When wolves were reintroduced in Yellowstone National Park in 1995, no one was anticipating that their arrival would improve tree growth. But it did. No one expected that more wolves would mean more pronghorn antelope either. But it turns out that thanks to wolf reintroduction, more pronghorn fawns began surviving.

How Did Wolves Do All This?

Yellowstone National Park had an elk problem in 1995 when the wolves arrived on the scene. There were too many of them, and the park was beginning to suffer from overgrazing. Cottonwoods, willows,aspen and other woody species were disappearing thanks to about 15,000 elk chowing down on them. The problems was especially problematic along streams and rivers, causing water temperatures to rise and beaver and riparian songbirds to disappear along with the trees and brush they relied on for survival.

The wolves did two things. First, they ate some elk and slowly the population began to decline to a level the park could support. They also changed the behavior of the remaining elk who had to spend time watching out for predators, giving them less time to graze off tasty aspen shoots.

As a result, trees and shrubs began recovering along streams. Habitat improved for beaver and fish. Bears had more food, and hundreds of species of birds, mammals, fish and reptiles began to return to their niche in Yellowstone’s ecosystem. By 2006, some aspen trees had grown tall enough they were no longer susceptible to browsing by elk. Cottonwood and willow were also beginning to return in places so that songbirds, like the common yellowthroat, warbling vireo and song sparrow could once again be found in the Park. And thanks to the work of beavers building dams, waterfowl found new homes too.

Wolves also changed coyote populations and behavior. Some coyotes were killed by wolves and others shifted to safer areas without wolves. Fewer coyotes meant increases in populations of small mammals, a good thing for the red foxes, ravens and bald eagles that rely on them for food and pronghorn antelope numbers went up too.

While we might have expected wolves to eat the fawns, that isn’t what seems to happen. According to researcher Dr. Kim Berger, “wolves are so much bigger than coyotes that it doesn’t make sense for them to waste time searching for pronghorn fawns. It would be like trying to feed an entire family on a single Big Mac.” Researchers found that where coyotes had been dense, only 10% of fawns survived. But where wolves were present, survival rates went up to 34% and the Yellowstone herd has doubled from a low of 200 in 1995 to about 450 today.

What we’ve learned is that the relationship between predators and prey can be very complex and our efforts to manipulate ecosystems can have unexpected consequences. While wolves may not be a welcome sight for many ranching operations in the west, perhaps understanding their behavior and their place in the ecosystem will help us come up with better ways to protect stock. If you’ve found something that is particularly helpful, please share it with your fellow On Pasture readers below.

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