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Bison management by the Conservancy is intended to help manage native landscapes for biodiversity. Bison produce disturbances through grazing and these associated impacts play a fundamental role in ensuring a dynamic spatial and temporal heterogeneity in grassland communities. In other words, grazing increases the plant diversity on a native prairie by producing a variety of disturbances. These disturbances cause the plant and animal communities to respond as it did when bison roamed Iowa. Grassland birds, butterflies and many prairie plants need a structurally diverse plant community with a variety of grass and forb species to thrive.
Bison make use of large amounts of relatively low quality forage — an important trait in adapting to the environment. Bison have a high degree of mobility and generally are not restricted by topography or distance from water.
Cattle and bison graze differently with bison being a superior choice for prairie restoration. Cattle and bison also have different environmental needs (see table below).
Like domestic cattle, bison are grazers. However, they prefer young, tender grasses and eat few forbs (such as wildflowers). In fact, a bison’s diet is composed of 99 percent grasses and sedges. 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. 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.
| Grazing Behavior | Bison have a much stronger herding instinct and are much more mobile. They tend to move constantly, even when grazing, producing a more intensive, short-duration grazing effect. |
| Diet | Bison consume a larger proportion of grasses and less forbs and shrubs. |
| Digestive | Bison more effectively digest low-quality forage. Cattle have greater digestive efficiency on high-quality (e.g., feedlot rations) diets. |
| Range Utilization | Bison grazing is less restricted by water availability, slope, elevation and shade. Bison are more attracted to preferred forage, such as the lush new grass that follows a fire. |
| Winter Foraging | In many areas, grass-fed cattle must be given protein supplement during the winter. Bison maintain themselves and have much lower weight losses on poor quality winter forage (cured, low-nutrient standing grass). Bison forage down through snow-cover and will eat snow to meet their water requirements. |
| Cold Stress | Bison have higher overall cold resistance: better insulation, lower winter metabolic rates and lower external critical temperature. |
| Habitat | Bison create and maintain wallowing areas (small-scale patch disturbances) and actively rub themselves on trees and other suitable objects. |
| General | Bison are hardy animals with natural resistance to bovine diseases and possess an exceptional ability to recuperate from injuries. They require less handling (once per year) and no growth hormones. With sufficient space, grass, water, herd age/sex structuring and sound fence construction (six-foot barbed-wire fence) containment is not a problem. |
Images (top to bottom, left to right): bison at Lame Johnny Creek Ranch, South Dakota © Bob Paulson/TNC, spring calf at Lame Johnny Creek Ranch, South Dakota © Bob Paulson/TNC
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