THE ANIMAL FILES

American bison

Bison bison

A dust bath can leave a small hollow with a lasting footprint.

American bison graze, move between feeding areas and roll in shallow wallows. Their broad front bodies and changing coats are conspicuous, but the ground disturbed by their behaviour also becomes part of a grassland’s physical structure.[1]

Follow the evidence ↓
American bison
Image: Jack Dykinga · Commons · Public domain
Food
Primarily grasses and sedges[1]
Horns
Both sexes have short curved horns[1]
Wallow
A shallow soil depression used wet or dry[1]

A different coat for winter

Bison carry a long, shaggy winter coat that is heavier and darker than the summer covering. Males are generally larger than females, but both sexes have horns. Young calves begin with lighter colouring before acquiring the mature appearance.[1]

Grazing follows a changing resource map

Bison move among feeding sites, and some herds make seasonal or elevational movements. Vegetation change, water and landscape constraints influence the areas used. Grasses and sedges dominate the diet, while other plants may become more important under different conditions.[1]

Rolling alters the soil surface

Bison use shallow depressions for wet or dry wallowing and coat themselves in mud or dust. Researchers have proposed several functions, including grooming and relief from irritation. The physical disturbance is clear even where the relative importance of each proposed benefit depends on context.[1]

A COMMON MIX-UP

Does a mud-covered bison have one proven reason for every wallow?

No. Several functions have been proposed, and wet and dry wallows both occur. Describing the observed rolling separately from its possible benefits avoids presenting a list of hypotheses as a single settled explanation.[1]

TRY A LITTLE REASONING

What might remain after a bison leaves a wallow?

Reveal the explanation

A depression and disturbed soil persist beyond the animal’s visit. These physical changes help explain why bison behaviour can influence the pattern of vegetation and small habitats across a prairie.[1]

Sources & editorial notes

Adapted and translated from the cited Wikipedia revisions, with source-linked reasoning. Image credit and licence are listed separately above.

Adapted and translated from Wikipedia contributors; exact revisions are linked below. CC BY-SA 4.0

  1. Wikipedia contributors — American bison (fixed revision; adapted and translated)
  2. NCBI Taxonomy — Bison bison (identity and classification)

Last fact check:

One discovery leads to another

YakThe long coat is only the visible layer of a high-altitude animal.Bos grunniens ↗Water buffaloWater and mud help a buffalo manage heat.Bubalus bubalis ↗Domestic goatA browsing adult begins life on a very different diet.Capra hircus ↗