Greg Schroeder picked up a distressed prairie dog that was jumping back and forth in a cage and scanned the tag under its skin to see if it had been captured before.
Bison grazed in the distance on the eastern edge of Wind Cave National Park where Schroeder was capturing the prairie dogs and carrying them to a trailer where they would be sedated as part of an effort to immunize them against disease.
After they were sedated, the prairie dogs were weighed, measured for height, tested for fleas and then a whisker sample was taken. The whisker was then viewed under UV light to see if a vaccine, previously embedded in gelatin bait, was present to prevent the spread of sylvatic plague.
Sylvatic plague is a form of bubonic plague, known as the “Black Death,” according to the Black-footed Ferret Recovery Program. The disease is transmitted to other animals and people by fleas.
The threat of the disease spreading to humans is minimal now, mainly because of advanced hygiene and antibiotics. But prairie dogs are not so lucky.
All of the testing done Tuesday afternoon, which takes about 10 minutes for each prairie dog, was done in an effort to keep them alive, primarily to keep the endangered black-footed ferret's meal of choice thriving.
The black-footed ferret, thought to be extinct until 1981, feeds almost entirely on prairie dogs, even though the two species are relatively the same size, said Endangered Species Chief Bridget Fahey with the U.S. Fish and Wildlife Service.
"Think about a cow and a wolf: You've got one that's more of a grazer, not really a fighter, and you've got one that's a carnivore," she said. "They [ferrets] catch their prey essentially by their fierce grasping jaws — they're just built for it. They're very cute, but they're very fierce."
Generally, efforts to stop the spread of the disease in prairie dogs occur through dusting individual burrows with pesticides to kill infected fleas. Work has now shifted to field delivery of the vaccine through bait, which can last at least nine months, according to the National Wildlife Health Center.
Although an outbreak of the plague has not been seen in Wind Cave National Park, the disease was found in southeastern Custer County in 2004; in Pine Ridge in 2005; and at the Conata Basin in 2008, said South Dakota Field Supervisor Scott Larson with the wildlife service.
"We saw really rapid decline in prairie dog populations in Conata Basin, where we also have ferrets," he said. "If these trials prove successful, the idea is that it can be another tool to hang on to some prairie dogs where we really want them and where we want ferrets."
This summer marks the second year of a three-year study, with 34 sites in seven states all distributing the vaccine and then testing prairie dogs, said David Bergman with the U.S. Department of Agriculture.
There are also two other testing sites in South Dakota, one near Wall and the other in Lower Brule, Schroeder said.
Although there is a vaccine for the black-footed ferret to fight the sylvatic plague, Fahey said it is challenging to administer the vaccine once the animal is wild.
"Controlling the disease is one of the most difficult things," she said. "The number one thing we can do, because [the ferrets] do rely on prairie dogs for food, is to be able to keep enough prairie dogs alive at our reintroduction site so they can survive into the future."
Ultimately, Fahey hopes to get the black-footed ferret introduced in all 11 states in its native range.
"Anything we learn (in South Dakota) — how to slow or control the spread of plague — is going to be applicable to our program overall," she said.
The prairie dog is vital to more animals than just the black-footed ferret. Animals such as bison and owls also depend on prairie dogs, which landowners sometimes view as pests, Larson said.
"Owls live in their burrows too, but there are a number of animals that either live in the prairie dog towns or live near them," he said. "Vegetation also tends to stay greener for bison because the prairie dogs clip it so it stays green longer."
Results for the study are expected in 2016 at the earliest, and if successful, will be regulated as an experimental vaccine for use by government agencies.