Receiving an annual health check-up can be a challenge for most humans, but imagine completing a check-up on a bison weighing almost 1,800 pounds.

That’s exactly what the ranch hands did earlier last month at the Joseph H. Williams Tallgrass Prairie Preserve, just north of Pawhuska. Consisting of almost 40,000 acres, it is the largest protected remnant of tallgrass prairie left in the world and is managed by the nonprofit Nature Conservancy.

According to Bob Hamilton, director of the Tallgrass Prairie Preserve, the 24th annual bison round-up concluded in November and the entire bison herd received a clean bill of health.

A total count of 2,393 bison, 585 of which were calves, were gathered to perform various scientific studies and receive vaccinations to ensure the health of the herd, Hamilton said.

The roundup, which takes about a week, is the only time the bison are gathered and confined on the prairie. During the roundup, all heifer calves were vaccinated against brucellosis and all keeper animals were vaccinated for several bovine diseases and treated for parasites, Hamilton said.

The herd receives no supplemental feeding, but, because the animals are in a restricted range, salt with trace minerals is provided. Water is available in creeks and ponds.

But the bison herd received some help this year from Mother Nature, after unusual summer rains drenched Osage County, bringing healthy growth to the bluestem landscape of the prairie. The largest bison that came across the scales at this year’s roundup was a 1,785-pound bull born in 2011.

“We suspect the seven inches of rain we got in August gave the prairie a late summer boost that improved forage quality and resulted in the increased body conditions for the herd,” Hamilton said.

The goal of the Nature Conservancy is to sustain the ecology of the land and the balance of animal life within the acreage of the Tallgrass Prairie Preserve. In order to do that, Hamilton said 548 bison were sold this year to keep the size of the herd within appropriate levels for the land.

According to the Nature Conservancy’s website, bull bison are sold at 6-7 years of age, since after this they tend to become more aggressive and dangerous. Cows are sold at 10-12 years of age. They are still productive through their early 20s but their sale value is higher as teenagers. Also, the older cows are less physically fit for withstanding the rigors of roundup.

Despite droughts, chilling winters, and anything else Mother Nature sends their way, this resilient herd reached its target size in 2008 of 2,700 for the summer and 2,100 for the winter. The Tallgrass Prairie Preserve bison herd started with 300 in the fall of 1993, donated by Bartlesville rancher Kenneth Adams.

The preserve is open daily from dawn to dusk and provides hiking trails and 10-mile bison loop. Visit nature.org/tallgrass to plan a trip to see the herd of bison.