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Across the Border

In November of last year, biologists with the U.S. Fish and Wildlife Service announced the release of another group of captive-bred Black-footed Ferrets near Janos, Mexico. The release brought the number of ferrets at the site to about sixty-five -- all raised in U.S. breeding facilities and then deposited more than a hundred miles south of the border.

While the announcement cheered those rooting for the ferrets' survival, it no doubt puzzled others. Why is the U.S. government trying to reestablish an endangered species in a foreign country?

Black-footed Ferrets, it turns out, prey almost exclusively on prairie dogs, and while both ferrets and prairie dogs once ranged across the Great Plains, from southern Canada through northern Mexico, alteration of the Plains ecosystem due to agriculture and the relentless persecution of prairie dogs led to the near extinction of the ferret. In fact, the species was believed to be extinct until a small colony was discovered in Wyoming in the early 1980s. When this population unexpectedly crashed after an outbreak of disease, the last eighteen wild specimens were captured to start a special breeding program.

The program was a success, and Black-footed Ferrets have been released into the wild at sites in Wyoming, South Dakota, and Nebraska. Although these populations are growing, their dependence on small isolated colonies of prairie dogs means that they're still at risk of extinction if the host colony is struck with distemper or plague. Thus reestablishing ferrets in the United States will depend upon increasing the populations of prairie dogs in the Great Plains, too. But some farmers and ranchers still regard prairie dogs as pests. Case in point: it wasn't until 1995 that the state of Nebraska repealed a law requiring landowners to exterminate prairie dogs.

Which brings us to Janos, Mexico. Currently, the prairie dog colony there is the largest contiguous disease-free colony in existence. About a half-million prairie dogs inhabit the area, and biologists hope that the population of ferrets reestablished at the site will flourish and contribute to reaching the goal of 1,500 free-living individuals by 2010. If so, the Black-footed Ferret may be saved from extinction. Still, we'll never know what other species were unknowingly eliminated when our ancestors eradicated 90 percent of the North American prairie dog population.