Ferrets Slinking Back From Brink of Extinction in U.S.

Maryann Mott
for National Geographic News

August 9, 2007

The black-footed ferret, North America's most endangered mammal, has made a remarkable recovery from the brink of extinction, according to a new study.

A key population of the sleek-bodied predator in Shirley Basin, Wyoming, grew from a low of five in 1997 to more than 220 in 2006, the research found.

The increase marks a rapid rise from a decade ago, when disease nearly decimated the ferrets in Shirley Basin, Wyoming's only recovery site for the animal.

Scientists measured the population by scouring thousands of acres at night using high-powered spotlights.

"We only were able to survey about 14 percent of the total [150,000-acre/60,700-hectare] habitat, so there's a chance that even more ferrets are out there than we documented," said Martin Grenier, a biologist for the Wyoming Game and Fish Department who led the study.

The researchers believe more than 400 ferrets may exist.

If their suspicions are correct, Shirley Basin would be home to the largest ferret colony in the United States, a distinction previously held by South Dakota's Conata Basin (see map of the United States).

The findings are published in tomorrow's issue of the journal Science.

Thanks to Prairie Dogs?

Steven Buskirk, a zoology professor at the University of Wyoming and co-author of the study, said ferret populations generally aren't considered capable of growing so quickly.

He attributes the boom to the area's enormous prairie dog colony. Ferrets dine almost exclusively on the rodents and live in their prey's burrows.

Wyoming is home to white-tailed prairie dogs, a species less persecuted by ranchers than the black-tailed prairie dog found at other ferret recovery sites.

Black-tailed prairie dogs tend to live in highly sought after agricultural and ranching areas, where landowners often blame them for damaging crops and grazing land.

Consequently, conflicts arise and large-scale eradication programs have often ensued.

(Related: "Prairie Dogs Poisoned by U.S. in South Dakota" [October 26, 2004].)

Last month environmental groups petitioned the U.S. government to place the black-tailed prairie dog on the Endangered Species List.

A previous attempt in 1998 failed.

Alan Pollom of The Nature Conservancy's Kansas City field office is encouraged by the findings of the Shirley Basin ferret study.

But, he added, prairie dog colonies must be allowed to remain if ferrets are to survive.

"If you're going to have a lot more ferrets, you need a lot more prairie dogs," Pollom said. "There seems to be no way to get around that equation."

Welcome Back

Experts believe about 700 black-footed ferrets live in the wild.

Of the 13 ferret reintroduction sites, located in six Western states, only three have white-tailed prairie dog colonies. (In addition to Wyoming, the other colonies are in Colorado and Utah.)

In Shirley Basin, Buskirk said, conflict with ranchers is much lower than elsewhere because there's no crop production.

The ferret reintroduction project there has been embraced by private landowners, many of whom are willing to have the small mammals introduced on their property, he said.

"It's really changed from 15 years ago," Buskirk said.

"Fifteen years ago it was just a deal-breaker. Now a lot of ranchers are saying: Go ahead put them out there. Just don't cause a lot of fuss with research or monitoring activities."

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