Prairie dogs beware: the ferrets are back.

As of five years ago, predators and back-to-back epidemics had all but extinguished the black-footed ferret With the help of state and federal scientists, however the species is weaseling its way out of extinction. Biologists rounded up the last surviving community of these ferrets in 1986 to launch a captive-breeding program (SN: 9/6/86, p. 151). Those 18 wild animals provided the 49 juveniles that researchers have just finished releasing into a prairie dog village in Shirley Basin, Wyo.

Resident prairie dogs are already feeling the sting. Weaned on prairie dog meat, the newly released, 10- to 14-week-old ferrets know how to kill prairie dogs," says Stephen C Torbit of the US Fish and Wildlife Service in Cheyenne, Wyo. Besides serving as the main source of ferret food, prairie dogs dig the burrows these masked squatters call home.

But the newcomers don't have it easy. Since the ferrets began arriving in September coyotes and a badger have killed five. Such casualties were bound to occur among animals lacking experience with predator avoidance, Torbit notes. "We had talked about mortality rates after a year - or by next spring - of 85 to 90 percent," he says. Two other ferrets - one with an eye infection, the other injured in a fight with a prairie dog - are temporarily back in captivity for nursing.

Some 260 black-footed ferrets remain in captivity. If the breeding program goes as planned, says Torbit, another 100 youngsters should be available for release next fall.