American Bison
Near Threatened
Grasslands
North Americ
Diurnal
Herbivorous
California Trail
Characteristics
Bison are the largest terrestrial land mammal in the Western Hemisphere. With a large body, humped shoulders, and a triangular face with horns, these bulky mammals can get as large as a literal ton, 2,000 pounds. Males on average weigh 1,800 pounds and stand 6 feet tall at the shoulder. Females weigh 1,200 pounds and stand 5 feet tall. Don’t let their size fool you, even though they are usually slow movers, they can still run up to 37 mph when needed, and are strong swimmers.
As is common among many bovine species, both males and females have horns. American bison have two black horns that curve upward and inward from the crown of the head which end in sharp tips. They have a distinctive shoulder hump and a huge head. Their fur is brown and varies in length across the body. Their head, neck, shoulders, and forelegs have a very thick, long, and shaggy coat. The rest of their body has much shorter hair. During the spring, bison shed their coats for the summer.
Habitat & Ecology
As their name suggests, American bison live in North America. Currently, populations range from as far north as Alaska, all the way down to Arizona. Historically, however, bison were widespread across the continent and primarily found in grasslands and prairies. As their population became threatened and started decreasing, their range became fragmented. Now, thanks to conservation efforts, bison have been reestablished in many regions. Unfortunately, they continue to be substantially fragmented. Bison can now be found at all elevations within national parks and reserves.
American bison have incredible impacts on the areas they graze. Studies tell us that there is a 35-85% increase in the production of grass in areas that bison graze on. This growth stimulation is from the high mineral content of bison feces and urine. Their waste contains 90% phosphorus and 65-95% nitrogen, acting as a natural fertilizer.
Diet
American bison are herbivores, meaning they only eat vegetation. They spend up to 12 hours a day grazing on grasses, flowering plants, and lichens. They can consume up to 12-18 pounds of food per day. While bison prefer open water to drink from, they can also get their water requirements from snow. With their massive head and shoulders, bison can shovel snow out of their way to find food during the winter.
Bison are ruminants, just like cows and goats, and have a four-chambered stomach. This means that after swallowing their food the first time, they regurgitate it after a while to chew it some more before swallowing again. This process allows them to digest complex vegetation with a high cellulose content.
Behavior & Reproduction
Bison are diurnal creatures, they spend 9-12 hours each day grazing, and will rest, ruminate, or travel for the remainder. They are social animals that live in herds of 20-60 individuals. These herds largely consist of females, or cows, and their young, as well as immature bulls. Older bulls are often solitary and will enter the groups to rut or mate.
Bison will generally stay in one area for several days before traveling several miles to find a new place to settle. Bison will roll in dust baths and mud wallows to help protect their skin against bug bites, shed fur, and as a cooling mechanism. American bison have an excellent sense of smell and hearing. Their sight on the other hand, is incredibly poor. They are very near sighted, which helps them distinguish different types of plants. To communicate, bison will use different vocalizations and posturing.
American bison can go into estrus at any point during the year, but it is generally centered around summer when food is plentiful and the mother can support herself and nursing a baby. Estrus only lasts 9-28 hours and will cycle every 3 weeks. Their gestation is just like other cattle, ranging from 9-10 months, almost a whole year! When a baby bison is born, they weigh an average of 66 pounds. They will nurse until mom doesn’t let them anymore, which can be as soon as 4 months, but generally is between 8-12 months. Male bison, or bulls, don’t mature until they are 6 years of age, but females can reach maturity at 3 years of age. Mature bulls may fight each other over the cows. They attempt to restrict access to a small group of females that only they will mate with. Males do not provide any parental care.
Wild: 20 years, Protected Care: 40 years
June-September
1
1 year
Conservation
American bison historically have had a lot of significance in the United States. They were deeply intertwined with the economy of many Native American groups. Many of the paths created by bison through mountains were then used by highway crew to map routes in the western United States. Additionally, bison were, and still are, used for meat. It was therefore a huge blow when their population started to decline. Pre-1800, there are estimates of anywhere between 30-100 million individuals roaming the continent. During the Western Expansion period in the early 1800’s the bison population declined significantly primarily from the unregulated and extreme hunting efforts by settlers. By the 1890s, fewer than 1,000 individuals remained in the wild. They are currently listed as Near Threatened by the IUCN.
However, American bison are making a comeback! Currently, conservation herds comprise around 30,000 bison. These conservation herds have allowed for the reintroduction of American bison to several of their old stomping grounds.
Fascinating Facts
- The word buffalo is derived from the French “bœuf,” a name given to bison when French fur trappers working in the US in the early 1600s saw the animals. The word bœuf came from what the French knew as true buffalo, animals living in Africa and Asia. In the United States, however, it is acceptable to call American Bison both “bison” and “buffalo” because of their history.
- 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.
- Celebrate National Bison Day every year on the first Saturday of November!
About Our Animals
The Oakland Zoo is proud to have a conservation herd of American bison. We work together with the Iinii initiative in Montana and Alberta, Canada to restore bison to their native territory. In 2018, we started with a herd of 14 females. In 2019, two bulls from Yellowstone came to join the herd and add genetic diversity. Since then, our herd has raised 32 calves, and 38 of our bison have returned back to their ancestral home range. Our herd has over 13 acres to wander and graze on, but can often be spotted from the Gondola or their viewing platform on the California Trail.
Our Role
Oakland Zoo partners with the Wildlife Conservation Society (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.
