In May 2016, President Obama signed the National Bison Legacy Act into law, which made the American Bison (Bison bison) the national mammal of the United States. While 20-30 million bison used to roam across North America, unregulated shooting and habitat loss led to their population to fall to only 1,091 by 1889. Today there are about 500,000 bison in North America, although most are not pure wild bison - they've crossbred with cattle and are used for livestock. Fewer than 30,000 of the bison in North America are pure wild bison in conservation herds and even fewer, about 5,000, are unfenced and disease-free.
Even with the recovery of bison across North America, they are still considered ecologically extinct through much of their historic range, except in the few national parks and other small wildlife areas where herds are kept.
Bison are an important prairie species. The way they graze creates a variety of small disturbances that end up contributing to increased plant diversity. In native prairies, bison eat a large quantity of relatively low quality forage. Bison are better for prairie restoration than cattle as they eat more grasses and sedges, whereas cattle tend to eat more forbs and shrubs. Bison will also rub on young trees and prevent them from invading the prairie.
There are two subspecies of bison: the plains bison (Bison bison bison) and the wood bison (Bison bison athabascae). The wood bison ranged primarily throughout Canada and Alaska. The plains bison was concentrated in the Great Plains, but could be seen in nearly every continental state, southern Canada and northern Mexico. The plains bison was the subspecies found in Iowa. Currently there are a few managed herds of bison in Iowa, though none are managed by the Iowa DNR. If you’d like to see some roaming bison, two places you can go are Neal Smith National Wildlife Refuge near Prairie City and Broken Kettle Grasslands (managed by The Nature Conservancy) north of Sioux City. Both of these herds are used for prairie management.