Plague vaccine vital to ferret recovery in wild
Limited habitat and deadly plague infecting endangered black-footed ferrets and their prey have hobbled recovery in the wild despite a 25-year federal captive-breeding rescue run from Colorado.
The apparent survival rates of ferrets set loose on prairie have dipped below 50 percent in some areas, according to U.S. Fish and Wildlife Service data. Federal biologists say that after reintroducing 4,700 ferrets since 1991 at 28 sites nationwide, the primary problem of plague has limited the surviving population to between 400 and 500 animals.
Each of the ferrets bred and conditioned at the National Black-footed Ferret Conservation Center northeast of Fort Collins, at a cost of $5,500 each, is vaccinated and implanted with a tracking chip so that field crews can monitor meticulously in the fight to save ferrets from extinction.
The latest innovation: a blue, marble-sized pellet flavored with peanut butter to vaccinate
prairie dogs against plague. Studies have shown prairie dogs are drawn to the color blue. Ferrets eat up to 100 prairie dogs a year.
If plague in both prairie dogs and wild-born ferrets can be beaten, federal biologists contend, blackfooted ferrets are capable of reproducing rapidly.
“Managing plague is crucial. It is the key to recovering black-footed ferrets,” said Fish and Wildlife Service biologist John Hughes.
Preventing extinction also depends on healthy prairie. Hughes said it will take 500,000 acres nationwide to support a stable, self-sustaining population of ferrets. The feds still must line up 250,000 acres of public and private land for releasing ferrets to meet that habitat goal, Hughes said. “We feel that recovery would be within our reach.”
The push to save ferrets stands out because they’ve been listed as endangered since 1967 and were all but written off as extinct, a loss that would reverberate because ferrets are key predators of prairie dogs, essential to maintaining ecological balance on delicate short-grass prairie.
There are hopeful signs. Last week at the Rocky Mountain Arsenal National Wildlife Refuge north of Denver, nighttime surveys found 27 ferrets — evidence that a population estimated at 50 is enduring. Survey crews also found four kits.
“While this is an encouraging start, we won’t have conclusive data until after the surveys are complete — end of next week,” said Fish and Wildlife spokesman Ryan Moehring.
The federal government has raised 8,000 ferrets in captivity, mostly at the ferret center in Colorado. Each captive-bred ferret is prepared for a jump to the wild. Newborns are fed prairie dog meat. They move to pens where black tubes simulate prairie dog burrows and practice hunting little prairie dogs. At 4 months old, most ferrets race reflexively after big prairie dogs. Those who don’t, about 10 percent, are relegated to being display animals in a ferret exhibit at the Fort Collins Museum of Discovery.
Ferrets’ experience at the Rocky Mountain Arsenal refuge, where wildlife managers have controlled plague successfully, demonstrates the challenge. In 2015, federal wildlife biologists introduced 28 young ferrets at the refuge. The next year, surveyors found 20 of them — and posted an exceptionally high apparent survival rate of 71 percent. In 2016, the biologists introduced 16 more ferrets. Only five could be found the next year. The apparent survival rate had plummeted to 31 percent — likely because there wasn’t enough land per ferret and the new ones had to disperse, refuge officials said. An owl killed one ferret this year, and two were killed by whizzing vehicles outside the refuge.
Predators are considered crucial for broader efforts to revive the nation’s ailing prairie ecosystems that have been hammered by industrial agriculture and fragmented by roads. Ferrets evolved on prairies. Their wiry elongated bodies and super-sensitive snouts let them slink at night through underground tunnels into prairie dog dens. Ferrets clamp their teeth into sleeping prairie dogs and swiftly devour them.
For thousands of years, ferrets hunted across grasslands in Colorado and at least 11 other states. Poisoning and hunting rendered them scarce by the 1930s and nearly extinct by the 1980s. Rancher John Hogg found a small population on his land near Meeteetse, Wyo., in 1981. Federal biologists plucked away 18 of those last survivors and bred them at the center northeast of Fort Collins, aiming for genetic diversity, and at five other sites including the Cheyenne Mountain Zoo in Colorado Springs.
They have been releasing ferrets in the wild since 1991, starting in Wyoming. In Colorado, federal crews have put out 150 since 2001 at sites including private land, under special agreements protecting landowners from Endangered Species Act liability if ferrets die. The public sites include the refuge and Fort Collins’ Soapstone Prairie Natural Area and adjacent Meadow Springs Ranch open space.
Since 2012, 80 ferrets were released in the Fort Collins natural areas, said Daylan Figgs, the city’s natural areas land and water manager.
“We are seeing some survival in wild-born kits,” Figgs said. But overall the ferret population has dropped to between 10 and 20.
“Anytime you bring an animal out of captivity and put them back in the wild, mortality rates are determined by their ability to hunt and catch food,” he said. “Sometimes prairie dogs are able to injure and kill ferrets, and there is some mortality just in ferrets’ ability to kill enough prairie dogs to survive.”