In 1978, the last black-footed ferret, one of six that had been "rescued" in a hapless captive breeding program, was pronounced dead, and the species, along with the recovery program, was considered extinct.

Therefore, in 1981, when a black-footed ferret scurried across a ranch in Meeteestse, Wyo., hope was rekindled and the species was reborn. The fact that Shep, the rancher's dog, had killed the ferret was an unfortunate detail, but it couldn't obscure the larger fact that ferrets were living and thriving somewhere in the neighborhood.In the years that followed, research teams monitored the population, and by 1984 they had identified 128 ferrets. They were living well and roaming freely in prairie dog burrows (their natural habitat), having first feasted on the occupants (prairie dogs being their almost exclusive prey).

Evidently the species was making an ecological comeback quite successfully, with minimal meddling from its good friend man. The reprieve was exciting but all too brief, for by the end of 1985 the population suddenly dwindled to about 24 ferrets. Just what had happened to cut short this promising return of the species?

The ferrets' undoing was apparently their diet and lifestyle. Being dependent on prairie dogs for both food and housing, the ferrets could thrive only as long as the prairie dog prospered. Unknown to the ferrets, this kind of overspecialization is a principal cause of extinction.

As if to prove that point, nature selected the winter of 1985 to deal a double whammy to the ferret with back-to-back epidemics. First it was the flea-borne plague (in humans, the bubonic plague) that decimated the ranks of the prairie dog towns and reduced the ferret population by 50 percent. As soon as the plague subsided, along came an epidemic of canine distemper that almost wiped out the remaining ferrets.

Now was the time for man to come to their rescue, so six of the remaining ferrets were taken into protective custody by the Fish and Wildlife Service. One, unfortunately, had contracted distemper and passed it on to the other five that weren't in quarantine. All six died, confirming the fact that canine distemper is often 100 percent fatal to the ferret.

Another six ferrets were collected, quarantined and vaccinated, and by March 1987 there was a total of 18, of which 11 were female, mostly of breeding age. Happily, 1988 was a baby boom year for captive ferrets, and the population grew to 55 after two breeding seasons. By the fall of 1991, with about 250 ferrets in captivity, 49 captive-bred juvenile ferrets (10 to 14 weeks old) were released into a prairie dog village in Shirley Basin, Wyo. Because the ferrets had been weaned on prairie dog meat and had already learned how to kill their prey, resident prairie dogs felt the sting of the ferrets almost immediately.

Life was not easy for the ferrets, since they had no experience in how to avoid predators. If they didn't learn immediately at the first encounter, they would not get a second chance. Biologists expected a mortality rate of 85 percent to 90 percent, and the season ended with numerous casualties from coyotes, badgers and owls; several ferrets, either injured or not adapting, were returned to captivity. Consistent with predictions, only four of the 49 ferrets made it through the winter, but they more than doubled their population with the birth and survival of six kits.

In 1992, 90 ferrets were set loose in the basin, and after the winter season about 20 were known to be alive; moreover, they had found mates and were contributing to a stable population. With a release rate of about 100 ferrets each year, by 1996 there were more black-footed ferrets back in the wild than there had been in 1984 when the recovery program began. Each generation of ferrets born wild is more able to fend for itself, and the guarantee of survival through reproductive years continues to increase.

Knowing that we will never again have 100 million acres of prairie dogs and ferrets, wildlife biologists are focusing on healthy prairie dog towns of 7,000 to 8,000 acres for each fifty ferrets. Five of these settings, located judiciously in the several states where prairie dogs flourish, would help to guarantee a permanent return. Other guarantees would be to protect prairie dog lands and to reimburse ranchers and farmers for the loss of control of a portion of their property.

A most welcome bonus to the prospering company of ferrets would be the discovery of other specimens in the wild. This is not a phantom hope, for several have been sighted by responsible witnesses in areas hospitable to the species. The contribution of a wild bunch to the limited genetic pool shared by all of the captive-bred ferrets would be their best assurance of success. There is no doubt that the species is on the rise, that the experts have learned much since the early days of ferret bungling and that badlands and prairies may again be graced by scurrying black-footed ferrets.

Phil and Nancy Seff are the authors of several science books, including "Our Fascinating Earth." Their column runs regularly in the Deseret News Science/Technology section.