The bison need to be herded into corrals once a year for animal veterinary work and monitoring. (Ferran Salat photo)

Nachusa Grasslands: Where the Bison Now Roam

For the first time in almost 200 years, a herd of wild bison is roaming land east of the Mississippi River. Jon McGinty explains how these mighty animals — so symbolic of America’s heritage — are helping to restore prairie.

The bison need to be herded into corrals once a year for animal veterinary work and monitoring. (Ferran Salat photo)
The bison need to be herded into corrals once a year for animal veterinary work and monitoring. (Ferran Salat photo)

For the first time in almost 200 years, a herd of wild American bison is roaming the prairie east of the Mississippi River … and it’s right here in northern Illinois. Last October, employees and volunteers at The Nature Conservancy (TNC), one of the world’s largest environmental organizations, released 30 bison at Nachusa Grasslands, the organization’s 3,500-acre tallgrass prairie restoration northeast of Dixon, Ill.

Scientists estimate that around 30 million bison roamed North America, from the northern Rockies to the Appalachian Mountains, when Columbus bumped into the continent in 1492. Plowing up the prairies, crisscrossing the continent with railroads, wholesale slaughter by hunters (many taking only tongues or hides) and other human activities reduced their numbers to less than 600 in the U.S. by 1888, when some conservation efforts began.

“As significant as the bison’s arrival here is, Nachusa is not about bison – it’s about prairie conservation and restoration,” says Bill Kleiman, project director at Nachusa Grasslands. “Bison are an important species for the prairie, a ‘grazing tool.’ But this project is much more than that.”

As Kleiman explains, bison and the prairie are inextricably linked and depend on each other for their survival. Over 200 years ago, there were more than 250 million acres of natural prairie in the Midwest, 22 million in Illinois alone – 60 percent of the land within the state. That’s why Illinois is called the Prairie State. But by the beginning of the 20th century, less than one percent was left, and by the 1980s, less than one-tenth of one percent remained.

“A statewide inventory was done in the 1970s to determine how much virgin prairie was left and where it was,” says Kleiman.

Small parcels, called remnants, were found throughout Illinois – on rocky knobs, in marshes or forests – places where farming wasn’t practical – or in protected areas like cemeteries and railroad rights-of-way. By the mid-1980s, TNC was thinking “big and bold,” wondering if they could purchase such remnants and restore the land between to recreate larger tracts of prairie.

“This site at Nachusa was chosen for such a project because it had a lot of remnants – tallgrass, wetlands, oak savannas,” says Kleiman. “That was in 1986, and by the end of that year, they had purchased 400 acres. Now, almost 30 years later, we own over 3,500 acres. We have painstakingly tried to recreate the original habitat types that were here. It wasn’t easy, or cheap. It’s been like putting Humpty Dumpty together again.”

TNC estimates that more than 430,000 volunteer hours have been spent at Nachusa, gathering seeds by hand (6,500 pounds annually), seeding and over-seeding former farmland, removing invasive non-native plants, conducting prescribed burns to control brush encroachment and removing drain tile to restore natural wetlands.

“Natural areas in Illinois are always going to need human care to survive,” says Kleiman.

Nachusa Grasslands is widely acknowledged to be one of the best prairie restorations in the country. In addition to the tallgrass prairie, the area includes savanna woodlands, fens, potholes, sandstone outcrops and rocky meadows. Naturalists have identified more than 725 species of plants within Nachusa’s boundaries, 180 species of birds, and much other wildlife such as beavers, badgers, foxes and coyotes. So, what’s missing?

“What makes grasslands occur on this planet Earth is a dry climate, periodic fires caused by lightning or human activity, and grazing,” says Kleiman. “Grazing and grasslands are connected through their evolutionary history. Prairies (one form of grassland) need grazing just like they need fire, to mimic the original ecosystem.”

According to Kleiman, bison will naturally perform “conservation grazing” as they move about the landscape, seeking new growth patches of grass. The herd will maintain a number of these “grazing lawns” throughout the growing season. When fires occur, the lawns don’t burn since there is little grass left. The next season, the herd randomly picks new growth areas for food, creating a patchy diversity of the landscape, and encouraging other plants to thrive.

