In 1987 thirty animals donated by Fort Riley Military Reservation were introduced onto Konza Prairie. Herd size increased over the years through reproduction, additional donations, trades and purchases. On Konza Prairie the standing bison herd averaged 300 from November of 2005 to November of 2011. The land designated to the herd is about 2400 acres of fenced tallgrass prairie. The herd is part of the long-term ecological research of Konza Prairie Biological Station where fire, grazing and climate are studied in the tallgrass prairie ecosystem. Grazing is an important ecological process. The effects of bison behavior are of interest as they graze and live as naturally as possible on the prairie. Therefore the herd is not supplemented by man and does not receive the kind of care that domesticated cattle require to survive. Cows weigh about 860 lbs and bulls 1800 lbs. Old bulls, especially those on supplemental feed in private herds, can reach 2000 lbs.

The number of calves born from November 2005 to November 2011 averaged 90. Calves weigh about 50-60 lbs. at birth. The calving rate averages about 66%, ranging from 44% in 2004 to 83% in 2007.  (Cows are of reproductive age at 3 years and older.) Mature cows generally produce two calves in a three-year period. Severe winters can reduce calving rates significantly. The number of female and male calves born each year follows the expected 50:50 ratio. A newborn calf may begin to suckle about 20 minutes after birth. After a long drink of about 30 minutes the calf is able to follow it mother as she drifts away from the birth site.

A roundup takes place in October or November at Konza Prairie. New calves are ear-tagged and weighed. All calves are kept through their first year. Some older animals are culled during roundup by a process resembling natural attrition. Both young animals and old, low-vigor animals and excess males are removed for sale at a regional bison auction and to private buyers. Sale animals are tested for brucellosis. Other data on bison health have been collected by the Kansas State University veterinarians.

All KPBS bison calves receive ear tags at the fall roundup when they are about six months old. The tags are numbered and color-coded to keep track of the age of the animal, its origin and affiliation to other members of the herd. The color of the tag designates the decade of birth, for example, white tags represent the years from 1990 to 1999, whereas yellow tags represent animals born from 2000 to 2009, and orange tags indicate animals born in 2010 or later. The first number on the tag is the year of birth. The following two numbers are the individual’s id.

Historically, bison were the primary grazers of the prairies and played a keystone role in the ecology of the grasslands. Herd management on Konza Prairie is all about having a standard grazing effect on the prairie ecosystem. Light grazing intensity is set at 25% removal of annual aboveground plant biomass in a 12-month period. Unlike most cattle operations in the Flint Hills of Kansas, bison remain on the prairie year-round. In the Flint Hills yearling cattle graze from May through September and generally are taken off pasture in October and sent to feed lots to finish. Although it is difficult to directly compare the two types of animals, grazing comparison trials of bison and cattle have been ongoing for 10 years. To accurately compare bison to cattle, weight, not age, is the important factor. Bison grow more slowly than domestic cattle. Two-year old bulls weigh about as much as yearling domestic cattle. Comparison trails are based on weight gains in the May to October (five months) growing season. Bison and cattle graze in separate fenced areas with equivalent stocking rates. Cattle are from the cow-calf herd of the KSU Department of Animal Science. Although there are some differences in how bison and cattle affect prairie vegetation, most of these differences are due to how the animals are managed. Cattle kept on pasture over winter are fed where bison are not. Unsupplemented bison tend to loose about 11% of their summer weight during the winter. Unsupplemented domestic cattle would die. Suckling calves will gain about 3% during the winter.

Bison and cattle are not functionally equivalent. Bison maintain large grazing lawns. They return again and again to the same “lawns” to eat the new growth of grass, which is highly nutritious. These areas may look overgrazed but actually have new growth continually, providing the nutritious grass bison need, even if only one inch high. In moderately stocked pastures, cattle tend to graze smaller patches distributed more uniformly throughout the pasture. Plant diversity is greater in bison pastures than in cattle pastures. Forb numbers, especially annuals, are higher in bison pastures. Both bison and cattle primarily consume Big Bluestem, Little Bluestem and Indiangrass on the tallgrass prairie. Cattle remove about 46% of the annual net primary production of the grasses while bison remove about 54%.