While most Coloradans won’t be eligible for the COVID-19 vaccine until this spring or summer, some native mammal species have already received their shots.

Black-footed ferrets are one of the most endangered mammals in North America, with about 250 living in the wild, and another 250 in captivity throughout Colorado, North Dakota, and Wyoming, including the Cheyenne Mountain Zoo in Colorado Springs and the Rocky Mountain Arsenal outside of Denver.

Disease has threatened this species before. The plague, for instance, is a well-known risk for ferrets, as it tends to infect the animal’s primary food source: prairie dogs. Black-footed ferrets are also closely related to mink, a species that made headlines late last year when Denmark culled the country’s entire farmed population—about 17 million in total—after outbreaks of the novel coronavirus occurred at 200 farms throughout the country.

While scientists have yet to unravel when and how COVID-19 jumps between species, in Denmark, the virus was confirmed to have spread from humans to mink, where it mutated and was then passed back to humans—a dangerous development in the midst of a pandemic. Because of concerns that the endangered black-footed ferret could also become infected with COVID-19, scientists in the U.S. recently developed and administered a vaccine to the majority of the species’ captive population.

But that’s not the full story of these unique animals. We spoke with two ferret experts (yes, really)—Dean Biggins, a longtime black-footed ferret researcher with the U.S. Geological Survey, who has earned the nickname “the godfather of ferrets,” and Tonie Rocke, a research scientist at the National Wildlife Health Center who developed the ferrets’ vaccine—to uncover the ecological history of the threatened mammals.

5280: What are some characteristics of black-footed ferrets? What are their lives like? 

Dean Biggins: They are similar in size to the domestic ferret you buy in a pet store. Females weigh about a pound-and-a-half and males a couple pounds. [They’re] in the weasel family, but it is our native North American species. There are two other species of ferrets worldwide, one being the European polecat. The Asian counterpart is the Siberian polecat.

They’re mainly nocturnal and spend a lot of time underground. Probably 85 to 90 percent of their time is spent in prairie dog burrows. That’s what they like and where they breed. They eat prairie dogs primarily.

Ferrets, they really strongly prefer having multi-entrance tunnel systems. We presume (and we have data to support this) that’s because of badger predation. American badgers can dig down. Badgers do follow around ferrets in the wild. If they catch a ferret in a single-entrance burrow they can kill it easily.

Black-footed ferrets were thought to be extinct at one point but were then discovered in the wild. What is the story there? 

DB: By 1979, the last ferret in captivity at a wildlife research center in Maryland died. They did not find any in the wild, so they declared extinction likely but not known. Then, in 1981 ferrets were discovered in Wyoming—that occured by a ranch dog actually killing one. The rancher took it down to the taxidermist, who told him, “You just found the most endangered animal in the United States.” Word got over to U.S. Fish and Wildlife (USFW), and we did indeed find them in the wild. Total count by 1984 was around 120.

Due to disease in the colony, by winter of 1985 there were only 10 known ferrets left in captivity, and only four left in the wild. They were left out there over winter. Pretty bleak. Of the four left out there, two adult females managed to breed. They found one adult male nearby. He probably bred both of them. His name was Scarface, by the way, and is pretty well-known.

By that time, things were looking so dire that USFW and other agencies decided to just put all our eggs in the captive breeding basket and catch every [ferret] that was left out there. That’s what we did. We brought the remaining animals—the two litters and their moms and Scarface and one other male. That constituted the 18 animals total that wound up in the captive breeding program.

They’re now maintaining upwards of 250 in captivity, and we probably have something like that in the wild. We’re maintaining as many animals as we can.

And now a number of these ferrets are vaccinated against COVID-19. Can you tell us how that came to pass? 

Tonie Rocke: The black-footed ferret is probably our most endangered mammal in North America, so right from the beginning we were concerned about that population. Lab tests showed domestic ferrets were susceptible [to COVID-19]. And, of course, so are mink. All three of those [animals] are related. Black-footed ferrets tend to be more susceptible than domestic ferrets, and in captivity they have human caretakers. There was a risk of humans transmitting it to the ferrets and back again. To date, there has been no exposure in the colony, but we aren’t going to take that risk because there are so few of them.

We didn’t develop a new vaccine; we took a SARS-CoV-2 purified protein. We had used similar protein vaccines in ferrets before. We knew how to administer those. We did a small trial on a small number of animals. It boosted their immune response, perfectly safe. We saw no adverse effects, so a decision was made to vaccinate not all but two-thirds in the captive colony, just as a precaution.

What larger themes are you thinking about in terms of black-footed ferrets’ current predicament and humankind’s predicament with COVID-19? 

TR: We still don’t know a lot about COVID-19 in wildlife other than in some captive populations in zoos. There have been infections in some of the big cats at zoos, and now recently a gorilla. So, it’s mostly been captive animals we’re worried about. I think there is some concern about wild or free-ranging mink that might be close to the farms or other places where they might pick up the virus. People are starting to think about surveying wild mink but studies haven’t been done in wildlife yet.

DB: One thing that’s been on my mind is how we as humans seem pretty unconcerned when rodent populations die at rates of 99 percent. The fatality rate for COVID in humans (one percent) is the same as the survival rate of populations of wildlife affected by disease, such as plague in prairie dogs. That’s just the way we look at things as a species. It’s not difficult to understand why, but it’s an interesting phenomenon.

I don’t want to seem insensitive about the large loss of life in the U.S. due to COVID-19—that’s a serious matter. It’s just a matter of contrasting the way we look at that, versus the way we look at much more serious disease problems in wildlife populations. We shrug off 99 percent mortality in some species of rodents. Though, maybe we wouldn’t if everybody knew what was happening.