Building tolerance for a little grazer is key to the survival of black-footed ferrets
By Chamois Andersen
A harvest moon hangs over the prairie as a coyote calls to his pack in the distance. “I wonder if it caught a pronghorn,” I say to Dana Nelson, a Wyoming state wildlife biologist. We’ve been seeing pronghorn eyes shine in our spotlight all night on the grasslands of Shirley Basin where, as a field representative for Defenders of Wildlife, I am helping with the state’s annual survey of the endangered black-footed ferret population.
“I spot one,” I whisper. “See the eyes?” I hold my binoculars steady, slowly scanning where it goes. The long-bodied animal darts in and out of the prairie dog burrow, where it lives. I swivel the handle on my high-powered spotlight attached to the truck window. The light shines about 600 yards, where I pick up another pair of emerald eyes. “We’ve got two over there on the rise,” says Nelson. “I wonder if they’re siblings. It looks like they’re playing tag.”
Black-footed ferrets appear to be doing fairly well in Shirley Basin. This is mostly because the prairie dog population, which ferrets need to survive, is robust, with colonies covering tens of thousands of acres. It is one of 30 sites in 11 U.S. states, one Mexican state and one Canadian province where the ferrets have been reintroduced.
The backdrop to this recovery story is the Great Plains—400 million acres stretching from Canada to Mexico that once had an abundance of wildlife unmatched anywhere else in North America, with wolves, elk, bison, prairie dogs, black-footed ferrets, grassland birds, swift foxes, pronghorn and more.
Today much of this vast region is fenced for cattle grazing, covered in crops or developed for uses that include energy and mineral extraction. Yet it still holds incredible beauty and biodiversity in a place where prairie grasses roll on for miles before meeting a giant canvas of blue sky at the horizon, and animals depend on the land and each other for survival.
As a conservationist working in the field for more than two decades in a variety of environments from mountains to marine ecosystems, nowhere have I observed the interdependence between wildlife and the land like on the plains.
This synergy is the reason Defenders has spent decades attempting to protect and restore black-footed ferrets and prairie dogs to their historical habitat.
That the black-footed ferret survives at all is no small miracle. Thought extinct in the 1970s—after once numbering in the tens of thousands—this sleek, cream-colored creature smaller than a housecat is the only ferret native to North America.
When a rancher’s dog in Meeteetse, Wyoming, deposited one on his owner’s doorstep in 1981, the U.S. Fish and Wildlife Service went looking and discovered a remnant population, enough to launch a captive-breeding program in hopes of saving the species.
It’s been a recovery fraught with setbacks. Today—with some 4,500 captive-bred black-footed ferrets released in prairie dog colonies across North America since 1991—the total ferret population still only stands at about 350, most at only a few sites, including Shirley Basin.
Scientists estimate that it takes at least 120 breeding adult ferrets to maintain a healthy, viable population in the wild. And each population requires well more than 10,000 acres of prairie dog colonies—at a time when prairie dogs occupy less than 5 percent of their original habitat. Prairie dogs also make up 95 percent of a ferret’s diet, about 100 to 150 prairie dogs a year per ferret. And ferrets fully depend on prairie dog burrows for shelter.
As a key ecosystem engineer, prairie dogs are important to the survival of an abundance of grassland species. They clip tall grasses and shrubs in their colonies, creating islands of short vegetation in a sea of taller grass that attract birds such as the mountain plover, which nests on flat, bare ground. The shorter vegetation is often more nutritious and preferred by grazing wildlife such as pronghorn and bison, as well as cattle. As prairie dogs dig and burrow, they mix minerals in the soil, and their homes provide habitat, shelter and nesting areas for other creatures, including swift foxes, burrowing owls and many amphibians and reptiles.
Unfortunately, few prairie dog complexes remain.
“Most people know about the massive bison slaughter in the 1800s, but fewer know about the prairie dog eradication of the 1900s that continues today,” says Jonathan Proctor, Defenders’ Rockies and plains program director. “This loss of more than 95 percent of prairie dogs is why Defenders focuses on restoring and protecting large prairie dog colonies, working with willing landowners, including Native American tribes and land trusts, and on public lands that belong to all of us.”
Proctor points to the Haverfield ranch in western Kansas as a prime example of a ranch family protecting a priority ferret site and taking a leading role in imperiled prairie wildlife restoration.
“This ranch teems with wildlife while also profitably grazing cattle,” says Proctor. “It quite possibly is the most wildlife-abundant spot in western Kansas because of its large prairie dog colonies, which provide food and homes for the reintroduced ferrets as well as the swift fox, burrowing owls, ferruginous hawks, golden eagles and a host of other species.”
Defenders became involved with the Haverfields in 2007 when the family began fighting a 1901 Kansas law requiring landowners to eradicate prairie dogs and volunteered their ranch as a ferret recovery site. “Their refusal to remove prairie dogs on their private property and their excitement to help restore an endangered species brought the lifelong-ranching family significant national media attention, and they used it to show the world that ranching and wildlife can go hand in hand,” says Proctor.
Two other priority recovery sites for Defenders are Conata Basin, located on parts of Buffalo Gap National Grassland and Badlands National Park, and the Lower Brule Indian Reservation in South Dakota. To protect these areas, Defenders has thwarted poisoning campaigns, worked to reduce conflicts with ranchers and collaborated with the Prairie Dog Coalition to hand-dig starter burrows and relocate prairie dog colonies from plots slated for poisoning.
At Lower Brule, a new site with 200 prairie dogs connects to dozens of acres of healthy colonies. At Conata, prairie dog colonies now span almost 10,000 acres with more than 100 ferrets—the largest ferret population in the wild.
“A good measurement of success is when a wild ferret population is healthy enough that we can use it to help establish populations at other recovery sites,” says Travis Livieri, executive director of Prairie Wildlife Research, a Defenders partner. Conata Basin ferrets have already been relocated to help populate sites in Colorado, Kansas, Montana, New Mexico, Utah and Wyoming.
But recovering ferrets at these and other sites is not without additional challenges, particularly sylvatic plague carried by fleas and introduced from Eurasia by stowaway rodents on ships in the early 1900s. Outbreaks among ferrets and prairie dogs spread with lethal speed. “Because plague kills both prairie dogs and ferrets, it can turn a once successful reintroduction site into a devastating loss in record time,” says Proctor.
Currently, the only tenable solutions to prevent plague is to methodically dust each individual prairie dog burrow with flea powder and to capture and vaccinate ferrets every year. The National Wildlife Health Center is also undertaking field trials for a new oral bait vaccine for prairie dogs.
The good news is that sites can recover after a plague event.
Hit with the disease in the 1990s, the ferret and prairie dog populations crashed at Shirley Basin, where we are now counting ferrets and have just trapped one for a health assessment.
As state wildlife biologist Dana Nelson moves her scanner back and forth above a young female ferret’s neck, Nelson notes that she is not microchipped. It’s exciting news because it means she is wild-born. In total, the state confirmed seven new litters were born successfully in the wild this field season, giving us continued reason for hope that, if we are vigilant and steadfast in our efforts, the species will recover.
With this ferret’s checkup complete, we get ready to release her back to her burrow. I open the kennel door and just before disappearing into her burrow, she stops for the briefest of seconds to look at us.
“You’re back home,” I whisper.