On The Brink

On a September morning in 1981, a dog named Shep was patrolling his owners’ ranch in Meeteetse, Wyoming, when he discovered an intruder: a black-footed ferret. They scuffled, and Shep killed the animal. Although the ferret didn’t survive, Shep’s finding was good news because everyone thought black-footed ferrets were extinct. This act changed the course of the black-footed ferret’s existence.

The black-footed ferret, or BFF for short, is sleek and cute. It’s a member of the weasel family with a long body and a black face mask that makes it look like a prairie bandit—which it sort of is. It operates at night and eats mostly prairie dogs. After a BFF kills a prairie dog, the ferret steals its underground home, called a burrow. “They’re incredibly cute, but they’re also highly effective predators,” says Ryan Moehring, a spokesman for the U.S. Fish and Wildlife Service (FWS).

Black-footed ferrets are also survivors. Thousands roamed the grasslands of North America, called prairies, more than 100 years ago. Their numbers have since plummeted. In the 20th century, black-footed ferrets were twice thought to be extinct. But the BFF that Shep killed proved once again the critters were still around. 

After Shep’s discovery, researchers from the FWS scoured the area and found a colony of about 100 black-footed ferrets near the ranch. But by 1986 there were only 18 left in the wild, so the biologists scooped them up and started breeding them in captivity in an effort to save the species from extinction. 

In 2016, the FWS released 35 black-footed ferrets in Meeteetse to celebrate Shep’s discovery. Thirty years of captive breeding and releases have brought hundreds more back into the wild in their range across great Plains and Rocky Mountains (see map, above). Hundreds more remain in captivity for breeding to re-establish wild populations. But despite these successful breeding programs, the BFF remains on the endangered species list. 

Many factors have contributed to the BFF’s decline. Humans have been developing the prairie habitat the animals call home. Their main food source, prairie dogs, is also dwindling because of habitat loss, unpopularity with ranchers, and a disease called sylvatic plague.

Sylvatic plague is caused by the same bacteria responsible for the bubonic plague in humans, which killed one-third of Europe’s population in the Middle Ages.

It is just as deadly—if not more so—in prairie dogs and BFFs. Fleas carry the bacteria that cause the sylvatic plague. When fleas bite animals like prairie dogs or BFFs, they pass along the disease. It’s fatal in nearly all cases.

“That’s our job: to save species to the point where they no longer need to be listed on the endangered species list,” says Moehring. “The plague is a large hurdle.”

Because prairie dogs are key to the survival of BFFs, it’s important to help them fight the sylvatic plague. But that’s easier said than done. Although individual prairie dogs live in burrows, the burrows are connected in networks called prairie dog towns that cover very large areas. This makes reaching the wild prairie dogs difficult.

 At first, biologists at FWS used insecticide to kill the disease-carrying fleas. They would travel to prairie dog towns, and spray the insecticide into the entrances to the burrows. “It’s a very time- and cost-intensive endeavor,” says Moehring. “And it’s not very efficient.”

Now scientists from the FWS and the U.S. Geological Survey are fighting the disease with a tool used for humans: vaccination. A vaccine allows a body’s immune system to build up defenses against a specific disease. But unlike the shots you get at the doctor, this vaccine is an edible peanut-butter-flavored pellet. 

So far, the vaccine has worked well in trials. In one study, 15 of the 16 vaccinated prairie dogs survived exposure to the bacteria that cause sylvatic plague.

Now the FWS is testing methods to vaccinate wild prairie dogs. One method is to deposit the pellets near prairie dog towns using all-terrain vehicles. Another method is to deliver the pellets using unmanned drones (see "Giving Vaccines to Prairie Dogs").

“We believe we are going to be successful,” says Moehring. But he warns it’s a long road ahead. Saving a species like the BFF will require effort from not only government and conservation organizations, but also from everyone who lives in the prairie regions of the West and Midwest where the animals once thrived. Moehring says private landowners are some of the best partners the government has to help reintroduce and save the species.

 “We have all these amazing creatures here in North America in people’s backyards,” says Moehring. “Animals like the black-footed ferret are part of our American heritage; they’re part of us.” 

Use the information in the table to calculate the percent change of BFF kit births. Round all answers to the nearest percent.

Complete the chart below to determine the percent change in black-footed ferret kits born in captivity. Then indicate with a check mark whether it was a percent increase or decrease. 

A. Looking at the table of kit births, between which two consecutive years do you think the percent change was the smallest?

B. What is the percent change between those years, rounded to the nearest tenth?

A. What is the percent change of ferrets born from 1989 to 2010? 

B. What is different about this number from the answers in the percent change chart to the left?

What is the percent change in kits between the year with the most kits born and the year with the fewest? 

How can percent change help show trends in the total U.S. population of black-footed ferrets? Explain your reasoning.