- Black-footed ferrets were nearly wiped out by plague in the 1980s, and were only saved by a last-ditch effort to pull the 18 remaining individuals into a captive-breeding program.
- The wild population now numbers about 300 individuals, but the species remains reliant on captive breeding and sensitive to disease outbreaks — a combination that proved especially nerve-wracking during the COVID-19 pandemic.
- Luckily, black-footed ferret keepers are no stranger to disease-mitigating measures, and were able to successfully breed ferrets with the help of rigorous sanitation measures, dedicated staff, and even a vaccine.
- To date, no black-footed ferrets have tested positive for COVID-19, and after a 50% drop in the number of kits born last year, the program is back to producing its usual number of kits.
In spring 2020, the COVID-19 pandemic took off in the United States just as the breeding season for the black-footed ferret (Mustela nigripes) commenced. Disease is always at the forefront of the mind for the conservationists who work with this human-dependent species, but the pandemic kicked things into high gear. Suddenly, breeders at seven different centers across North America had to scramble to adapt in the face of the pandemic.
“I’m always scared,” said Pete Gober, a black-footed ferret recovery coordinator. “But when COVID came along, we were terrified.”
The bandit-masked little mustelid nearly went extinct in the 1980s thanks to diseases introduced by European settlers like plague and canine distemper. It only survived due to a last-ditch effort to round up 18 remaining individuals from the last wild population in Wyoming.
Only seven of those ferrets would survive to pass on their genes and seed a captive-breeding program that has since produced around 10,000 individuals. In any given year, there are about 300 ferrets spread across seven facilities across the United States and Canada. Of those, conservationists release about 200 young ferrets back into their native range in the Western United States each year.
Because populations in the wild still suffer from plague outbreaks, the species remains reliant on a continuous influx of ferrets from captive facilities. The wild population fluctuates, but hovers at around 300 individuals. Periodic plague outbreaks in colonies of prairie dogs (Cynomys spp.) — ferrets’ favorite food — have kept wild numbers from rising beyond that. Constant vigilance against disease is an everyday reality for anyone who works with the species.
“We had no idea what to expect with the pandemic,” said Paul Marinari, senior curator at the Smithsonian Conservation Biology Institute and keeper of the black-footed ferret studbook, which is a record of every ferret that has passed through the breeding program. “We were concerned that this disease could wreak havoc in the breeding population.”
Much like with humans, it wasn’t clear at first how dangerous COVID-19 could be to black-footed ferrets, although conservationists knew enough to be wary. Ferrets in general tend to be susceptible to respiratory diseases.
This meant captive-breeding facilities scrambled in 2020 to figure out how to safely keep the program going in the face of yet another potentially harmful disease. They managed to pull it off thanks to the help of new security measures, a tireless and dedicated staff, and a vaccine that came even quicker for ferrets than for humans.
Beefing up protections
The pandemic posed several hurdles to the captive-breeding program. First, conservationists had to supercharge sanitation measures at a time when masks and other equipment were suddenly in short supply. They also had to figure out how to provide the same level of care to the animals without the help of volunteers or any other non-essential personnel who were in lockdown.
Then there was the issue of transportation. Typically, officials move ferrets across the Canadian border and between states each year to be paired up with partners that maintain the species’ genetic diversity. (Ferrets are paired off through a program that Marinari calls “Match.com on steroids.”)
But with COVID-19 spreading rapidly, international travel was suddenly off the table, and, for a while, they didn’t even know if they’d be able to move ferrets across state lines, Marinari said.
One thing was certain: they couldn’t afford to just give up on breeding entirely.
“It would have been pretty devastating genetically to the overall population if we didn’t produce anything last year,” Marinari said.
On top of being a genetically bottlenecked species, individual ferrets are only bred for a few years, Marinari said. That means skipping a year of breeding would have been equivalent to losing a full third of the potential captive-breeding population.
Deciding the show must go on, each facility scrambled to lock down their ferret buildings, put barriers between individual enclosures, secure N95 masks and other equipment, and divide shifts to minimize caretaker contact with both ferrets and each other.
The Black-footed Ferret Conservation Center near Fort Collins, Colorado, went further still.
This single facility houses about 180 individuals — a full 60% of the black-footed ferrets in captivity — and typically acts as a staging area for ferrets bound for release. While a COVID-19 outbreak at other facilities might impact a handful of ferrets, an outbreak here could devastate a sizable chunk of the entire species. Normally, the ferrets are split between four different buildings containing 45 ferrets each. The center took the “rather drastic action” of clearing out three more buildings to separate the ferrets into smaller and more spread-out subpopulations, Gober said.
“If things went south in a particular room, we wanted to try to save as many animals as we possibly could,” he said.
Then Gober’s colleague, Tonie Rocke, a research epidemiologist at the National Wildlife Health Center, got an idea to protect the ferrets more directly: vaccination.
Vaccine for ferrets
Having worked with the black-footed ferret recovery effort for more than two decades, Rocke called Gober up in early spring 2020 and asked why they couldn’t give the ferrets a vaccine for COVID-19, too.
Heartened by studies on hamsters and mice showing that the mammals developed antibodies after injection with spike proteins — proteins on the outside of a virus that the latter uses to enter cells — Rocke bought purified versions of the coronavirus’s spike proteins. These are the same part of the virus that would eventually be used in human vaccines to teach our bodies to fight back against the novel pathogen.
“We decided very early on in the pandemic to give [vaccines] a try,” she said. “We did it out of an abundance of caution to make sure that we wouldn’t lose the species again.”
Rocke produced a vaccine using the spike proteins, then tested it on 24 captive black-footed ferrets in May 2020. When the test ferrets developed antibodies and seemed to suffer no ill effects, Gober made the call to vaccinate ferrets at the national center. They vaccinated two-thirds of them last September — months before any vaccines would be available to humans.
They left the remaining third unvaccinated because “in the ferret world, you never put all your eggs in one basket,” Rocke said.
Since then, researchers at Colorado State University have conducted a controlled study in which they exposed six post-breeding-age black-footed ferrets to COVID-19. The ferrets got infected, but they didn’t get very sick, which was “a relief,” Gober said.
“It relieved me from having to gnash my teeth and wring my hands,” he added.
Still, they’ve thankfully never had to put this result to the test in a real-world setting. The precautions have, to date, worked: there hasn’t been a single case of COVID-19 in any of the captive ferrets.
The pandemic did have some costs to the ferret conservation effort, however. Mothers bore about 50% fewer kits last years, and the kits born in Toronto are now a little more inbred since they couldn’t travel between countries. Conservationists also cancelled artificial insemination procedures to minimize human contact. But fewer kits is much better than none at all, and conservationists still released 81 ferrets into the wild last fall.
Better still, numbers are back up to normal this year. According to Gober, the program will release about 200 ferrets into the wild this fall, and one of the facilities, in Phoenix, has had its best breeding season in 20 years. The success of the black-footed ferret program has always come down to a lot of incredibly passionate and hardworking people fighting to save this species, Marinari said.
“Our plans are to continue breeding efforts full bore next year,” he said. “And hopefully we all as a globe can defeat this thing.”
Banner image of endangered black-footed ferrets by Kimberly Fraser / USFWS via Flickr (CC BY 2.0).
