Bison travel in herds, grazing on grasses and leaving other plants alone. Areas with shorter grass and abundant wildflowers attract nesting birds and prairie insects. Prairie chickens forage on the ground, feeding on insects and plant material.
Paleontological and archaeological evidence documents the early presence of bison. The oldest bison bones in Illinois date to the Ice Age. Bison fossils in northern Illinois peat deposits date to 9,000 years ago. Remains found in the Illinois River valley show that small herds were in central Illinois by 4,500 years ago. Bones are rare, but occur in Native American sites of 2,000 years ago. They become far more common in late prehistoric times.