Additional bison behavior is expected to increase and protect the diversity of plants and animals at Nachusa. When bison wallow in mud or dust to rid themselves of parasites, these depressions in the ground can fill with rain water, providing habitat for amphibians. As they travel from place to place, bison hooves disturb the soil and vegetation, opening spaces for wildflowers and annual plants. Seeds caught in their wooly fur get distributed widely as they move about, and their dung is nutritious for plants and some insects. They also rub their horns on young saplings, which inhibits the growth of trees.

Today, approximately 500,000 bison live in North America, almost half in Canada. They are found in all 50 states, primarily as part of growing agricultural businesses where they are raised for human consumption. There are around 30 commercial bison-raising operations in Illinois, most with small herds of 40 or less. About 30,000 bison exist on public lands, including environmental and government preserves.

The Nature Conservancy has a long history of keeping bison on its preserves, and has managed them for at least three decades. Today, TNC preserves are home to about 5,500 bison in 13 locations. Nachusa Grasslands is the only one located east of the Mississippi.

Jeffrey Walk, Illinois science director for TNC, notes that there are three main threats to the evolutionary health of the American bison: small population size, genetic introgression (in-breeding of other species, like cattle) and artificial selection. When their numbers were severely reduced in the 1800s, bison went through a genetic “bottleneck,” since all future animals were descended from those few ancestors and their genes. According to Walk, a population of at least 1,000 is needed to ensure 90 percent genetic diversity for the next 200 years.

Over the decades, meat producers have frequently cross-bred bison with domestic cattle, hoping to improve their product. This has led to adverse effects on the growth rate and water-use efficiency of bison that still carry the cattle genes. And interfering with the breeding process has caused some offspring to lose aggressive behavior that may be an advantage to a domestic meat animal, but detrimental to a wild animal.

Kleiman says there are three main sources of bison with good genetic diversity and a minimum of genetic introgression from domestic cattle: Yellowstone National Park in Wyoming, Elk Island in Canada, and Wind Cave National Park in South Dakota. The Wind Cave herd was created by the efforts of William Hornday, an American zoologist. In 1903, while he was director of the Bronx Zoo, Hornday brought several bison from out west to the zoo to preserve the species, which was then on the brink of extinction. In 1905, Hornday and Teddy Roosevelt formed the American Bison Society to help with that task, and in 1913, Hornday transported several bison to Wind Cave National Park to begin a new herd. DNA testing has determined the Wind Cave herd contains few or no cattle genes. The Nachusa Grasslands animals came from Wind Cave and other TNC preserves, which were descendants of that same herd.

In preparation for the introduction of bison to Nachusa Grasslands, Kleiman and Cody Considine, restoration ecologist at Nachusa, visited several TNC preserves to learn about dealing with these wild animals.

“We worked as volunteers at several sites,” says Kleiman, “helping them with their annual roundups and inspecting their facilities.”

While the bison herds are kept as wild as possible with little or no human contact, once a year they need some basic veterinary work done: giving medicine as needed, drawing blood samples for genetic testing, installing microchip tags in each new animal for record-keeping purposes and attaching GPS tracking collars on some for scientific study on how the animals use the preserve.

To facilitate this process, the bison are rounded up into a corral, using trucks, ATVs or horses, or they are enticed into the enclosures using “range cubes,” compressed (but tasty!) protein pellets. One by one, the animals are led into a squeeze chute, a confinement apparatus that safely holds the bison stationary while the veterinary work is done. In order to get the bison into the squeeze chute, Nachusa and other TNC facilities use a unique device called a Berlinic Cube, named after its inventor.

“A bison doesn’t want to enter a narrow confine,” says Kleiman. “The Cube consists of a cluster of movable gates, with someone standing above the animals to control the gates. The operator lets the bison go where it wants, but keeps offering the squeeze chute as an alternative. They work with the animal, instead of pushing it, patiently waiting for it to choose the squeeze chute on its own.”

Last October, 30 bison were transported to Nachusa from TNC sites in Iowa, South Dakota and Missouri, all descendants from that Wind Cave herd. A paintball gun was used to mark calf/cow pairs, so family members wouldn’t get separated. Upon arrival, the animals were “soft released” into their new home by spending some time in the corral, then a 10-acre trap pasture, next a 40-acre pasture, and finally into the 500-acre North Bison Unit, where they are now. Some time next year a box culvert will be completed under Stone Barn Road, connecting the North Bison Unit with another 1,000 acres to the south, allowing the herd to graze throughout the entire 1,500 acres of prairie.

