American Bison (Bison bison) Fact Sheet: Behavior & Ecology

• Active during day (diurnal). Intermittent grazing and ruminating throughout a day, led by a cow.
• Move about 3 km (1.9 mi) per day, but varies according to habitats, presence of biting insects, water. (Meagher 1986)
• Several times a day in summer, engage in wallowing to put dirt and dust into their hair (keep insects off the skin, protect against heat) (Lott 2002)

• Plains Bison are non-territorial and are nomadic
• Plains bison living in small herds may be non-migratory with fidelity to a home range (Guthrie 1990)
• When free-ranging, are seasonally migratory, moving to lower or more southerly habitats in winter. (Nowak 1999)
• Distances traveled between winter and summer territories may be up to 40 km (25 mi) in mountainous habitats and 240 km (149 mi) in boreal-forest parkland habitats. (Meagher 1986)

General

• Bison are gregarious, forming fluid groups of females with calves, young males up to 2 or 3 and possibly a few older males.
• Breeding age males play no role in calf raising and normally do not mix with the cow and calf groups
• Males live alone or in small herds of males.
• Groups of adult females with their young in one study of free-ranging individuals in Montana averaged 57 individuals. (Nowak 1990)

Dominance hierarchies

• Dominance in males is linear
  • Top bull dominates over all of group
  • Bull with 2nd most dominant role dominates over all the group except for the top bull.
  • This pattern continues down the ranking, so that subordinate males only rarely challenge the order
• Dominant bulls have higher cortisol levels, indicating that their social status makes for significant physiological stress during rut. (Mooring et al 2006)
• Dominance strongly correlates with age and weight in bachelor groups (Roden et al 2004)

•  Bison are nomadic, may move several miles a day while feeding. (Lott 2002)
  • Amount of movement influenced by quality of habitat's plants, presence of biting insects, amount of water available (Meagher 1986)
  • Bison herds moved 3.2 km/day in a montane valley to 2.8 km/day in coastal scrub-grassland (Meagher 1986)
• In shrub-steppe habitats of Southern Utah, herds remained in one area about 2 days. (Van Vuren 1983)

Aggression

• About 5 to 10 percent of bulls' challenges lead to fights. (Lott 2002)
• When bulls threaten, they may bellow, stamp feet and snort, approach each other with tails high (Lott 2002)
• When fighting, bulls run together, clash heads, then push upwards with heads held low. (Lott 2002; Guthrie 1990)
  • Cattle fight in a different way, by hooking with horns, then pushing. (Guthrie 1990)
  • Relatively short horns of B. b. bison allow a bull to slip to the side after head clashing and gore an opponent; such wounds are frequent (Guthrie 1990)
• Bulls may approach closely, heads turned sideways, then nod the head up and down until one may attack or submit before an attack; called a "nod threat" (Lott 2002)
• Turning the head sideways when two bulls threaten as they face each other, indicates submission; then the contest is over and the winner does not attack. (Lott 2002

Visual communication

• Broadside threat posture displays give best view of overall large body size; may intimidate opponents into submission (Lott 2002)

Vocalizations

•  Bulls may bellow when threatening each other.
  • This sound has been compared to a lion's roar and can be heard up to 5 km (3 mi) away. (Meagher 1986) (Buchholtz & Sambraus 1990)

Olfaction/Scent Marking

• Males that are competing with each other may wallow, then urinate in the wallow and roll in the urine before resuming their challenges (Lott 2002)
• Females have also been observed urinating into wallows and rubbing their necks on the soil. (McMillan 2000)
• Bulls use a lip curl and tongue (flehmen) to transfer cow's hormone-packed urine to a receptor organ in the roof of his mouth. (Lott 2002)

• Gaits include walking, trotting, galloping, bounding. (McHugh 1958)
• Can run up to 60 km/hr (37 mph)
• Known to leap over barbed wire fences; surprising agility for animal its size
• Good swimmers; can swim rivers at least 1 km (.6 mi) wide. (Meagher 1986)

•  Bison grazing in Flint Hills of Kansas increased abundance of Upland Sandpipers, Grasshopper Sparrows and together with the effects of recent prescribed burnings, lowered numbers of Dickcissel. (Powell 2006)
• Human prescribed burning plus intense bison grazing may lower numbers of four grass-dependent species of sparrows and Eastern Meadowlarks, and shrub-dependent Bell's Vireos. (Powell 2006)
  • After grazing by bison, there are fewer plants, but more species; grazing increases diversity of grassland species, as does a fire. (Lott 2003) (Powell 2006)
• Grazing bison keep grasses short, which promotes prairie dog colony survival; prairie dogs don't live in areas with tall grass where they can not see approaching predators. (Lott 2003)
• Bison are attracted to bare dirt for dusting fur in prairie dog towns.
• Brown-headed cowbirds (Molothrus ater) forage on insects disturbed by grazing bison.
• Sedges and rushes (water loving plants) grow in compacted bison wallows that can hold extra rainfall. (Lott 2003)
• Many other ungulates co-exist with bison using different foraging techniques and plant preferences
• Native Americans living in bison habitats depended on bison for much of their subsistence.
• Bison fertilize the grasslands.

Play

• Play behavior peaked at dusk for young bison. (McHugh 1958)
• Young bison play more than adults. (McHugh 1958)
• Young often engage in wallowing during play (McHugh 1958)
• Juveniles chase, play-mount, butt heads (but don't lower heads when doing so)

The winter coats of American bison—composed of wooly under-hairs and tougher, water-resistant top hairs—make them superbly adapted to harsh weather conditions.These heat-retaining hairs are molted during warmer seasons.

Historically, their coats were valued by native peoples and settlers for their thermal qualities.

Image location: Yellowstone National Park, Montana.

Image credit: © Carra, Lexington, Kentucky. Made publically available via Wikimedia Creative Commons license 2.0.

Guthrie (1990)
Lott (2002)
McHugh (1958)
McMillan (2000)
Meagher (1973, 1986)
Mooring (2006)
Nowak (1990)
Powell (2006)
Roden et al. (2004)
Van Vuren (1983)