Bison

A bison is a large bovine in the genus Bison within the tribe Bovini. Two extant and numerous extinct species are recognised.
Of the two surviving species, the American bison, B. bison, found only in North America, is the more numerous. Although colloquially referred to as a buffalo in the United States and Canada, it is only distantly related to the true buffalo. The North American species is composed of two subspecies, the Plains bison, B. b. bison, and the generally more northern wood bison, B. b. athabascae. A third subspecies, the eastern bison is no longer considered a valid taxon, being a junior synonym of B. b. bison. Historical references to "woods bison" or "wood bison" from the Eastern United States refer to this synonym animal, not to B. b. athabascae, which was not found in the region. Its European kind B. bonasus or wisent —also 'zubr' or colloquially 'European buffalo'— is found in Europe and the Caucasus, reintroduced after being extinct in the wild.
While bison species have been traditionally classified in their own genus, modern genetics indicates that they are nested within the genus Bos, which includes, among others, cattle, yaks and gaur, being most closely related to yaks.

Description

The American bison and the European bison are among the largest surviving terrestrial animals in North America and Europe. They are typical artiodactyl ungulates, and are similar in appearance to other bovines such as cattle and true buffalo. They are broad and muscular with shaggy coats of long hair. Adults grow up to in height and in length for American bison and up to in height and in length for European bison. American bison can weigh from around and European bison can weigh from. European bison tend to be taller than American bison.
Bison are nomadic grazers and travel in herds. The bulls leave the herds of females at two or three years of age, and join a herd of males, which usually are smaller than female herds. Mature bulls rarely travel alone. Towards the end of the summer, for the reproductive season, the sexes necessarily commingle.
American bison are known for living in the Great Plains, but formerly had a much larger range, including much of the eastern United States and parts of Mexico. Both species were hunted close to extinction during the 19th and 20th centuries, but have since rebounded. The wisent in part owes its survival to the Chernobyl disaster, as the Chernobyl Exclusion Zone has become a kind of wildlife preserve for wisent and other rare megafauna such as the Przewalski's horse, though poaching has become a threat in the 21st century. The American Plains bison is no longer listed as endangered, but this does not mean the species is secure. Genetically pure B. b. bison currently number only about 20,000, separated into fragmented herds—all of which require active conservation measures. The wood bison is on the endangered species list in Canada and is listed as threatened in the United States, though numerous attempts have been made by beefalo ranchers to have it entirely removed from the Endangered Species List.
Although superficially similar, physical and behavioural differences exist between the American and European bison. The American species has 15 ribs, while the European bison has 14. The American bison has four lumbar vertebrae, while the European has five. Adult American bison are less slim in build and have shorter legs. American bison tend to graze more, and browse less than their European relatives. Their anatomies reflect this behavioural difference; the American bison's head hangs lower than the European's. The body of the American bison is typically hairier, though its tail has less hair than that of the European bison. The horns of the European bison point through the plane of their faces, making them more adept at fighting through the interlocking of horns in the same manner as domestic cattle, unlike the American bison, which favours butting. American bison are more easily tamed than their European cousins, and breed with domestic cattle more readily.

