Custer State Park in the Black Hills of South Dakota is home to one of the largest publicly owned herds of American bison. This herd is a powerful symbol of wildlife conservation, tracing its origins back to 36 animals purchased in 1914. These majestic animals roam freely across the park’s expansive 71,000 acres, drawing visitors from around the world. Managing this population is a complex, year-round effort that balances ecological sustainability with historical preservation.
The Current Buffalo Population Estimate
The number of buffalo is dynamic, fluctuating significantly throughout the year. Park management maintains a specific target herd size to ensure the health of the animals and the environment. Before the annual management activities, the herd typically numbers between 1,300 and 1,500 animals. This count includes calves born that year, reflecting the natural growth rate.
After management actions are complete, the park aims to “overwinter” a population closer to its ecological capacity. For example, the goal was recently to retain a post-management population of around 975 bison. This targeted reduction prevents the animals from outgrowing available resources. The retained number acts as the breeding stock for the following year.
Ecological Management and Carrying Capacity
The decision to maintain a herd under 1,000 animals is tied to carrying capacity—the maximum population size an environment can sustain indefinitely. Custer State Park’s grasslands can only support a certain density of large grazing animals before the habitat degrades. Ecologists estimate the park can optimally sustain around 1,000 bison.
Allowing the herd to grow beyond this capacity would lead to severe overgrazing, damaging the ecosystem. Overgrazing removes plant cover, which causes soil erosion and reduces biodiversity. This ecological stress would harm other species and increase disease risk within the bison herd itself. By controlling the numbers, park officials ensure sufficient forage and water to sustain the animals through the winter months. This approach preserves the diverse prairie ecosystem for all wildlife.
The Role of the Annual Buffalo Roundup
The mechanism used to achieve carrying capacity goals is the annual Buffalo Roundup, an essential management event held each September. While it draws thousands of spectators, it is the primary tool for herd control and health assessment. Cowboys and cowgirls on horseback drive the entire herd across the range into corrals.
Once contained, park staff begin the intensive process of sorting, testing, and treating the animals. Calves are vaccinated, and all animals undergo health checks. Officials then determine which animals will be retained for breeding stock and which will be classified as surplus.
The excess animals, typically numbering between 400 and 500 each year, are separated and sold at a public auction. This sale reduces the herd size to the target overwintering number. The revenue generated supports the park’s conservation efforts, and the genetics often contribute to the improvement of other bison herds across the nation.