The female bison begin giving birth in late April and at least 10 baby bison are expected to be born over the next six weeks.
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This bison herd was established in 1969 by Fermilab's first director, Robert Wilson, as a symbol of the history of the Midwestern prairie.
There are 1,100 acres of reconstructed tall-grass prairie at the Fermilab site.
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The site is open every day from 8 a.m. to 8 p.m. and admission is free, but a valid photo ID is needed to enter.