Evolution and genetic history

The bovine tribe split about 5 to 10 million years ago into the buffalos and a group leading to bison and taurine cattle. Genetic evidence from nuclear DNA indicates that the closest living relatives of bison are yaks, with bison being nested within the genus Bos, rendering Bos without including bison paraphyletic. While nuclear DNA indicates that both extant bison species are each other's closest living relatives, the mitochondrial DNA of European bison is more closely related to that of domestic cattle and aurochs. This discrepancy is either suggested to be the result of incomplete lineage sorting or ancient introgression. Bison are widely believed to have evolved from a lineage belonging to the extinct genus Leptobos during the Late Pliocene to Early Pleistocene in Asia. The earliest members of the bison lineage, known from the Late Pliocene to Early Pleistocene of the Indian Subcontinent and China, approximately 3.4-2.6 million years ago are placed in the subgenus Bison ''. The oldest remains of Eobison in Europe are those Bison georgicus found in Dmanisi, Georgia, dated to around 1.76 Ma. More derived members of the genus are placed in the subgenus Bison, which first appeared towards the end of the Early Pleistocene, around 1.2 Ma, with early members of the subgenus including the widespread Bison schoetensacki.
The steppe bison first appeared during the mid-Middle Pleistocene in eastern Eurasia, and subsequently became widely distributed across Eurasia. During the late Middle Pleistocene, around 195,000-135,000 years ago, the steppe bison migrated across the Bering land bridge into North America, becoming ancestral to North American bison species, including the large Bison latifrons, and the smaller Bison antiquus, which became extinct at the end of the Late Pleistocene. Modern American bison are thought to have evolved from B. antiquus during the Late Pleistocene-Holocene transition via the intermediate form Bison occidentalis. The European bison, Bison bonasus, first appeared in Europe during the late Middle Pleistocene, where it existed in sympatry with the steppe bison. Its relationship with other extinct bison species is unclear, though it appears to be only distantly related to the steppe and American bisons, with possibly some interbreeding between the two lineages during the Middle Pleistocene. The steppe bison survived into the early-mid Holocene in Alaska-Yukon and eastern Siberia, before becoming extinct.
Prior to the late 19th century, the population of American bison likely numbered in the tens of millions, perhaps as many as 60 million. During the population bottleneck caused by the great slaughter of American bison during the 19th century, the number of bison remaining alive in North America declined to as low as 541. During that period, a handful of ranchers gathered remnants of the existing herds to save the species from extinction. These ranchers bred some of the bison with cattle in an effort to produce "cattleo". Accidental crossings were also known to occur. Generally, male domestic bulls were crossed with bison cows, producing offspring of which only the females were fertile. The crossbred animals did not demonstrate any form of hybrid vigor, so the practice was abandoned. Wisent-American bison hybrids were briefly experimented with in Germany and a herd of such animals is maintained in Russia. First-generation crosses do not occur naturally, requiring caesarean delivery. First-generation males are infertile. The U.S. National Bison Association has adopted a code of ethics that prohibits its members from deliberately crossbreeding bison with any other species. In the United States, many ranchers are now using DNA testing to cull the residual cattle genetics from their bison herds. The proportion of cattle DNA that has been measured in introgressed individuals and bison herds today is typically quite low, ranging from 0.56 to 1.8%.
There are also remnant purebred American bison herds on public lands in North America. Two subspecies of bison exist in North America: the plains bison and the wood bison. Herds of importance are found in Yellowstone National Park, Wind Cave National Park in South Dakota, Blue Mounds State Park in Minnesota, Elk Island National Park in Alberta, and Grasslands National Park in Saskatchewan. In 2015, a purebred herd of 350 individuals was identified on public lands in the Henry Mountains of southern Utah via genetic testing of mitochondrial and nuclear DNA. This study, published in 2015, also showed the Henry Mountains bison herd to be free of brucellosis, a bacterial disease that was imported with non-native domestic cattle to North America.
In 2021, the American Society of Mammalogists considered Bison to be a subgenus, and placed both bison species back into Bos''.
Relationships of bovines based on nuclear DNA, after Sinding, et al. 2021.

Behavior

is a common behavior of bison. A bison wallow is a shallow depression in the soil, either wet or dry. Bison roll in these depressions, covering themselves with mud or dust. Possible explanations suggested for wallowing behavior include grooming behavior associated with moulting, male-male interaction, social behavior for group cohesion, play behavior, relief from skin irritation due to biting insects, reduction of ectoparasite load, and thermoregulation. In the process of wallowing, bison may become infected by the fatal disease anthrax, which may occur naturally in the soil.
Bison temperament is often unpredictable. They usually appear peaceful, unconcerned, or even lazy, but they may attack without warning or apparent reason. They can move at speeds up to and cover long distances at a lumbering gallop.
Their most obvious weapons are the horns borne by both males and females, but their massive heads can be used as battering rams, effectively using the momentum produced by what is a typical weight of moving at. The hind legs can also be used to kill or maim with devastating effect. In the words of early naturalists, they were dangerous, savage animals that feared no other animal and in prime condition could best any foe except for a brown bear or a pack of wolves.
The rutting, or mating, season lasts from June through September, with peak activity in July and August. At this time, the older bulls rejoin the herd, and fights often take place between bulls. The herd exhibits much restlessness during breeding season. The animals are belligerent, unpredictable, and most dangerous.