“We saw a lot of bison corrals, and took the best ideas from several to design our own,” says Kleiman. “Our corral contains several curves and zig-zags, since bison are likely to balk and turn around if they spot a dead end of an enclosure. Temple Grandin, the well-known designer and consultant for livestock enclosures, saw and approved of our design. She’s probably going to visit us in the next year or two.”

Nachusa Grasslands has increased its science budget five-fold in order to gather good baseline data to measure the impact the bison will have on the preserve. Last year, staff set up nine bison exclosures, small areas in the bison unit surrounded by electric fencing. Then they collected vegetation data inside and just outside the areas, so comparisons can be made later as the animals roam the unit. Special six-foot high fencing now surrounds the North Unit: wire fencing on T-posts, augmented by metal posts made of repurposed drilling pipe every fourth post. The same fencing will be used to enclose the South Unit by the end of this year.

To keep the right balance of animals in the herd, the Nachusa staff will monitor data such as genetic diversity, age and sex ratios at each annual roundup. They will then decide which animals to send to other TNC preserves or private bison herds, and which to keep.

“We are cooperating with five other TNC preserves, all with animals from the Wind Cave herd,” says Kleiman. “Since we are all hosting Wind Cave lineage animals and sharing them with each other, we basically have one large genetic population of more than 1,000 animals. We can’t physically connect the sites, but we can connect the animals.”

So, why do all this?

“Illinois citizens want to be part of a global effort to keep their natural inheritance going,” says Kleiman. “Humans dominate the planet, and most species are here at our whim. We decide what’s going to stay or go. I think it’s ethical and appropriate to protect and manage these habitats for future generations.”

12 Bison Facts

1. American bison are often mistakenly called buffalo. Buffalo (sometimes called water buffalo) are a separate species, native to Africa and Asia.
2. Bison are the largest land animal in North America. Adult males stand up to six feet at the shoulder and weigh between 1,000 and 2,000 pounds. The two largest bulls at Nachusa weigh 1,700 pounds each.
3. Bison live 15 to 20 years in the wild.
4. Bison can run up to 35 miles per hour, outrun a horse and jump six feet into the air.
5. Bison feed mostly on grasses and sedges (marsh plants), consuming about 30 pounds a day. Their daily schedule usually includes two-hour periods of grazing, resting and cud-chewing, then moving on to another area to graze again.
6. Bison are social animals that live in matriarchal herds where the cows lead herd movement, and maintain contact with each other using hog-like grunts.
7. The mating season is July through September, when bulls fight one another for cows.
8. The gestation period is about 9.5 months. A single calf is born to a cow, which suckles for about one year and remains with its mother for three years (females) or up to six years (males).
9. Bison utilize water better than cattle and will travel up to eight miles to find a source. Cattle will usually travel only about a mile to seek water.
10. Bison can survive in an open area in weather up to 40 degrees below zero, before needing shelter.
11. Bison have relatively poor eyesight, but a keen sense of smell.
12. Bison are usually mild-mannered, but can become aggressive.

Visitor Expectations

Nachusa Grasslands is located four miles northeast of Franklin Grove, Ill., with headquarters and visitors entrance on Lowden Road south of Stone Barn Road. For driving directions or volunteer information (there are volunteer stewardship activities almost every Saturday during the warmer months), go to or The Nature Conservancy’s website at There are numerous hiking trails throughout the area (not in the bison units), and the preserve is a favorite for birders and wildflower enthusiasts. No pets allowed.

There is also a hiking app for smartphones that provides a guided narration for some of the trails. It can be found on the websites mentioned above.

The bison are in 500 acres of gently rolling landscape bounded by Flagg Road on the north, Lowden Road on the east and Stone Barn Road on the south. The animals are not always visible from public roads, and there are not yet any pull-offs, but Stone Barn road is a dead end, so there is little traffic. Bring binoculars and telephoto lenses for your camera.

If you view the animals from outside your vehicle, be respectful of the distance between you and the bison. Longtime volunteer Betty Higby says: “If the bison walk away from you, you’re too close. If their tail is up, they’re not happy, and you should move away. If they start pawing the ground and putting their head down, it may be too late!”