reintroduced in central Idaho and are scheduled to be released next spring in eastern Arizona. The Olympic Peninsula is among the places being considered for wolf reintroduction.

Tracking the lions

In 1993, the Hornocker Institute, known for its work conserving tigers in Siberia and with mountain lions and other predators in North America, began a study of gray wolves that migrated naturally from Canada into the United States. The wolves recolonized an area of prime mountain lion habitat along the North Fork of the Flathead River in northwestern Montana, just west of Glacier National Park.

For the study, biologists put radio collars on 40 mountain lions in order to follow their movements and used snow tracking to study the interactions between the cats and the wolves.

According to Toni Ruth, the study project leader, wolves and grizzly bears tend to harass and cause the deaths of mountain lions to a greater degree than was previously understood. When wolf packs encountered mountain lions, the cats were generally chased off or killed, she said. The recolonized wolves commonly drove lions away from their prey kills - mostly white-tailed deer or elk. The lions were then forced to make additional kills in order to survive.

"In one tracking sequence in fresh snow," Ruth said, "wolves chased a lion from a kill site, in and out of cover, and treed the lion. The wolves went back up to the kill site, and later the lion went back to the site but there was nothing left."

The study also documented that grizzly bears usurped both mountain lion and wolf kills. Some bears tracked lions to kill sites, apparently while staying out of hibernation for an entire winter. Over the course of the study, the biologists documented that wolves killed three mountain lions, a grizzly killed another one, and three more were killed by other lions.

Seven other cats died of starvation. "The starvations are probably related to mountain lions getting bumped off of their kills," Ruth said. "They're expending the energy to make a kill but are not able to reap the benefits. There is also the compounding problem of a decline in prey availability."

Female lions in wolf territory also seem to have fewer surviving kittens, Ruth added. In one case, a grizzly tracked a lion back to its den, and may have killed one of the kittens there.

Data from the study have influenced other biologists working with mountain lions or their prey species. "I think the role of this project is to take that extra step farther back and look at how a totally natural system would have been," said P. Ian Ross, a Calgary-based wildlife consultant who has studied mountain lions extensively."It's a real good classroom to observe and allow us to make some predictions."

Conflicts to come

Most wildlife biologists agree that, in recent times, mountain-lion populations have expanded significantly beyond their historic numbers across the West, in part because of the absence of wolves. In areas where wolves are re-established, lion populations will probably be reduced in size in the long run, and some prey populations will also likely be diminished, Ruth said. After reintroductions, wolves will probably displace lions from ecosystems, and in some cases drive the cats into areas of human habitation, she added.

"Mountain lions are able to cope with human areas, which wolves stay away from," she said.

Another factor that may draw lions to populated areas is that, according to earlier studies, deer tend to retreat to the edges of wolf territories. In some places, that would provide lions with an available prey species close to ranches or towns. Ruth believes that in eastern Arizona, where the Mexican wolf is to be reintroduced next spring, displaced lions may be driven to prey on cattle or pets.

"There could be impacts for local livestock owners as well as for bighorn sheep in New Mexico," a state endangered species there, Ruth said.

The Arizona plan has already been controversial with residents in the reintroduction area, particularly ranchers and Native American tribes who are concerned about the impacts of the wolves on livestock and wildlife.

Dave Parsons, leader of the U.S. Fish and Wildlife Service's Mexican wolf-recovery program, said he was familiar with the Hornocker study, and agreed that some mountain lions would be displaced when wolves are reintroduced. "When wolves were taken out, other predators made adjustments to fill that void. I expect we're going to see an unsorting of that when we go back (and reintroduce wolves)," he said.

However, he added that he expected the ecosystem to eventually reach a natural balance in which predators would kill roughly the same number of prey animals that they now do. "It will take a little time for the predatory community to go through this transition, but eventually there will be a few fewer lions and a few fewer coyotes, so that the overall predation pressure will remain relatively unchanged," Parsons said.

Wolves on the Peninsula

The U.S. Fish and Wildlife Service is waiting for an appropriation of funds to begin a feasibility study for a wolf reintroduction on the Olympic Peninsula, according to Dave Frederick, supervisor of the agency's Western Washington office. But because interactions between predators may vary greatly in different types of terrain and habitat, little is known about how the animals would behave on the peninsula.

"When you put a top-line predator in with other top-line predators like mountain lions, bears and whatever else, there is competition," Frederick said. "There's always the possibility that wolves will displace lions to a certain extent. A lot of this is site specific, and there is no baseline data for wolf-mountain lion interactions on the peninsula.

Before wolves recolonized northwestern Montana, modern biologists had little opportunity to study wolf and mountain-lion interactions. In recent times, the two predators have coexisted only in a few limited areas. (What are apparently remnant populations of wolves still reside in northern Washington in the Cascades and Selkirk Mountains, which also hold mountain lions.) However, interactions between the two predators were never studied.

The Hornocker study is one of four being done of the same group of wolves in Montana. In addition to the mountain-lion study, biologists from the University of Montana are studying wolf predation on hoofed mammals, interactions between wolves and coyotes, and genetic traits of the wolves. The researchers shared data about the wolves and other mammals.