WASHINGTON (CN) – Drone-delivered plague vaccine could save colonies of prairie dogs, the main prey of black-footed ferrets, the most endangered mammal in the United States, federal agencies say. The U.S. Fish and Wildlife Service announced that it has completed two Environmental Assessments proposing to administer oral plague vaccine to prairie dogs in the Charles M. Russell and UL Bend National Refuges in northeastern Montana, and proposing to do so using unmanned aircraft systems (UAS), or drones.
Black-footed ferrets, the only ferret species native to the U.S., historically numbering in the tens of thousands, were once believed to be extinct. In 1981, a wild population was discovered in Wyoming, but disease nearly wiped out the colony, the Service said. The few surviving ferrets were captured for a breeding program, and those captive-bred animals have been used to reestablish colonies in 27 sites within the historical range, from southern Canada to northern Mexico in parts of 11 Midwestern states. “Approximately 300 ferrets were known to exist in the wild at the end of 2015,” the agency said.
Captive-bred animals are vaccinated against plague before they are released, and the USFWS continues to capture and vaccinate young ferrets in the newly established populations. However, if there is nothing for them to eat, that effort is pointless.
In the U.S., the ferrets depend on three species of prairie dogs for food, and they use the rodents’ burrows for shelter. Considered a pest by farmers and ranchers, the numbers of prairie dogs have been severely reduced from historical levels, which led to the near-extinction of the ferrets. Many other species also depend on the prairie dogs, such as burrowing owls, mountain plovers, swift fox, eagles and badgers, according to the a U.S. Geological Survey fact sheet.
Reestablishing ferrets depends on maintaining healthy populations of prairie dogs, which are highly susceptible to plague, an introduced disease, to which the animals have no natural immunity. An outbreak can wipe out 90 percent or more of a colony and can lead to local extinctions.
Though it is the same disease that killed millions of people in Europe in the 1300s as bubonic plague (infected lymph nodes), septicemic plague (blood infection) and pneumonic plague (infected lungs), it is termed sylvatic plague in wildlife. While pneumonic plague can be easily spread people-to-people by coughing, sylvatic plague is most often spread through flea bites, the USGS said.
Individually injecting prairie dog populations is not feasible, and fortunately, they do well with the newly developed oral vaccine, which is absorbed in the mouth as they eat the peanut-flavored baits, the USFWS said. “Defenders of Wildlife and many others have spent a lot of time and money over the last 30 years to save the black-footed ferret from extinction, but without a successful plague vaccine for both prairie dogs and ferrets it may all be for naught,” Jonathan Proctor, Defenders of Wildlife’s Rocky Mountain region representative, said. “This work is absolutely critical to save our nation’s investment in black-footed ferret recovery.”
Previously, the U.S. Forest Service attempted to control the threat to prairie dog colonies by dusting the areas around the colonies with pesticide, which is labor-intensive, costly and must be repeated yearly, the Forest Service said. Another concern is the fleas’ suspected pesticide resistance to chemical control, the USFWS said.
The Forest Service has been field-testing the new vaccine approach that was jointly developed by the USGS’s National Wildlife Health Center and the University of Wisconsin-Madison. “An oral vaccine can be delivered much more efficiently to large numbers of animals, because we are putting it in bait that we can broadcast widely from planes, trucks or other vehicles,” wildlife biologist Tonie Rocke of the U.S. Geological Survey National Wildlife Health Center, said.
The USFWS, in its Environmental Assessment, made clear that its preferred method of vaccine distribution is through the use of drones. During trials, the sylvatic plague vaccine (SPV) was applied by hand by people walking pre-defined transects dropping baits every 9-10 meters. All terrain vehicles could speed that process, but would also create negative environmental impacts. Depending on terrain, a single person could treat 3-6 acres per hour, the agency said. “If the equipment can be developed to deposit three SPV doses simultaneously every second, as we envision is possible, some 200 acres per hour could be treated by a single operator. For SPV to be a viable plague mitigation tool at meaningful management scales for ferret recovery, delivery via UAS is potentially the most efficient, effective, cost-conscious and environmentally friendly method of application,” the agency noted.
Comments on both Environmental Assessments are due May 13.
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