Pulling Hairs to Protect Bison
Genetic research on the unique Wind Cave bison population is helping TNC and partners manage and protect bison and the prairies where they live.
At the Wind Cave National Park bison round up this fall, these iconic mammals went through one extra step before they headed out to Nature Conservancy preserves across the country—a quick sample was taken from their tail hair.
So why would anyone want to pull a bison’s hair out?
"Having samples of the bison’s tail hairs allows researchers to analyze the animal’s genetic makeup, so that we can ensure there’s good diversity at each of the Conservancy’s herds,” explains Corissa Busse, The Nature Conservancy’s western South Dakota conservation manager who facilitates the bison exchange between Wind Cave and TNC.
Establishing Satellite Herds
Over a decade ago, Wind Cave and TNC entered an agreement through which the National Park started sending animals to TNC preserves after their biannual roundup. The exchange not only gave TNC project managers the grazing animals they needed to keep prairies and other habitats healthy, but it ensured the health of the Wind Cave bison herd, which along with the bison at Yellowstone are among the only herds that to date have shown no trace of cattle genes in their DNA. In addition, Wind Cave animals have a high rate of unique genetic traits not found in other herds.
“In the studies we’ve done over the last 20 years, it’s become clear that there are some legacy bison herds that are truly important to the conservation of the species and one of those herds is the herd at Wind Cave,” explains James Derr, a professor at Texas A&M University’s College of Veterinary Medicine.
Because of its size, Wind Cave can only sustain around 400 animals, while Derr and other researchers agree that 1,000 breeding animals is the smallest population size needed to stop the erosion in genetic diversity. That’s where TNC preserves enter the picture. When Wind Cave sends bison to TNC “satellite herds” across the country, the number of breeding animals can reach 1,000.
“During the roundup, we remove 85 percent of our one-year-olds and two-year-olds,” explains Greg Schroeder, chief of Resource Management at Wind Cave National Park. “We keep 15 percent. The others will go to The Nature Conservancy or others to help with the conservation of this herd through genetic banking off-site.”
“In addition to the genetic piece of the puzzle, these satellite herds help protect the Wind Cave line in case disease spreads or there’s a catastrophic environmental event such as an extremely severe winter storm or wildfire,” he adds.
Next Steps in Bison Management
This year, bison from the Wind Cave roundup headed to TNC’s preserves in Illinois, Indiana, Iowa, Missouri and Kansas—and hopefully their numbers will grow in the future.
In exchange for the bison received from Wind Cave, TNC has also agreed to help fund new cutting-edge genetic research with Dr. Derr and Texas A&M University that will help determine if the satellite herds are showing the same genetic diversity as the “mother herd” at Wind Cave.
“There are a lot of challenges in managing bison for genetic diversity, but one thing that helps us is that everyone who works with bison feels a responsibility to be a good steward of this species,” Derr says.
“Because of land and road development, bison can’t roam the way they used to. We control their movement and their numbers. And because of that, many of us have committed to putting bison back on the landscape and manage them appropriately, and the Conservancy has made that commitment as well.”
The new genetic testing is still in development, but once it’s ready, it will compare bison from the satellite herds with 200-year-old samples from a time before bison were crossbred with cattle. It will also help bison managers create a strategy to make these herds more representative of the Wind Cave herd. In the meantime, TNC preserves are already collecting tail hairs at their own roundups, which will be saved for future analysis.
“What’s so exciting about this project is that it uses the way the Conservancy approaches conservation of land—at a whole system, landscape scale—and applies to a species,” Busse says. “We’re not just trying to save a few animals. We’re looking at how we knit together these different herds to keep the entire line thriving well in the future.”