FRANKLIN GROVE, Ill. (AP) — Straddling the line of Ogle and Lee counties are 3,500 acres of prairie where the bison roam and species of butterflies freely land on plants as rare as they are.

The bison aren't just grazing; they're part of an ongoing restoration at Nachusa Grasslands to get the regional prairie grasslands back to the way they were. Today, only a trace of Illinois' original prairie exists in spots throughout the state.

The bison are a tool for prairie restoration, said Elizabeth Bach, the property's ecosystem restoration scientist. "It needs some disruption to thrive."

Scientists...