BATAVIA (CBS) — The bison herd at Fermi National Accelerator Laboratory has gotten bigger.

Five calves were born in the past few weeks, and visitors are welcome to see the herd that now has 25 bison, the lab said in a news release.

The lab started raising bison in 1969, when Fermilab’s first director, Robert Wilson, established the herd as a symbol of Midwestern prairie history and the lab’s pioneering research in particle physics.

In 1989, the U.S. Department of Energy designated the 6,800-acre Fermilab site a National Environmental Research Park.

There are now 1,100 acres of reconstructed tallgrass prairie and seven particle accelerators at Fermilab.

Visitors can hike the half-mile Interpretive Prairie Trail and see the Leon Lederman Science Education Center with exhibits about the prairie and hands-on physics displays.

Admission to Fermilab is free, but visitors must present a valid photo ID.

Fermilab invites visitors to see the new calves in its bison herd. Visitors can also hike and learn about physics at the lab. (Credit: Fermilab)