Bison Facts

A herd of fifty bison in a meadow surrounded by a mixed conifer forest.
Bison herd in Little Park meadows on the North Rim of Grand Canyon National Park. (S. Ciarrachi, 2016)

The North American Bison (Bison bison) was designated the official National Mammal of the United States on May 9, 2016. The Plains Bison (Bison bison bison) once roamed the majority of the open grasslands across the United States to northern Mexico. Their historically massive herds are now significantly smaller and mostly found in geographically isolated populations within parks and preserves. A herd of bison from House Rock Valley Wildlife Area has expanded their range inside of Grand Canyon National Park boundaries, exponentially increasing from one confirmed sighting in 1996 to a current estimated population size of 400 to 600 individuals.

Identification

  • Largest North American mammal: males (bulls) weigh up to 2,000 pounds and can stand up to 6 feet tall, females (cows) weigh up to 1,200 pounds and can stand between 4 to 5 feet.
  • Bison have a massive head with a large shoulder hump. Their thick dark-brown fur tends to be longer around their chin and forelegs. Bison obtain a wooly winter coat and molt late winter-early spring. Both sexes possess curved horns that point upward and are larger on males.
  • Calves are born at 25-40 pounds with reddish-tan hair, giving them the common name “red dogs”. Their shoulder humps begin to protrude at around 2 months of age.
Young bison calf on a grassy area near spring, watching a bird.
"Red dog" at Basin Springs on the North Rim of Grand Canyon National Park admiring a bird, 2017. (NPS camera trap photo)

Behavior

  • Wild bison can live up to 20 years.
  • Bison are grazers, they feed primarily on grasses and possess a ruminant digestive system.
  • Diurnal animals, bison roam an average of 2 miles daily. Cows and calves roam together in larger herds while bulls tend to roam either alone or with just a few other males.
  • Herds interact by grunting and a bull's bellow can be heard up to 3 miles away.
  • Bison are massive but agile mammals that can run a speed of up to 35 mph, leap over fences, and swim rivers at least .6mi wide. When fighting, males will run towards each other and clash heads using their matted fur as cushion. Because their shoulder hump is primarily muscle, they regularly use their heads to plow through snow during winter seasons.
  • Bison wallow as a way to dust themselves in order to keep insects away. Urinating in wallows is used by bulls for scent-marking during competition and by cows for hormone transferal.
  • During mating season (June-September), bulls reunite with herds of cows and will tend fertile females. Gestation lasts 285 days and calves will nurse 7 to 9 months, becoming independent at around 1 year of age.
  • Both sexes become sexually mature between 2 and 4 years of age. Physical maturity is reached at 3 years old for females and 6 years old for males.
Herd of forty bison surrounding a pond. A calf nursing on a cow in the foreground, while two young males play fight behind them.
A bison herd surrounding Kanabownits Pond on the North Rim of Grand Canyon National Park, 2017. (NPS camera trap photo)

Habitat

  • Historically, Bison bison roamed the grasslands and prairies of North America, ranging from Eastern Alaska through western Canada and south into Northern Mexico.
  • A bison herd brought to House Rock Valley in the early 1900’s now roams inside Grand Canyon’s North Rim boundaries and the surrounding National Forest.
  • In Grand Canyon National Park, bison roam in the open meadows and dense forests of the North Rim congregating around natural water sources.
A large bull wallowing in a grassymeadow of a lush, mixed conifer forest. His wallowing kicks up a cloud of dust.
Bull wallowing near Big Spring on the North Rim of Grand Canyon national Park, 2017. (NPS camera trap photo)

Prepared by Desiree Espericueta, Wildlife Technician, Grand Canyon National Park (February 2018).