Rallying to Protect U.S. Antelope Migration Route

Sharon Guynup
National Geographic Today
March 28, 2003
Each spring and fall, hundreds of tan-and white-pronghorn antelope participate in one of nature's most spectacular choreographed rituals: their seasonal migration between high mountain summer range and lowland winter range.

This doesn't take place in Africa's Serengeti—it happens in the American West, in western Wyoming—and it is the longest migration of any land mammal in the lower 48 states. The antelope pass through what conservationists call "one of the most intact mountain environments on Earth," home to an abundance of bison, grizzly bears, cougar, elk, red fox, lynx and many more species.

But biologist's surveys over the last decade have found that this particular antelope population has plummeted from between 400-500 animals in 1991 to about 158 last year.

Civilization is crowding in on this herd and threatening their very survival. Development and other human activity has narrowed the animal's migration route down to a couple of hundred yards in some areas.

Saving this migration poses a set of complex challenges to conservationists and officials in national parks and wildlife agencies. "There is a need for a designated migration corridor to help ensure the survival of this population of pronghorn," says Bill Weber, director of the North American program for the Wildlife Conservation Society (WCS) in New York City.

Unique Antelopes

"Archaeological records show that their migration has gone on for at least 6,000 years," he said. The antelope migrate up to 200 miles, summering in Grand Teton National Park and wintering in the Red Desert.

Pronghorns are the only American antelope species, and are the sole surviving member of its ancient family. They have slender, graceful deer-like bodies, standing three and a half feet high at the shoulder.

They have three unique characteristics: they are the fastest animal in the Western hemisphere, running at speeds up to 60 m.p.h. They are the only animal in the world with branched horns—males sport distinctive 12-inch pronged horns that give the species its name—and they are the only creature to shed those horns seasonally, like antlers.

Once, the antelope were as plentiful as bison throughout the West; today they number a few hundred thousand, from Montana to Arizona.

Endangered Migration

The species itself is not endangered. But this particular Wyoming herd is at risk, along with its migration, posing a particularly difficult conservation challenge.

"This raises an important question for the National Park Service: Is it okay for a species to go extinct in a national park?" Weber asks.

National Parks aren't designated to protect wildlife, but today they've become reservoirs of biodiversity," said Kim Berger, an Idaho-based biologist with WCS who is studying the pronghorn and their predators. "Part of what we hope to do in the parks is preserve intact ecosystems. Loss of the pronghorn would compromise that ecosystem."

Protecting Corridors

To protect the pronghorn, biologists must preserve their migration routes. The animals summer high in the mountains within the national park. But once fall comes, they must move to lower elevation areas that receive less snow in order to survive. Those that are trapped in the park over the winter usually perish.

These animals are movers," said Franz Camenzind, executive director if the Jackson Hole Conservation Alliance. Their survival strategy is to outrun predators—which they can't do in deep snow."

"If they lose that migration route, they will go extinct," said Steven Cain, acting chief of science and resource management for Grand Teton National Park. "There's a high premium on protecting that route."

Over the last few years, biologists have identified problem areas. New subdivision development, more roadways, and booming oil and gas development are either blocking the historic migration route or creating bottlenecks.

Fences pose a huge problem for the antelope—they will crawl under, but few will leap them. In some places, pronghorns must walk down the street through newly-built residential areas south of Bridger-Teton National Forest. "We're changing their habitat faster than (the pronghorn) can change," Camenzind says.

Coyotes and Wolves

To track the fate of young antelope, Berger and her biologist husband, Joel Berger, radio collared 38 fawns last summer. "We had about 85 percent mortality," said Berger. When they recovered the carcasses, they found that most were killed by coyotes.

The coyote predation may come partly from an ecological domino effect that scientists call the "mesapredator release hypothesis."

By the 1930's, Berger explains, the area's top predator, the gray wolf, was gone from the region. That allowed the coyote to move in and take over their niche. Wolves tend to eat larger prey, like elk—but coyotes prey on young antelope.

In a celebrated program, wolves were reintroduced to Yellowstone in 1995. They are now recolonizing Grand Teton National Park.

Will they push coyotes back and ease pressure on pronghorns?" questions Weber. For the next two years, the Bergers will try to answer that question by studying wolves and coyotes—and how their ecological reorganization affects the pronghorn.

Preserving an Ecosystem

Other factors may also be speeding the pronghorns decline, including disease as well as changes in habitat and climate.

The scientists want to develop a management plan that keeps the pronghorn migration corridor open—which will require cooperation of federal, state and local agencies and private landowners.

Besides preserving this unique migratory event—one of only 29 such migrations which are imperiled worldwide—Berger hopes her research will help protect the web of life that thrives in that corner of Wyoming.

"This is one of the last intact temperate ecosystems," said Berger. "There are very few places left where you have a full assemblage of mammals. We want it to survive."

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