Bison herd in Franklin Grove more than quadruples since 2014

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Bison at Nachusa Grasslands near Chicago (photo from their Facebook page)

FRANKLIN GROVE, Ill. (AP) — A herd of bison on an Illinois prairie has grown from 20 to 90 since it was brought over two years ago to boost the grassland restoration.

The 4,000 acres of prairie at the Nachusa Grasslands west of Chicago has become an attraction as volunteer work days have drawn record attendance, reports the Chicago Tribune.

Nachusa project director Bill Kleiman says 17 calves were born this year. The Nature Conservancy, an international nonprofit that owns Nachusa, may send bison to other reserves or sell some for meat next year if the herd continues to grow.

But the project has had some setbacks. In December managers ordered two bulls be killed after they escaped Nachusa and refused to return. Two calves and a female cow also died this year.