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Mother with calf © Chris Helzer

Bison are the largest land mammals in North America

Roaming the Fields of America's Heartland

Once a staple for some Native Americans, millions of American bison roamed from Canada to Mexico and New York to California, until wholesale slaughter by American settlers brought them to the brink of extinction in the early 20th century. At the end of the slaughter, less than 100 free-roaming bison remained in the world.

Thanks in large part to the efforts of the American Bison Society, the species has rebounded, and herds have been built up in preserves, where they live in a semi-wild state. However, genetic diversity remains a concern because the population was bred from such reduced numbers. Individuals also mate with vastly different success rates, further limiting the available gene pool.

The largest land mammal in North America, adult males may stand as tall as six feet at the shoulders and weigh 1000-2000 pounds. Bison are grazers, traveling between pastures in groups ranging from family units to large herds. They feed in the morning and evening, mostly on grasses and sedges, and rest during the day, chewing cud or wallowing in mud to rid themselves of parasites. During mating season, which begins in July and can last as late as September, bulls will fight amongst themselves for cows. After a nine month gestation, a single calf is born per cow, suckles for 12 months, and remains with her until sexual maturity, which occurs around three years of age for females and six years for males.