Calving season at the Nachusa Grasslands occurs primarily in April and May. Most cows have a single calf following a gestational period of 285 days, about 9½ months.

Calves are cared for by their mothers for about nine months. This period is crucial for the survival of the calves and is influenced by several ecological factors.

The presenter for the Those Were The Days program at the Oregon Depot at 10 a.m. Saturday, April 25, will be Oregon resident Mark Herman.

A Nachusa Grasslands volunteer, Herman will talk about the history and evolution of the critical grassland habitat, which the Nature Conservancy has protected and restored since 1986. Herman will also talk about the return of wild bison to the Illinois prairie in 2014.

What began as small prairie remnants and oak savannas interspersed with cornfields, has been carefully managed and restored to more than 4,000 acres of prairie, woodland, savanna and wetland habitats. In 2014, the first wild bison herd in Illinois was brought to the Nachusa Grasslands to complete the tallgrass prairie ecosystem.

Nachusa Grasslands is a community-based volunteer-supported operation and has become a model for habitat restoration and science research.

Herman is the former superintendent of education at the Byron Forest Preserve District in Byron and curator of education at Midway Village Museum in Rockford. He is an active volunteer with The Nature Conservancy’s Nachusa Grasslands, Middle Rock Conservation Partners and the Chana School Museum.