American Bison (7)
|We saw a lot of bison herds. Sometimes they blocked the roads. These photos are made from the car window.In the workshop a profile photo. |
The American bison (Bison bison), also commonly known as the American buffalo or simply buffalo, is a North American species of bison that once roamed the grasslands of North America in massive herds. They became nearly extinct by a combination of commercial hunting and slaughter in the 19th century and introduction of bovine diseases from domestic cattle, and have made a recent resurgence largely restricted to a few national parks and reserves. Their historical range roughly comprised a triangle between the Great Bear Lake in Canada's far northwest, south to the Mexican states of Durango and Nuevo León, and east to the Atlantic Seaboard of the United States (nearly to the Atlantic tidewater in some areas) from New York to Georgia and per some sources down to Florida.
Two subspecies or ecotypes have been described: the plains bison (B. b. bison), smaller in size and with a more rounded hump, and the wood bison (B. b. athabascae)—the larger of the two and having a taller, square hump. Furthermore, the plains bison has been suggested to consist of a northern (B. b. montanae) and a southern subspecies, bringing the total to three. However, this is generally not supported. The wood bison is one of the largest wild species of bovid in the world, surpassed by only the Asian gaur and wild water buffalo. It is the largest extant land animal in the Americas.
A bison has a shaggy, long, dark-brown winter coat, and a lighter-weight, lighter-brown summer coat. As is typical in ungulates, the male bison is slightly larger than the female and, in some cases, can be considerably heavier. Plains bison are often in the smaller range of sizes, and wood bison in the larger range. Head-and-body lengths range from 2 to 3.5 m long, the tail adding 30 to 91 cm. Shoulder heights in the species can range from 152 to 186 cm. Weights can range from 318 to 1,000 kg. The heaviest wild bull ever recorded weighed 1,270 kg. When raised in captivity and farmed for meat, the bison can grow unnaturally heavy and the largest semidomestic bison weighed 1,724 kg. The heads and forequarters are massive, and both sexes have short, curved horns that can grow up to 61 cm long, which they use in fighting for status within the herd and for defense.
Bison are herbivores, grazing on the grasses and sedges of the North American prairies. Their daily schedule involves two-hour periods of grazing, resting, and cud chewing, then moving to a new location to graze again. Bison mate in August and September; gestation is 285 days. A single reddish-brown calf nurses until the next calf is born. If the cow is not pregnant, a calf will nurse for 18 months. At three years of age, bison cows are mature enough to produce a calf. Bison bulls of that age may try to mate with cows, but if more mature bulls are present, they may not be able to compete until they reach five years of age. Bison have a life expectancy around 15 years in the wild and up to 25 years in captivity.
American bison live in river valleys, and on prairies and plains. Typical habitat is open or semiopen grasslands, as well as sagebrush, semiarid lands, and scrublands. Some lightly wooded areas are also known historically to have supported bison. Bison also graze in hilly or mountainous areas where the slopes are not steep. Though not particularly known as high-altitude animals, bison in the Yellowstone Park bison herd are frequently found at elevations above 8,000 feet and the Henry Mountains bison herd is found on the plains around the Henry Mountains, Utah, as well as in mountain valleys of the Henry Mountains to an altitude of 10,000 feet.
Behavior and ecology
Bison are migratory and herd migrations can be directional as well as altitudinal in some areas. Bison have usual daily movements between foraging sites during the summer. In a montane valley, bison have been recorded travelling, on average, 3.2 km a day. The summer ranges of bison appear to be influenced by seasonal vegetation changes, interspersion and size of foraging sites, the rut, and the number of biting insects. The size of preserve and availability of water may also be a factor. Bison are largely grazers, eating primarily grasses and sedges. On shortgrass pasture, bison predominately consume warm-season grasses. On mixed prairie, cool-season grasses, including some sedges, apparently compose 79–96% of their diet. In montane and northern areas, sedges are selected throughout the year. Bison also drink water or consume snow on a daily basis.
Social behavior and reproduction
Female bison live in maternal herds which include other females and their offspring. Male offspring leave their maternal herd when around three years old and either live alone or join other males in bachelor herds. Male and female herds usually do not mingle until the breeding season, which can occur from July through September. However, female herds may also contain a few older males. During the breeding season, dominant bulls maintain a small harem of females for mating. Individual bulls "tend" cows until allowed to mate, by following them around and chasing away rival males. The tending bull shields the female's vision with his body so she will not see any other challenging males. A challenging bull may bellow or roar to get a female's attention and the tending bull has to bellow/roar back. The most dominant bulls mate in the first 2–3 weeks of the season. More subordinate bulls mate with any remaining estrous cow that has not mated yet. Male bison play no part in raising the young.
Bison herds have dominance hierarchies that exist for both males and females. A bison's dominance is related to its birth date. Bison born earlier in the breeding season are more likely to be larger and more dominant as adults. Thus, bison are able to pass on their dominance to their offspring as dominant bison breed earlier in the season. In addition to dominance, the older bison of a generation also have a higher fertility rate than the younger ones. Cows nurse their calves for at least 7 or 8 months, but most calves seem to be weaned before the end of their first year.
Bison have been observed to display homosexual behaviors, males much more so than females. In the case of males, it is unlikely to be related to dominance, but rather to social bonding or gaining sexual experience.
While often secure from predation because of their size and strength, in some areas, bison are regularly preyed upon by wolves. Wolf predation typically peaks in late spring and early summer, with attacks usually being concentrated on cows and calves. Wolves more actively target herds with calves than those without. The length of a predation episode varies, ranging from a few minutes to over nine hours. Bison display five apparent defense strategies in protecting calves from wolves: running to a cow, running to a herd, running to the nearest bull, running in the front or center of a stampeding herd, and entering water bodies such as lakes or rivers. When fleeing wolves in open areas, cows with young calves take the lead, while bulls take to the rear of the herds, to guard the cows' escape. Bison typically ignore wolves not displaying hunting behavior. Wolf packs specializing in bison tend to have more males, because their larger size than females allows them to wrestle prey to the ground more effectively. Healthy, mature bulls in herds rarely fall prey. Grizzly bears can also pose a threat to calves and sometimes old, injured, or sick adult bison.
Dangers to humans
Bison are among the most dangerous animals encountered by visitors to the various U.S. and Canadian national parks and will attack humans if provoked. They appear slow because of their lethargic movements, but can easily outrun humans; bison have been observed running as fast as 64 km/h.
Between 1980 and 1999, more than three times as many people in Yellowstone National Park were injured by bison than by bears. During this period, bison charged and injured 79 people, with injuries ranging from goring puncture wounds and broken bones to bruises and abrasions. Bears injured 24 people during the same time. Three people died from the injuries inflicted—one person by bison in 1983, and two people by bears in 1984 and 1986.
Source: Parts from Wikipedia