Geography of American Bison

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On May 9, 2016, the American Bison (Bison bison) was named the national mammal of the United States of America.

Learn some interesting geography facts about the American Bison which once roamed North America in vast herds.

What is a Bison?

The bison is North America’s largest mammal. Bison are herbivores and graze heavily on grass species and sedges found in mixed-grass prairies.

Males, known as bulls, can weigh as much as 2,000 pounds and reach a height of six feet. Females, known as cows, weigh as much as 1,000 pounds and range between 4-5 feet in height. Bison travel in herds.

Despite their size, bison are remarkable quick and can run up to 35 miles per hour and pivot quickly to avoid predators such as grizzly bears and wolves.

A bison cow with her calf. Photo: Jesse Achtenberg, U.S. Fish and Wildlife Service. Public domain
A bison cow with her calf. Photo: Jesse Achtenberg, U.S. Fish and Wildlife Service. Public domain

Prehistoric Range

The historic range of the American Bison spanned from Alaska down into Mexico, covering almost two-third of the continent of North America. This tract of rich grassland around 9,000 B.C. was known as the Great Bison Belt. The short grasses provide year-round nutrition for bisons, supporting as many as 30-40 million of the large mammals at the peak of their population.

Researchers estimate that the original bison range was 9.4 million square kilometers in area and cover 22 major biomes ranging from the arctic lowland taiga forests of Alaska to the western grasslands of Mexico.

Changes with European Settlers

The arrival of European settlers dramatically reduced both the geographic range and population numbers of the bison. As settlers moved west in the 1800s, hunting, competition with cattle for prairie grass, and changes to the landscape decimated bison populations.

The transcontinental railroad was built through the center of the bison range between 1867 and 1883, dividing the population in half. By 1883, the bison population was down to less than 1,000 individuals.

Map illustrating the extermination of the American bison, 1889 by William Temple Hornaday.
Map illustrating the extermination of the American bison, 1889 by William Temple Hornaday. Map: Library of Congress, public domain.

Reestablishing Bison Populations

In 1905, the  American Bison Society was founded by conservationists including Theodore Roosevelt and William Hornaday, the first director of the Brooklyn Zoo, to save the nearly extinct bison.

In 1913, the American Bison Society donated 14 bison to Wind Cave National Park. The donation consisted of seven males and seven females.

Current Range

The bison today is restricted to small and separate populations. The federal government manages about 17 herds found west of the Mississippi in 12 states.

Notable publicly owned bison herds are: Yellowstone Park (2,300-5,500 bison), Custer State Park, South Dakota (1,300 bison), the Henry Mountains bison herd in south-central Utah (300 to 500 animals), the herd at Wind Cave National Park in South Dakota (350 bison), and Antelope Island (550 and 700 bison).

Other bison populations can be found on private property or with state and local agencies. For example, Golden Gate Park in San Francisco has a bison paddock with the park grounds.

Today about 30,000 bison are managed for conservation and another 400,000 are held as livestock in North America.

Largest Bison Population on Public Lands

Yellowstone National Park is the only place in North America where Bison have continuously roamed since prehistoric times. These bison are free on mixed genes from cattle, making them some of the only pure bison.

Bison grazing along a meandering stream, Rose Creek in Lamar Valley.  Photo: Neal Herbert/NPS, public domain.
Bison grazing along a meandering stream, Rose Creek in Lamar Valley. Photo: Neal Herbert/NPS, public domain.

Yellowstone’s bison population is the largest on public lands. The number of bison in Yellowstone ranges between 2,300 to 5,500 animals in two subpopulations.

Herbivores, these bison graze freely across the enormous expanse of Yellowstone National Park and several adjacent areas of Montana. The northern herd is found in the the Lamar Valley and the nearby plateaus. The central herd is located in Hayden Valley

When releasing new bison into Yellowstone, researchers use satellite image to analyze snow patterns. Melting snowpacks influence the migration of bison – deep snow in Yellowstone drives bison to move towards lower elevations and sometimes beyond the park boundaries.

By mapping snowmelt through the use of satellite imagery, park rangers can time the release to reduce the likelihood of bison moving out of Yellowstone where they can come into conflict with local ranchers.

The migratory pattern of the bison herd in Yellowstone National Park is depicted in this map made from NASA Landsat satellite data.
The migratory pattern of the bison herd in Yellowstone National Park is depicted in this map made from NASA Landsat satellite data. Map: NASA.

How Much do Bison Move?

Between summer and winter ranges, free-range bison can travel up to 70 miles away between their summer and winter ranges. Most bison will move roughly 1,000 miles a year by constantly moving back and forth to the same regions.

Six starlings perched on the back of a bison.
Birds like these starlings will perch on the backs of bison to hunt for insects that have been stirred by the by grazing movements of bison. Photo: Kim Acker/NPS, public domain.

Starting in winter, bison will move towards their summer ranges, following a “green wave” of emerging vegetation. Related: Do Bison Influence the Spring Season?

Are Bison Buffalo?

Although a misnomer, early explorers referred to the bison as “buffalo” (taken from the French le boeuf) and the name stuck. While they make look similar, old world buffalo don’t have the large shoulder hump found on American Bison.

The English language is full of quirks. From eight different ways to pronounce words ending in “ough” to victual being pronounced as “vittel“, the language is full of eccentricities.

Sentences employing the same word over and over are one of the more head-scratching oddities.  These are grammatically correct sentences that use just one word repeatedly.  Once example is:

Buffalo buffalo Buffalo buffalo buffalo buffalo Buffalo buffalo.

The repetition takes advantage of a mix of three distinct meanings while combining verbs and nouns that are all spelled buffalo.  The uppercase Buffalo refers to a proper noun, such as the New York city of Buffalo.  The lower case buffalo has two distinct meanings.  Buffalo is a noun that refers to a large wild ox with large horns (such as the water buffalo).  A buffalo is also known as a bison in North America.  Buffalo is also a verb, meaning to intimidate or baffle.

References

15 facts about our national mammal: The American Bison. (2016, May 9). U.S. Department of the Interior. https://www.doi.gov/blog/15-facts-about-our-national-mammal-american-bison

Bison. (2021, June 29). NPS.gov – Yellowstone National Park. https://www.nps.gov/yell/learn/nature/bison.htm

Bison bellows: Back home on the range (U.S. National Park Service). (2017, November 6). NPS.gov (U.S. National Park Service). https://www.nps.gov/articles/bison-bellows-1-7-16.htm

Bison bellows: Bison east of the Mississippi (U.S. National Park Service). (2017, November 6). NPS.gov (U.S. National Park Service). https://www.nps.gov/articles/bison-bellows-9-16-16.htm

NASA studies snow to save Bison at Yellowstone National Park. (2006, November 2). NASA. https://www.nasa.gov/vision/earth/lookingatearth/yellowstone_bison.html

The return of the Bison. (2019, February 9). NPS.gov (U.S. National Park Service). https://www.nps.gov/wica/learn/historyculture/the-return-of-the-bison.htm

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