Bison

views updated

Bison

The American bison (Bison bison ) is a large, herbivorous land mammal native to the grasslands and open forests of North America. It is a member of the family Bovidae, which also includes cattle, sheep, and goats. When French explorers first saw these large, shaggy, cow-like animals, they called them boeufs, the French word for “cattle.” This later became anglicized into the word “buffalo,” a name still applied to the bison, despite the fact that there are other bovids in Africa and Asia more properly known as buffalo.

There are two subspecies of American bison, the plains bison (B. b. bison ) and the wood bison (B. b. athabascae ). The wood bison lives west and north of the plains bison, and is larger and darker in color. Because its habitat is open woodland and muskeg, it does not live in such huge herds as the plains bison once did. However, some taxonomists do not recognize wood bison and plains bison as separate subspecies.

Bison probably came to North America from Eurasia during the most recent ice age. They did this perhaps 25,000 years ago, by traveling along a land-bridge across the present-day Bering Strait. The land-bridge existed because sea level was lower then, owing to so much of Earth’s water being on land in the form of glacial ice. The only Eurasian remnant is the European bison or wisent (B. bonasus ), which now only survives in a few small free-ranging and captive herds (about 2,900 animals as of 2000) in Belorussia, Poland, Ukraine, and Russia. Another population of wisents in the Caucasus Mountains became extinct in 1925. The wisent is somewhat smaller than the American bison and does not have as large a hump.

America’s largest mammal

The male (or bull) bison can reach 6.5 ft (2 m) in height and measure up to 12 ft (3.7 m) long, and is twice as large as the female (or cow). Male bison commonly weigh 2, 000 lb (900 kg), but animals twice as large have been reported. American bison have a huge hump across the shoulders, which rises 1 ft (30 cm) or more above the top of their head. The dark brown hair growing on the hump is long and shaggy, and the thick body fur allows bison to tolerate air temperatures as low as -49°F (-45°C). In the spring, bison molt their winter coat and great quantities of their hair falls off. The back half of their body has short, lighter-colored hair. The head is covered with a helmet of thick black hair that terminates under the chin as a “goatee.” Extremely rare white bison are revered by Native Americans of the Plains. When one was born in 1994, people traveled long distances to Wisconsin to see it. As the calf grew older, however, its fur turned darker.

Bison have large, curved, hollow horns growing sideways from their big, heavy head, which are never shed. The horns may reach a length of 24-26 in (60-65 cm), but are usually much shorter. The horns of females curve back toward the head more than that of males. Bison have no front teeth, and eat grass and other herbaceous plants by wrapping them around their tongue and pulling to break them off the root-stock. Bison are ruminant animals. As such, they have a four-chambered stomach and chew a cud.

Their short tail is used both as a flyswatter and as an indicator of excitement, for the normally drooping tail rises into the air when a bison is angry or otherwise excited. Bison are subject to attack by numerous biting flies and ticks, and they have a habit of rolling in dirt or mud to relieve their itchiness. Because of their hump they cannot roll over completely, so they rock and kick first on one side and then on the other. This maneuver is called wallowing, and it also helps get rid of molting hair.

Life in the herd

Estimates of the prehistoric numbers of bison on the American plains, before the arrival of Europeans, vary from 30-80 million. At the time, bison were a “pantry on the hoof” for the Plains tribes of Native Americans, who used the animals for food, clothing, fuel, and shelter, killing only what they needed to survive.

Bison herds move around constantly in search of food and water, and typically travel several miles a day. Unlike many migrating animals, bison do not follow set paths each year, and even minor stimuli can change their direction of travel. This might be a strange scent in the wind, an unfamiliar animal crossing their path, or a dried-up water hole. The only set pattern to their migration is that they meander north to find a good place to raise their young in the summer, and then south to ride out the winter. The herd follows experienced, lead animals. Bison in herds continually make noises to each other, using roars, grunts, sneezing, snorts, and bawling to communicate different meanings.

The least hint of danger can set a herd stampeding across the prairie. The stampede speed may reach 35 mph (56 km/h), although they cannot keep that speed up for more than about half an hour. If running does not shake their pursuers, bison may turn abruptly and charge. The animal’s skull in the forehead is double-thick, protecting the brain from damage during impact.

Bison reproduction

In the early summer, bulls and cows gather for the rut. During the rut, bulls challenge each other for the right to mate with cows. Cows first mate when about two years old, but bulls do not do so until they are older and strong enough to challenge dominant males. A few loud roars and an enthusiastic demonstration of kicking and wallowing is usually enough to convince a lower-ranked bull to look elsewhere for a mate. Only rarely does an actual fight occur, when bulls lock horns and charge each other.

When a dominant bull selects a mate, he bonds with her by grazing side by side for some hours, away from the rest of the herd. After a brief nocturnal mating, the companionship may continue for a brief time, but then the male departs, looking for another female. The females usually mate only once.

The gestation period lasts nine-and-a-half months, and new calves are born in the spring. This begins about mid-April, though births may continue into the early autumn. Newborn calves are cinnamon-colored, weigh about 50 lb (23 kg), and can walk and nurse within 2-3 hours of birth. The calves start to eat grass within about 15 days, and at about two months of age their hump and horns begin to show and their coat darkens to the adult color. Bison typically live to an average age of about 20 years in the wild, but can reach 40 years in captivity.

The disappearing bison

The enormous bison herds of North America shrank rapidly in the face of relentless over-hunting during the westward migration of European settlement. The presence of bison conflicted with the aspirations of people looking for land to settle and farm,

KEY TERMS

Bovid— An animal of the Bovidae, or cow family, characterized by a grazing habit and having hollow horns.

Molt— To lose one type of hair in preparation for a new type to grow in. Bison molt twice a year as the seasons change.

Ruminant— A cud-chewing animal with a four-chambered stomach and even-toed hooves.

Rut— The period during which males challenge each other to acquire access to females.

Wallowing— Rolling and kicking in the dust to eliminate insect pests and scratch itchy skin.

and with the aims of government, which wanted to subdue the native tribes of Plains Indians. As the railroads were built through the Central Plains, travelers were encouraged to shoot bison from the windows of the train, for fun and excitement. The carcasses were often left to rot. More important, however, was the huge market hunt for the plains bison, with trainloads of butchered carcasses and hides being shipped to markets in American cities. By 1905, the excessive hunting resulted in only an endangered 500 bison left surviving on their range in the United States. A herd of endangered wood bison, discovered in northwestern Canada in 1957, is protected in Wood Buffalo National Park and nearby areas.

Although bison are still a threatened species, there has been some recovery and there are now substantial wild herds in some places, such as Yellowstone National Park. Some ranchers are raising semi-domestic animals and sell buffalo meat, which has less cholesterol than beef. It has even been suggested that herds of bison might once again be allowed to roam free on parts of the North American prairie, creating a tourist attraction to bring money to economically depressed areas. However, not much suitable habitat is left in a natural condition, and the enormous bison herds of the past will never again be seen.