Plague wipes out prairie dogs, ferrets at Montana's UL Bend

One surviving black-footed ferret was counted at Montana's UL Bend National Wildlife Refuge this spring after plague killed off 70 percent of the population of black-tailed prairie dogs, which the ferrets need to survive.

Randy Matchett, a wildlife biologist for the U.S. Fish and Wildlife Service, said the large sylvatic plague event occurred over the winter of 2017-18.

Ferrets, which have distinctive black masks, consume about 130 prairie dogs a year, ambushing them in burrows at night.

They also live in unoccupied prairie dog tunnels and need large colonies to survive.

The same plague that caused pandemics in human populations in the Middle Ages, known as "black death," is lethal to ferrets and prairie dogs. It is transmitted via flea bites.

In the fall of 2017, a minimum of 24 black-footed ferrets were counted at UL Bend, Matchett said.

In the fall of 2018, the number had dropped to four.

"This spring I could find one," Matchett said. "And 70 percent of the prairie dogs have died off."

All of the ferrets at UL Bend were born in the wild but originated from ferrets that were raised in captivity and previously released as part of efforts across the West to save the black-footed ferret, an endangered species.

At this time, there are no plans to release additional ferrets at UL Bend because there is not enough prairie dogs to sustain them, Matchett said.

It will be at least a decade before the prairie dogs rebound, Matchett said.

Researchers had worked on a vaccine to control the plague at prairie dog colonies. The vaccine is contained in small cubes of bait with peanut butter that the prairie dogs eat. The vaccine was distributed at dog towns in seven states including the UL bend location.

"The vaccine did not prevent this big die-off which is what we wanted it to do but it didn't do," Matchett said. 

The effectiveness of the vaccine still is being evaluated at other locations, Matchett said.

It hasn't worked in some places where it has been applied, while prairie dogs are doing OK at others, but it may be that the plague just hasn't reached those spots, Matchett said.

"We're still very much in the evaluation stages, Matchett said. 

The severe winter of 2017-18 also could have contributed to the die-off at UL Bend, said Matchett, noting that there was continuous snow cover at UL Bend from Dec. 20 until April 15.

Once thought to be extinct, a remnant population of black-footed ferrets was discovered in the 1980s near Meeteetse, Wyoming.

Upon that discovery, the U.S. Fish and Wildlife Service and the Wyoming Game and Fish Department founded a successful captive breeding program from those animals, which continues today.

Ferrets have been reintroduced into the wild at 24 sites across the West, with the biggest challenge to recovery, besides the plague, being a lack of suitable reintroduction sites large enough to support expansive prairie dog colonies where black-footed ferrets can thrive. 

Recovery efforts have helped restore the black-footed ferret population to to estimated 300 animals across North America, according to the U.S. Fish and Wildlife Service.