Prairie dogs, especially the bigger ones, apparently like peanut butter.
About 70 percent of wild prairie dogs successfully ingested peanut butter flavored baits containing an oral sylvatic plague vaccine that were distributed throughout their habitats, according to a new U.S. Geological Survey study.
"We felt really good to get 70 percent uptake," said Randy Matchett, a U.S. Fish and Wildlife Service biologist at the Charles M. Russell National Wildlife Refuge, who helped author the study.
"At a couple of individual sites in Wyoming we got 100 percent," he said, whereas in some prairie dog towns in Utah it dipped to 50 to 60 percent.
Sylvatic plague can decimate prairie dog populations, which in turn affects the recovery of endangered black-footed ferrets that depend on prairie dogs for food. Protecting wildlife from plague and reducing spread of the disease can also help people and pets that are susceptible to infection.
“Wildlife managers can use these findings to develop SPV-baiting strategies that maximize consumption and immunization in targeted prairie dog populations,” said Tonie Rocke, a USGS coauthor of the study.
The USGS partnered with Colorado Parks and Wildlife and the U.S. Fish and Wildlife Service on the new study.
In a large-scale, three-year field trial, scientists with the USGS and other state and federal partners distributed the peanut butter-flavored baits at 12 locations near active prairie dog burrows in Arizona, Colorado, Montana, South Dakota, Texas, Utah and Wyoming.
Matchett worked with Kurt Kreiger, owner of the Billings company Model Avionics, to design a distribution system for the gumball-like baits. The thrower resembles those used in tennis ball and baseball-throwing machines — a couple of spinning wheels sends the pellets flying.
Then they adapted the distribution system to fit a large drone as well as ATVs so that one person could spread bait across the landscape more quickly.
This summer, Matchett's crew treated up to 100 acres an hour on an ATV, about 60 acres an hour via drone, "which is still pretty good," he said.
Matchett also discovered the system for making the round baits, which was based on a Lithuanian carp bait machine known as the BoilieRoller.
Although the baits are for the most part similar, flat spots created when the balls sat and dried could lead the distribution system to jam.
When processing of the baits was turned over to a U.S. Department of Agriculture facility in Idaho, another problem cropped up. Some baits were too large. So, as in the past, Matchett and Krieger collaborated on a sieve system to weed out the large baits that could jam the machines. The high-tech device was a piece of plastic with proper-sized holes cut in it which was then taped to the bottom of a box.
To get rid of broken chunks, they created a cattle-guard-like sieve that lets the pieces fall through.
"That solved 99.99 percent of the jamming problems," Matchett said.
Out of 80,000 baits he received, about 1.5 percent were too big, which is actually a pretty low rate, he pointed out.
"But in the distribution process that's 800 jams."
A harmless dye was incorporated into the baits that, once ingested, is viewable under certain microscopes. The scientists sampled hair and whiskers from 7,820 prairie dogs for presence of the dye to determine which animals had eaten the baits.
"(The dye) shows up in two or three days in their hair and whiskers," Matchett said. "In two weeks it sticks out like a sore thumb."
Results are in
“The results showed that heavier prairie dogs were more likely to eat baits than smaller animals, and for most prairie dog species, the quality and density of vegetation such as grass influenced bait consumption,” said Rachel Abbott, a USGS scientist and lead author of the study.
Overall bait consumption, or uptake, ranged from 68-72 percent during the 2013-2015 sampling period, although uptake rates varied by species. The scientists also found that vegetation in the prairie dog colony and the day of baiting affected consumption for black-tailed, Gunnison’s and Utah prairie dogs. For those three species, baiting later in the season, when green vegetation is less dense, can improve the ingestion rates by smaller animals.
Matchett called these findings, about low bait consumption when green vegetation is available, the biggest finding of the study, and also one of the most complicating.
Baiting in May results in about a 20 percent consumption of the bait. Waiting until July or August, however, means that a new pulse of prairie dogs — those born that spring — have not been vaccinated. That means that following spring up to half of a colony may not have been immunized.
Like a flu vaccine for humans, not everyone needs to be vaccinated to slow the spread or outbreak of the illness, Matchett noted, a term known as herd immunity. However, wildlife biologists aren't sure what percentage of prairie dogs would have to be vaccinated to create herd immunity.
"That's where we're stuck," he said.
"As with any innovative project, you live and learn," Matchett said. "There's no shortage of obstacles. Kurt and I have a huge pile of stuff that hasn't worked."