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20th Annual Bison Round Up Concludes at Tallgrass Prairie Preserve

PAWHUSKA, OK — This week, the 20th Annual Bison Roundup at the Tallgrass Prairie Preserve concluded with a total count of 2,642 bison, 632 of which were calves. Consisting of almost 40,000 acres near Pawhuska in Osage County, the Tallgrass Prairie Preserve is the largest protected remnant of tallgrass prairie left in the world!


Tallgrass Prairie Preserve near Pawhuska, Oklahoma | November 10, 2013

2013 Tallgrass Roundup

In the fall of 1993, 300 bison were released back to their home on the tallgrass prairie. They had a tall order to fill: help restore a portion of the tallgrass prairie ecosystem. Twenty years later, they’ve done just that and more! As the herd size grew, the bison themselves created a tall order for The Nature Conservancy: rounding up these furry beasties annually!

 “What started out as an adventure on foot quickly changed to ATV’s and now trucks which have proven to be the safest option for both bison and people. Keep in mind these animals can weigh up to a ton and run up to 35 mph!” Preserve Director Bob Hamilton said. “Over the last 20 years, we have rounded up 35,634 bison! Many of those of course were the same bison year after year.” 

The total number of individual bison that have been a member of the Tallgrass Prairie Preserve bison herd within the last 20 years is 9,137 (300 from the original herd, 8,585 were calves born at the preserve, and 252 were purchased or donated to help diversify the genetics of the herd). 

This year’s calving rate was 69%. The largest calf weighed 480 lbs. (bull, 6-8 months old), while the smallest weighed 75 lbs. (1-2 months old). 

The largest bison that came across the scales at this year’s roundup was a 1,705 lb. bull that was born in 2006.

During the annual roundup, all heifer calves are vaccinated against brucellosis. All keeper animals are vaccinated for several bovine diseases and treated for external and internal parasites. For research and record-keeping purposes,each individual bison in the herd is identified with an ear-tag transponder.

A total of 634 bison from this year’s roundup were sold in order to keep the size of the herd within the appropriate ecological stocking rate. Bulls 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.

Preserve staff expect another 600-700 bouncing baby bison to be born in the spring of 2014!

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The chart below shows the growth of Tallgrass Prairie Preserve bison herd since 1994, including the number kept on the preserve over the winter, as well as the number of calves born the following spring. The number of calves is determined at the fall roundup, when each animal is examined, weighed, and inoculated. The fall roundup, which takes about a week, is the only time the bison are gathered and confined on the prairie. The roundup permits the Conservancy to perform various scientific studies and ensure the health of the herd. 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 (includes calves) and 2,100 for the winter.

2013 Tallgrass Roundup


The Nature Conservancy is a leading conservation organization working around the world to conserve the lands and waters on which all life depends. The Conservancy and its more than 1 million members have protected nearly 120 million acres worldwide. Visit The Nature Conservancy on the Web at www.nature.org

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