Like domestic cattle, bison are grazers. However, they prefer young, tender grasses and eat few forbs (such as wildflowers). They walk along biting off mouthfuls of grass, barely chewing it before swallowing. Cud-chewing occurs later in the day when the hastily swallowed grass is brought up, portion by portion, to be broken down more completely in a second chewing.
Feeding mainly in early morning and the late afternoon, bison normally rest and chew their cud during mid-day and at night. Research at the preserve has found that not less than 99% of a bison's diet is grasses and sedges. The bison's rubbing on young trees helped prevent trees from invading the prairie. When necessary, bison will travel a long way to find water; however they can go for long periods without it.
Wallowing is practiced by both sexes and all age classes. Wallows are usually in dry areas, but wet areas may be used. This behavior seems to be important in grooming, sensory stimulation, alleviating skin irritation, and reproductive behavior. Dust, which packs into the hair after wallowing, probably minimizes the effects of insects.
Wallows also serve as water reservoirs, making small ponds that become available to vertebrates and invertebrates for multiple uses; in addition, such ponds enhance growth of specific vegetation needing moist or wet habitat. Wallowing behavior also transports soils and seeds to other areas because the thick fur on the head and forequarters is ideal for dispersal of awned, barbed, and sticky materials.
Historically, the bison's most important predators were wolves. Wolves constantly followed the large herds, culling the old, incapacitated, and very young animals. Even solitary adult bulls were not immune to attack. To a lesser extent native human Americans were predators of the bison. Grizzlies occasionally killed bison, and mountain lions and coyotes were also occasional opportunistic predators of young calves.
But one of the primary killers, before the slaughter by humans in the late 1800s, were iced-over rivers. Thousands of bison drowned, particularly in the northern U.S., when the enormous weight of crossing herds caused the ice to give way.
Since the wolf and grizzly bear are gone from the tallgrass prairie region, man is the remaining predator. The Nature Conservancy has no plans to reintroduce wolves to the Tallgrass Prairie. It isn't big enough and they and our neighbors' cattle wouldn't mix well; so that means no wolves - ever!
Bison are ordinarily mild-mannered, but can be aggressive.