The Great Plains bison stands as an enduring symbol of North America’s natural heritage. These majestic mammals once roamed vast stretches of grasslands, shaping the landscape with their immense numbers and movements. Their historical presence across the continent highlights their deep connection to the North American ecosystem. The bison represents a remarkable story of resilience and ecological significance.
Distinctive Features and Social Life
Great Plains bison are characterized by their formidable size, making them the largest terrestrial animals in North America. Adult males can reach heights of 5.5 to 6.5 feet at the hump and measure between 9 to 12.5 feet in length, weighing 1,800 to 2,400 pounds. Females are smaller, typically 7 to 10 feet long and 5 feet high at the hump, with a weight of 1,800 to 2,400 pounds. Their distinct physical traits include a prominent hump over their front shoulders, a long, shaggy dark-brown coat, and short, backward-arching horns.
Bison are primarily grazers, eating grasses and sedges found in prairie environments. Their daily routine involves two-hour periods of grazing, resting, and cud-chewing, after which a group moves to a new grazing area. While grasses are their primary food source, their diet can shift seasonally to include woody shrubs in spring and fall, and legumes during summer. This adaptability is influenced by plant availability.
Bison organize into groups based on sex, age, season, and habitat. Older bulls often live solitary lives, while females with young form smaller groups for most of the year. These smaller bands may then converge into larger herds during spring or fall. Mature males also form their own groups, which can include up to 30 individuals.
Breeding occurs from late June through September, with dominant males protecting selected females. A female’s gestation period lasts 285 to 300 days, resulting in the birth of a single calf. Calves, born with a yellow-red coat, are able to keep up with the herd within a few days and remain with their mothers until the following spring. Bison reach sexual maturity between two and three years of age and can live up to 25 years.
Their Role in Prairie Ecosystems
Great Plains bison are ecosystem engineers, shaping the health and diversity of prairie habitats. Their grazing patterns directly influence plant communities by selectively consuming certain species, which can promote the growth of others and increase overall plant diversity. This selective grazing helps maintain the dynamic balance of grassland ecosystems.
Beyond grazing, their movements and behaviors create varied microhabitats across the landscape. As they travel, bison form distinct trails, and their wallowing behavior—rolling in dust or mud—creates depressions in the ground. These wallows collect water, providing habitats for various species, while also exposing mineral-rich soils that benefit various plant species. Such activities contribute to landscape heterogeneity, fostering a greater variety of species and ecological niches.
The historical migratory patterns of bison also had a significant impact on grassland heterogeneity. Their large-scale movements across vast landscapes prevented overgrazing in any single area and distributed nutrients through their waste. These movements help maintain the open, expansive nature of the prairies, preventing the encroachment of woody vegetation and supporting the diverse array of grassland species that co-evolved with them.
From Near Extinction to Recovery
The Great Plains bison population experienced a severe decline in the 19th century, driven largely by extensive hunting. Once numbering in the tens of millions, their population plummeted to fewer than 1,000 individuals by 1900. This dramatic reduction pushed the species to the brink of extinction. This period marked a significant loss of a species that had been a dominant force in North American ecosystems for millennia.
Conservation efforts began in the late 19th and early 20th centuries to protect the remaining bison. These efforts included the establishment of protected herds in national parks and reserves. Organizations and individuals worked to gather the last remaining bison and establish breeding programs. These initial steps were fundamental in preventing the complete disappearance of the species.
Today, the Great Plains bison population has seen a remarkable recovery, though their numbers are still a fraction of their historical abundance. There are 20,500 individuals in 62 wild conservation herds. However, more than three-quarters of these herds are considered too small to be “minimally viable,” meaning they may lack sufficient genetic diversity or resilience to thrive long-term. Only one herd currently exceeds 2,000 bison, and only 14 herds have more than 400 individuals. While significant progress has been made, ongoing management and conservation initiatives remain important to ensure the continued growth and genetic health of these iconic animals.