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Fermilab Bison: a Prairie Native

Bison - in the past they roamed the North American prairies and plains in vast herds. Estimates of their numbers in 1850 range from 20-50 million. Hunting, changes in land use and government policies brought the bison near to extinction. By1889 there were about 550 bison left. Today there are an estimated 150,000 bison in North America. They are no longer endangered. Fermilab has played a role in the bison's resurgence by maintaining a demonstration herd.

The Fermilab herd is part of the Lab's program to recognize the history and prairie heritage of Illinois. The tradition was started in 1969 by Fermilab's first director, Robert R. Wilson, who wanted to give local residents an opportunity to enjoy the natural environments of Illinois. He also felt that international visitors would appreciate seeing this piece of Americana. The subsequent directors, Leon Lederman and John Peoples, Jr. have continued the commitment to the bison herd and other environmental programs.

The animals in the Fermilab herd are American bison (Bison bison). Many of us call these animals "buffalo," a term which comes from the French word, "boeuf," meaning ox or beef. When French trappers saw the bison herds, they reminded them of the cattle back home. However, bison differ in several ways from buffalo which are native to southern Africa and Asia. For example, there are differences in the shape of the horns and the number of ribs.

The Fermilab herd is kept in a fenced pasture. These 80 acres are enough to support about 70 head, however the size of the herd varies seasonally. Through the winter the herd consists of 40-45 animals - currently 4 bulls and the rest cows. In the spring 25-35 calves may be born, bringing the herd to the carrying capacity of the pasture. In the fall about 30 animals are sold to bring the herd size back to about 40 for the winter. Every few years the bulls will be sold and new bulls purchased to maintain the genetic health of the herd. Fermilab bison have a reputation for being large and healthy animals and are much sought after by breeders. The sale of the bison covers a portion of the expense of maintaining the herd.

In the wild, bison eat mostly grasses, small plants and twigs of some shrubs. Similar to cows in that they have four stomachs, the bison swallow the grasses whole and then bring up the partially digested food and chew their cud. At Fermilab the bison herd is unable to move to fresh pasture; their diet is therefore supplemented with hay grown on the Lab property and with protein and vitamin pellets formulated for dairy herds.

Male bison grow significantly larger than female bison. A bull can be 6 feet high at the shoulders and weigh up to 2000 pounds. A cow is closer to 4 1/2 feet high at the shoulders and 900 pounds. Calves weigh about 45 pounds at birth.

Bison hair grows in two layers. There is a thin layer of soft fine hair and an outer layer of coarse thick hair. The short fine hair is insulation for the winter. In the spring the bison shed their hair in large clumps making them look extremely shaggy. In the fall, they grow a new coat.


Both bulls and cows have horns. The horns are actually a hollow cap which grows over a bone-like core. This black horny cover is a growth of modified hair protein which grows one layer a year beginning at age 4. While the open end of the horn-cap is hollow, the pointed end is solid. The tip develops a sheen due to polishing by rubbing and digging. The cap may be accidentally broken off when the bison digs in the mud. It does not grow back, but the short core hardens and remains.

The bison herd has a dominant male and a dominant female. The dominant bull is usually the largest and strongest. He is allowed to mate freely. At times another bull may challenge his dominance and a shoving and head butting match will ensue to determine whether there will be a new dominant male. However, it is the dominant cow who really leads the herd. She determines when and where the herd will move by her actions, which the rest of the herd follow. The dominant cow is usually the oldest and largest. Currently at Fermilab, the dominant cow is 21 years old.

You can observe the bison as they roam a fenced pasture at Fermilab. Stop by the side of the road and watch the behavior of these very American animals.
For more information and pictures of buffalo check out the Fermilab Flora and Fauna Exhibit at: http://www-ed.fnal.gov/entry_exhibits/main_title.html