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New study targets long antelope migration in western Wyoming
A small herd of antelope makes its way through the Red Hills region of the Gros Ventre drainage toward traditional summer range in Grand Teton National Park in this photo from spring 2009. The annual migration from the animals' winter range south of Pinedale has been determined to be the longest of any big game animal in the continental United States. (Mark Gocke/Star-Tribune correspondent)

CHEYENNE -- Biologists have begun the most detailed study yet of an antelope herd that makes the longest big-game migration in the lower 48 states.

Scientists recently put tracking collars on 30 antelope in the herd, a larger sample using more sophisticated devices than in any previous study. The scientists plan to spend three years studying what affects the animals' health, survival and migration.

The scientists want to find out whether wolves, fences and gas drilling might be affecting the roughly 400 antelope, also known as pronghorn.

The herd in western Wyoming spends each winter in the Upper Green River Basin and each summer in Grand Teton National Park. The antelope migrate 90 miles or more, one way, between those areas each fall and spring.

The fall migration begins in late October or early November and takes a few days, said Steve Cain, senior wildlife biologist for Grand Teton.

"It's a pretty fast and deliberate movement," Cain said. "They just decide it's time to go, and off to the wintering ground they go, post haste."

Slowed by lingering snow and stopping now and then to graze on new greenery, the antelope take about a month to migrate north in the springtime.

One goal is to fully understand the antelope and their habitat in Grand Teton, the Upper Green River Basin and in the places between, said Jon Beckmann, a biologist with the Wildlife Conservation Society.

"It's really critical that we protect all three of these components," Beckmann said. "If we don't, we could conceivably lose pronghorn from Grand Teton National Park and the Jackson Hole area in general."

Previous studies have shown that antelope avoid high-density gas development in the Upper Green River Basin, he said. For now at least, the valley seems to have sufficient winter range, and the health and numbers of antelope are stable, he said.

"What we see in this case and in a lot of cases globally, is that national parks are too small to protect ecological phenomena such as migrations," Beckmann said. "This is a good example of something that is happening outside a park boundary that influences a species that uses a national park."

One question the study could look into is whether wolves might be helping antelope numbers in Grand Teton, Cain said.

Past research has shown that coyotes prey on antelope fawns. "The idea is that the presence of wolves would decrease the numbers of coyotes, which would increase pronghorn fawn survival," Cain said.

Another question is whether efforts to make fences friendlier to antelope are paying off. Antelope prefer to crawl under fences rather than jump over them.

Groups have been working with landowners to install fences that don't impede antelope near the ground, Cain said.

Biologists also hope to figure out why some antelope don't migrate all the way to the Upper Green River Basin. Usually antelope that don't complete the migration also do not survive the winter.

Last winter, an unusually large group of 40 antelope stayed in Jackson Hole. They migrated southward in mid-February but didn't go all the way to the Upper Green River Basin, said Doug Brimeyer, a Game and Fish biologist based in Jackson.

Most found enough forage to survive.

"It was a fairly mild winter," Brimeyer said. "If we tend to have more wild winters with the current climate that we're seeing, there's the potential for that to occur a little more often."

Two antelope that were collared for the study already have died. The causes of their deaths were not immediately known.

The study is a jointly funded collaboration among Grand Teton, the Wyoming Game and Fish Department and the Wildlife Conservation Society.

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