Bison are part of the tall grass prairie ecosystem. Before becoming the Tall Grass Prairie Preserve, the land had been used to graze cattle by the Chapman-Barnard Ranch.

Christina Adams Bison Herd

Inception of the Tall Grass Prairie Preserve bison herd occurred in October 1993 with the release of 302 bison. The starter herd is complete comprising:

• 125 Cows
• 9 Bulls
• 28 Two-year olds
• 46 Yearlings
• 94 Calves

These animals were a donation from Ken-Ada Ranches Inc., owned by Kenneth and Diana Adams. The herd was given in honour of their daughter Christina. Created in 1985, the Ken-Ada herd was developed by acquiring animals from a dozen different private and public herds throughout the west and midwest. Before the herd was transferred to Tall Grass Prairie Preserve, it was certified free from tuberculosis and brucellosis (bangs).

Each bison is implanted with a state-of-the-art transponder at the base of the ear, an invisible identification system. Staff use these transponders to monitor information about each bison, including yearly weight, calving success, service, and age. External, plastic ear tags indicate the animal's bangs test number. Each transponder contains a unique 10-digit code that works much like a bar-code at a grocery. A paddle connected to a computer generates an electromagnetic field to read the code when it is held in vicinity of the transponder attached to the bison. Handling bison is very dangerous. This computer technology enables staff to gather accurate data quickly, reducing the risk of injury to the cowboys and the bison.

On the Tall Grass Prairie Preserve the herd of bison will grow in size to 3,200 head. A moderate number of bison from outside sources will be added during the build-up period for genetic improvement.

Bison Unit

The Christina Adams herd was introduced into a 5,000-acre (2,023 hectares) pasture, the bison unit. Twelve miles (19 kilometres) of bison proof perimeter fence was constructed to contain the herd; there are no internal fences within the 5,000 acres. As the herd increases in number, the size of the bison unit will be systematically enlarged to ultimately occupy the entire area of the Preserve.

Although primarily tall grass prairie, the bison unit encompasses a significant amount of post and blackjack oak motts

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and riparian

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corridor forests. Unit management requires prescribed burns of grassland areas in spring, summer, and fall to create a shifting patchwork landscape. Average burn frequency is 3 to 5 years. Fire interval is generally 3 years. No fixed burn units exist; rather, burn units are selected randomly from areas that contain the highest fuel loads, with some managerial discretion.

Bison Herd Management

All Conservancy bison herds are managed under the same guidlines. A minimal management approach is used, allowing the bison to behave as naturally as possible. No supplemental feeding is practised. Bison receive standing forage year-round, water, and free-choice salt with trace minerals if this is lacking naturally in their management unit. Stocking rates are moderate to light when compared with typical annual cattle rates. Bulls are not removed from the herd after the breeding season, and calves are not artificially weaned. A few fall calves can be expected each year but most are born in spring.

Every autumn the herd is rounded up, handled through a specially designed corral system, culled, and vaccinated. Because wolves and bears, the historic predators, are no longer present on the prairie, low-vigor and old adults and calves are culled to simulate the effect of predation. Culled animals are separated from the herd and sold live to private bison ranchers. Sale of culled bison is an important source of operating funds for the Preserve. Cows are usually culled when 10 to 12 years old, and bulls when 6 to 7 years old. This early culling of bulls is also a practical management technique to reduce containment problems. Once the herd size of 3,200 animals is reached, approximately 1,100 bison will be sold each year.

The Tall Grass Prairie Preserve has a strict brucellosis and tuberculosis prevention program, as do all Conservancy preserves with bison. Any acquired animals are certified as free from disease before being transported to the Preserve, and all animals sold from the Preserve are tested before leaving. Heifer calves are vaccinated against brucellosis. Animals are also treated for parasites and other diseases as necessary.

The Nature Conservancy does not see itself playing a major role in the efforts to maintain the genetic diversity of bison, the Conservancy is committed to maintaining adequate genetic diversity within and among its herds. It is not Conservancy intent to be in the bison ranching business, instead objective is to create an evolutionally viable, process-driven landscape in which bison play an important role.

Bison are not a rare or endangered species and, therefore, are not a target of conservation effort by the Conservancy. What the Conservancy is doing is restoring an important cog in the ecological machinery.

Cattle

After leaving the Preserve ungrazed during 1991 and 1992, The Nature Conservancy introduced controlled cattle grazing in 1993. Area used for cattle grazing will decrease gradually as the bison range increases. Eventually, cattle grazing will be restricted to an area of about 1,000 acres (405 hectares), which will be kept as a control plot, to allow comparative studies of eating habits and grazing preferences of cattle and bison.

At present, winter grazing is allowed during the dormant season, through lease arrangement only. Grazing like this permits a gradual increase in the size of the cattle herd over these winter and spring months in preparation for the summer grazing period.

Summer grazing period is 90 days, approximately, from 15 April through 15 July. All cattle are removed by 20 July. Regeneration of the prairie is permitted for the second half of the growing season, without grazing pressure. Commonly referred to as high intensity short duration grazing, this system mimics grazing by bison that is relatively high pressure for a short period of time; it is a system proven to be an effective prairie management technique. High intensity short duration stocking will be used with cattle until the bison herd reaches the desired size.

Cattle grazing leases provide the influence needed by the prairie and generates operating funds for the Preserve. Leases consist of short duration, high intensity grazing that can be combined with rotational grazing systems to mimic the effects of bison grazing pressure. Preserve science staff determine the season of use, stocking rates, and rotation schedule for all leases. Leases are selected by a process of sealed bid.

Acknowledgements

This article is a lightly edited reproduction of source material provided to docents of the Tall Grass Prairie Preserve by The Nature Conservancy for dissemination to the public.