Killing Wolves Kills Other Animals Too

Scientists who have been studying the effects of restoring the wolf population in areas like Yellowstone National Park have found a surprising twist in this often emotional story.

While the return of these fierce hunters has been tough on their prey, it apparently has made it possible for many other creatures to survive and flourish because of changing eating habits of large herbivores, including elk. Now that the wolves are back, elk are less likely to feed in areas where they might be at risk, and that has facilitated the natural recovery of riverbanks and other areas that are so critical to beavers, birds, insects and other animals.

So while many researchers have been focusing on the lethal impact of the restoration of wolves, the fear of wolves by some animals has possibly had an even more dramatic impact on the entire region.

Scientists are calling it the "ecology of fear."

"The fear instilled in the elk, based on the return of wolves, has affected the ecosystem in ways we didn't think about before," says William Ripple, a forestry scientist at Oregon State University in Corvallis. Ripple and an Oregon State colleague, Robert Beschta, reported some surprising findings recently in the journals BioScience and Forest Ecology and Management.

Thinking Like an Elk

Wolves once roamed the entire North American continent, from the Arctic to Mexico, but they were nearly wiped out early in the last century because of the fear of a different animal, humans. Ranchers and hunters were particularly angry over wolves because they were blamed for killing livestock and game animals, and that attitude has not changed much.

What has changed, however, is federal protection for wolves, and an ongoing effort to re-establish wolf packs in Yellowstone, as well as several other areas. That has lead to bitter resentment by some who still fear the impact of the repatriation of wolves.

It has also resulted in wide-ranging studies of what happens when a predator is restored, and how that impacts other animals, not just the ones the predator likes to eat.

Ripple and Beschta have been studying the wolves in the Yellowstone area for several years now, and they have documented changes in the landscape that they think resulted from changes in the eating habits of the wolf's primary prey, elk.

"A couple of years ago, I was looking around in Yellowstone at patches of willow," Ripple says. "In some places the willow were growing tall, and in other places they were not growing at all. They were being browsed by the elk."

But why some places and not others?

"I kept walking out in the field, day after day, trying to understand what was going on. It was quite a mystery."

Many scientists would probably have returned to their labs at that point and worked up computer models to try and figure out why the elk had become finicky eaters, but Ripple had a better idea.

He spent a lot of time in the field, trying to "think like an elk," as he puts it.

Finally, in what he calls an "aha" moment, the answer came to him.

The areas where the elk had ceased to dine tended to be in gullies or along riverbanks or near a steep cliff. That would be a tough area to escape from a pack of wolves, and the elk apparently had figured out that they needed to stay in areas where they could see the wolves long before they became a threat, and then retreat to safer ground if it became necessary.

And the result of that was fairly dramatic.

The researchers found that areas abandoned by elk were filled with new growth, not just of willows and aspen that elk normally feed on, but bushes and grasses and smaller plants that protect stream banks.

"Once browsing decreases, the plants are free to grow, and a number of different ecosystem functions can be restored," Ripple says.

Make Way for Beavers

Beavers, which had become rare in some areas, moved back en mass. Their dams created new ponds and flooded wetlands that had been dry for decades, paving the way for the return of many other species, even insects and migratory birds.

It was, Ripple says, an amazing thing to see. And totally unanticipated.

The return of a feared predator had lead to the restoration of various habitats, thus becoming a critical ally in the effort to maintain bio-diversity.

It's an interesting footnote to a tragic era. Wolves weren't the only targets in the early 1900s.

In the Yellowstone area alone, 121 mountain lions were known to have been killed from 1904 through 1925, and 4,350 coyotes were exterminated from 1907 through 1935. And 136 wolves were killed from 1914 through 1926, by which time they were completely wiped out.

But Canis lupus is back.

The U.S. Fish and Wildlife Service and the National Park Service began restoring gray wolves to Yellowstone and other areas in 1995. Fourteen wolves were brought in from Canada, held in temporary pens for 10 weeks as they acclimated, and then released into Yellowstone.

Others were brought in later, and they rapidly reproduced. By the end of last year, there were at least 174 wolves in the region, a total of 13 or 14 packs.

Of course, a lot of elk died along the way, and nearby ranchers still blame stray wolves for the loss of some livestock, so the program is still hotly debated.

But what is emerging quite clearly is we really don't know what kind of impact we're likely to get when we just get out of nature's way. One thing seems clear. The natural balance in Yellowstone is returning.

Just ask the beavers. And the birds. And a bunch of other critters that have returned to their ancestral homes.

Lee Dye's column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.

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