Fast Facts
Distribution
Herds located in Delta Junction, Copper River, Chitina River, and Farewell.
Diet
Herbivorous; bison graze on sedges, grasses, and sometimes willow and dwarf birch.
Predators
Wolves and grizzly bears.
Reproduction
Single calves are most common, but twinning can occur.
Remarks
Nearing extinction in the late 1800s, bison have bounced back and exist in Alaska in large numbers now.
The American bison occurs in two subspecies in North America, the plains bison (Bison bison bison) and the wood bison (Bison bison athabascae). Plains bison are somewhat smaller than wood bison. A bison’s head and forequarters are massive and seem out of proportion to the smaller hindquarters. A bison’s backbone begins to rise just ahead of the hips and reaches its maximum height about or behind the front shoulder. From above the shoulder, the hump drops almost straight down to the neck. In wood bison, the hump is taller and the highest point of the hump is further forward than in plains bison.
Bison have horns that curve upward. The horns of a bull are larger and heavier than the horns of a cow. In late fall, a bison’s coat is a rich, dark brown. As winter progresses, the coat changes color and is lighter colored by spring. When the weather warms, the hair loosens and hangs in patches until it is completely shed and replaced with new hair in the late spring. The hair on the chin resembles a goatee and is more pointed in wood bison. Older animals tend to have more hair on their heads.
The American bison occurs in two subspecies in North America, the plains bison (Bison bison bison) and the wood bison (Bison bison athabascae). Plains bison are somewhat smaller than wood bison. A bison’s head and forequarters are massive and seem out of proportion to the smaller hindquarters. A bison’s backbone begins to rise just ahead of the hips and reaches its maximum height about or behind the front shoulder. From above the shoulder, the hump drops almost straight down to the neck. In wood bison, the hump is taller and the highest point of the hump is further forward than in plains bison.
Bison have horns that curve upward. The horns of a bull are larger and heavier than the horns of a cow. In late fall, a bison’s coat is a rich, dark brown. As winter progresses, the coat changes color and is lighter colored by spring. When the weather warms, the hair loosens and hangs in patches until it is completely shed and replaced with new hair in the late spring. The hair on the chin resembles a goatee and is more pointed in wood bison. Older animals tend to have more hair on their heads.
Most bison calves are born in May; however, they can be born from April to August or even later. Newborn calves have a reddish coat. They are able to stand when only 30 minutes old and within a few hours can run and kick their hind legs in the air. Calves start grazing at about 6 days of age, but they are not completely weaned until a few months later. Their reddish-orange coat begins to darken at about 10 weeks and turns dark brown about 5 weeks later. Cows are sexually mature at 2 years of age and give birth to a single calf in two out of three years on average, after a gestation period of about 9 months. Bison in Alaska have been known to live a relatively long time compared to other hoofed animals. One tagged bull in the Copper River area was over 20 years old.
Bison are grazing animals and in Alaska find food in meadows, around lakes, along rivers and in recent burns. Their diet consists mainly of various grasses, sedges, and forbs including vetch, a favored summer food found on gravel bars. Bison also eat silverberry, willow, and dwarf birch. Good bison habitat is now more limited than it was several thousand years ago, but the available habitat in Interior Alaska can still support several thousand of these animals
Various forms of bison existed in Alaska for several hundred thousand years; until relatively recent times, bison were one of the most abundant large animals on the landscape. Alaska’s existing wild plains bison are descendants of animals that were transplanted from Montana in 1928 to Delta Junction. Transplants have created additional herds at Copper River, Chitina River, and Farewell. Small domestic herds are located in agricultural areas on the mainland and on Kodiak and Popov Islands.
Bison tend to remain in a home range, although they often move between seasonal ranges. Alaska’s wild bison do not remain in single herds, but occur alone or in groups ranging up to several hundred animals or more. In the Delta Junction area, they move up the Delta River in early spring to secluded meadows where they calve. This herd continues to move about in the area throughout the year. Alaska’s other wild bison herds also show seasonal movement patterns.
During the Ice Age, steppe bison, the ancestors of modern bison, migrated into Alaska from Asia, crossing the Bering Land Corridor. Far larger than modern buffalo, with longer horns, these giant herbivores shared the tundra of prehistoric Alaska with wild horses, wooly mammoths, and western camels.
As ice sheets advanced and retreated, the migratory bison dispersed across North America. Temporary advancements of glaciers isolated populations, and bison evolved into two subspecies, wood bison and the smaller plains bison. The giant longhorn steppe bison became extinct.
Wood bison adapted to life in the north, grazing in the boreal meadows and forests of Alaska and Canada. The smaller plains bison thrived further south, and formed the famous buffalo herds of the American Great Plains.
Wood bison disappeared from Alaska several hundred years ago, probably the result of hunting and changing habitat.