Nature Conservancy Magazine: Winter 2008 - The Last Bison

Room to Roam
Once outside the corral, bison are not as yoked to water sources as are cattle, preferring instead to roam far and wide. That means they are less likely than cattle to overgraze areas near water sources or destroy streamside habitat.

“From a distance, bison resemble cattle; they look like docile grazers. But once a year, when the management takes place and you get them in the corral, you realize that they’re wild animals, not domesticated at all.”

— Bob Hamilton, director of the Conservancy's Tallgrass Prairie Preserve

Round-Up Video
Watch this video to get a taste of a bison roundup!

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“From a distance, bison resemble cattle; they look like docile grazers,” says Hamilton as he watches the bull trot away. “But once a year, when the management takes place and you get them in the corral, you realize that they’re wild animals, not domesticated at all.”

Although bison (Bison bison) and cattle (Bos taurus) are taxonomically related — they are cousins, both members of the Bovidae family, which also includes gazelles, antelope, buffalo, sheep and goats — they have distinct diets and decidedly different behaviors.

Bison eat mostly grass or sedge, with less than 2 percent of their diet coming from broadleaf forbs or flowering plants. About 30 percent of a cow’s diet comes from these rare beauties among the tallgrass.

“Big, showy forbs, like the compass plant or maximillian sunflower, are ice-cream plants for domestic livestock,” says Hamilton. “Cattle love them, and with unrestricted access they will simply drive them out.”

This subtle difference in diet selectivity means that when it comes to grassland management, all ungulates are not created equal.

“Grasslands are missing the plant and animal diversity they originally had when bison were roaming the prairies,” says Hamilton. “We want the whole bag of biodiversity here, and we’re using what works best to get it.”

Tallgrass is no buffalo ranch. Hamilton could use cattle to mow down the grasses. Others do, just beyond the fences that mark the boundary of the preserve. But it just so happens that the way bison use the landscape makes that whole bag of biodiversity possible. Besides their diet, which allows a host of prairie plants to flourish, bison provide food, habitat and even water for other animals: When bison wallow in the dust to clean their hides, the saucer-sized depressions they make collect standing water in an otherwise dry landscape.

And this habitat, prairie habitat — which has already telescoped to 1 percent to 2 percent of its original range, and is still being overrun by cows and plows — is more than just an empty landscape. Keeping bison as bison is not just about nostalgia for an ecosystem lost; it’s also about preserving the tool that makes prairies possible.

Prairie Possibilities

“662! Heifer!” shouts one of the wranglers. The animal is already in the chute, and this time Hamilton is waving a wand by its head to read a transponder tag dangling from the left ear. Each tag contains a unique code, which is used to identify the animal. The wand transmits the information to a portable computer housed in a shed nearby, which pulls up information unique to the animal, including sex, origin, age, weight and — for some bison — the results of Derr’s DNA tests.

“Cattle mitoch,” says a disembodied voice emanating from the computer, indicating that the bison in question has mitochondrial DNA from a cow.

“’05 model! She’s a seller!” calls Hamilton as the young heifer makes a mad dash for a nearby pen. Tallgrass sells its 2-year-old females with mitochondrial DNA from cattle before they can breed and pass cattle genes on to the next generation. “There may be a biological price to pay for being part cattle,” says Hamilton.

At Tallgrass, selling about as many bison as are born on the preserve each spring allows Hamilton to maintain a target population of 2,500 bison and work toward managing a herd of cattle-gene-free animals. If a bison is a “keeper!” it returns to the prairie; if it is a “seller!” it will be trucked to High Plains Bison, a range-raised, hormone and antibiotic-free bison processing plant.

For now, the odds for Conservancy bison look pretty good. Preliminary results from Derr’s lab indicate that approximately 85 percent of the bison at Tallgrass could be free of cattle genes. And there is hope that some of the other Conservancy herds will be 100 percent bison.

“We call them land sharks out here,” says Hamilton nodding toward the bison once again grazing in the distance. “When they’re on the prairie, working their way through the tall grass, all you can see is their humps, gliding along.”

In the twilight, the shaggy humps of Hamilton’s land sharks are all that’s visible among the prairie swells as a fingernail moon takes its place in the sky. No fence, no corral, no cowboy can be seen in the failing light. Only the “keepers” graze in the distance. It’s one piece of this prairie puzzle that’s back in place.

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