American Bison

Characteristics

This animal is in the same family as cattle, yet its appearance sets it apart. Bison are the largest terrestrial mammals in the western hemisphere. Large bodied, wide triangular head, with brown hooves with a hunchback appearance and horns are signature characteristics of this species.

Species Specifics

American Bison are divided into two subspecies, plains bison (B. b. bison) and woods bison (B. b. athabascae) that are inhabitants of the woodlands of northern Canada and Alaska. Plains bison are smaller and lighter in color than the woods bison.

Physical Characteristics

Bison are usually slow moving, but can run up to speeds of 37 mph when chased. They have a strong sense of smell (aiding in predator detection) and can hear and see well. They are also strong swimmers. Bison are better able to maximize nutrition in areas with poor forage and have lower cholesterol, fat, and calories in their meat than cattle.

Ecology

Habitat

Grassland, aspen parkland, coniferous forests

Distribution

771 miles for adult females and between 439-660 miles for males.

Diet

Herbivorous; 15-18 lbs. of greens per day. Can meet water requirements by eating snow, but prefer to drink from open water.

Ecological Web

Where bison have been studied, grazed areas have a 36-85% higher production of grass than ungrazed areas, partly stimulated by the high mineral content of bison feces and urine, which contain 90% of the phosphorus and 65-95% of the nitrogen from ingested foods. Predators: Gray wolves, grizzly bears and humans.

Activity and Behavior

Activity Pattern

Bison graze for 9-11 hours each day, resting, ruminating, or moving for the remainder. They generally stay in one area for several days then travel several miles to a new area. They can move during the night or day. They migrate with changing seasons; winter foraging areas occur more often in sheltered meadows and in riparian zones. Most herds today can no longer make long migrations due to fences.

Behavior

During storms, they will face into the wind and rain and endure them. Regardless of age and sex, they roll in dust baths and mud wallows which help protect their skin against mud and help dislodge old fur. They will also rub on trees, boulders, and other objects to dislodge old fur.

Social Behavior

Herd sizes are generally 20-60 animals and communicate via vocalizations and posture, including tail placement. Older bulls can move alone or can form bachelor herds. Males will exhibit threat displays and fight year round; most frequently before and during rut. Females will threaten and charge when protecting their calves. A study in Alberta found that 73% of threat displays did not get physical. If bison do fight, males can collide at full gallop and wrestle with horns locked. Horns can break ribs and puncture organs.

Reproductive Behavior

Females go into estrus about every 3 weeks for only 9-28 hours. Males exhibit the flehmen response, tasting the female's urine to establish if she is in estrus.

Offspring

1; can weigh up to 66 lbs. at birth and generally are not weaned until they are 8-12 months old.

Conservation

Status

Listed as Near Threatened by the IUCN; One subspecies (B. b. athabascae) listed in Appendix II of CITES and Threatened under Endangered Species Act. Population Trend: Stable, Current herds occupy less than 1% of their historic range.The total number of mature individuals in wild free-ranging and semi-free-ranging populations is estimated to be approximately 11,250 and most bison are on private lands.

Historical

American Bison, also known as American Buffalo, once roamed the grasslands of North American in large herds. They are the largest land animal on the continent weighing between 1000-2000 lbs. in males and 800-1200 lbs. in females. Bison were nearly wiped out in American history. In the 19th century Westward expansion, Bison neared extinction due to slaughter and bovine diseases from domestic cattle. They declined from 30-60 million free ranging to around 1000 in 1906. A small original heritage wild herd was taken to Canada and remained established at Elk Island Park. Crossbreeding with cattle (thought to create healthier meat and more resilient animals) has increased the population, but has also polluted most remaining wild herds of bison, and increased exposure to deadly cattle diseases. Habitat loss also results in little space for Bison to develop large, genetically diverse herds. Today there are around 500,000 bison on private lands and 30,000 on public lands, but only about 15,000 are considered wild, free-range bison not primarily confined by fencing. Current herds occupy only 1% of their historic range. The Northern Tribes Buffalo Treaty was signed in 2014 to enable partnership to restore wild buffalo to the plains. President Obama signed the National Bison Legacy Act into law in 2016, making the American bison the national mammal of the United States.

Current Threats

Our Role

Iinnii Initiative: Oakland Zoo partners with WCS and the Iinnii Initiative in Montana to restore a wild herd of American bison to their native territory. The Zoo raises young bison for yearly release in Montana, in the care of the Blackfeet Nation. This program adds genetic diversity to the heritage herd and bring back a culture that will enhance the well-being of the bison, the local people and the nature around them. Oakland Zoo is developing eco-travel programs to Montana, to study bison with the Blackfeet Nation Communities, an Economic Benefit program to sell Blackfeet Nation artisan goods at our gift shop, production of Blackfeet Nation Bison ceremonies and an annual National Bison Day in November, and creation of a Teen Cultural Exchange with Oakland Zoo and Blackfeet Nation youth. Oakland Zoo is also working with the the Zoo Parks Partnership (ZPP) to enhance our relationship with Glacier National Park and benefit bison and other animals in this shared habitat.