E-Fauna BC: Electronic Atlas of the Wildlife of British Columbia

Bison bison (Linnaeus)
American Bison; Bison; Buffalo
Family: Bovidae
Species account author: David Shackleton
Extracted from the Hoofed Mammals of British Columbia

Photo of species

© David Shackleton  Email the photographer   (Photo ID #95473)

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Distribution of Bison bison in British Columbia.
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Source: Hoofed Mammals of British Columbia by David Shackleton © Royal BC Museum
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Introduction


Two subspecies of Bison are recognized in British Columbia: Wood Bison (Bison bison athabascae) and Plains Bison (Bison bison bison). Subspecies descriptions are found in the Additional Notes section below.

Species Information

Bison is the largest of B.C.’s ungulates. It is characterized by massive forequarters, small hindquarters, and a large head and short neck. The nose is black, square and naked, and has large nostrils. The tail is shorter than what you would expect for an animal of this size; it is covered with short hairs, except at the end where there is a tuft of long black hairs similar to that found in Domestic Cattle. Wood Bison can have longish hairs all along the tail in winter pelage. Male Bison also have a noticeable tuft of hair on the end of the penis sheath. The massive forequarters relative to the hindquarters, are created by the large hump above the shoulders that is the result of the elongated spines of the thoracic vertebrae. The hump is especially large in adult males, rising abruptly about 400 mm or more from just behind the head.

The Bison’s coat is dark brown, but can be bleached lighter before the end of winter, especially in older males. The head is covered by darker, almost black hair, and in both sexes the hair between the horns forms a roll or mop that can extend below and behind horns to cover the ears in adult males. This mop of hair between the male’s horns may be worn off by the end of the rut. The forehead profile of adult males is also strongly convex due to its covering of long hairs. Both sexes have a noticeable beard of long hair below the chin. Generally, the beard is roughly pointed, but may develop a rounded or bulbous end in adult males. In both males and females, a fringe of long, dark hair runs along the lower margin of the neck as far as the chest to form a mane. In summer especially, the pelage of adult males is unique, with a cape of long, dense curly hairs on the anterior part of the body to just behind the shoulders, and short hair over the hindquarters. The long hair also extends down the front legs to about 10 cm above the hooves, creating the appearance of chaps or pantaloons. The cape and chaps are much less pronounced in females. The colour of the cape can range from burned sienna to reddish brown on the top and front, grading into black-brown below on the forelegs. Adult females are clearly smaller than adult males in both shoulder height and weight, being about 55 per cent of the males’ weight.

Young Bison are reddish brown for the first three months of life, after which their coat colour changes to a dark brown, resembling that of the adults. White Bison are extremely rare, though not unknown, and have great significance for many First Nations of the Plains. This colour form has not been reported in B.C.

In both sexes, the horns are short and curved, with sharp points. They are usually black, but can sometimes appear dark grey against the black hair of the head. With a round cross-section, the basal horn diameter is much larger in males than in females. The horn sheaths extend laterally from the head before curving sharply upward and inward. The skull is large with a broad, convex forehead, mildly protruding tubular orbits, and bone cores that project laterally in a gentle curve from the cranium. The occipital region above the condyles is flat or convex in shape.

Identification and Subspecies Information

Subspecies: Wood Bison (Bison bison athabascae)

Subspecies Description:

There is disagreement among biologists about the characteristics and even the existence of the Wood Bison as a separate subspecies. For example, in a recent scientific paper that re-evaluated earlier published conclusions, one of the researchers stated that the external characteristics he had used to separate the Wood Bison from the Plains Bison did not seem to hold up when he examined a larger sample size.

The Wood Bison is supposedly larger in body and skull dimensions, and darker in coat colour than the Plains Bison. Its display hairs are shorter, as are the hairs on the head, beard, neck mane, chaps and penis sheath tuft; this makes the head and forequarters appear smaller than those of the Plains Bison. Conversely, the Wood Bison’s tail has more hair along its length than the Plains Bison’s. Its cape may also be darker.

Measurements:

total length: male: 3,551 mm, (3,180-3,890) n = 14; female: 2,976 mm (2,650-3,330) n = 7
tail vertebrae: male: 496 mm (440-540) n = 14; female: 422 mm (390-480) n = 7
hind foot: male: 663 mm (620-710) n = 14; female: 615 mm (590-660) n = 6
shoulder: male: 1,822 mm (1,680-2,010) n = 14; female: 0-1,720) n = 7
weight: male: 943.6 kg (759-1,179) n = 11; female: 508 kg n = 1
skull length: male 528.2 (485-555) n = 19; female: 467 mm n = 1
skull width male: 249.0 mm (231-268) n = 7

Range:

Wood Bison have been reintroduced into British Columbia, or have dispersed naturally from nearby herds living outside the province. There are currently four populations in B.C. The most northern population lives mainly along the west side of the Liard River near the border of the Northwest Territories, and south to around the junction of the Liard and Crow rivers. These animals belong to the population introduced to the Nahanni Butte area of the Northwest Territories. A second B.C. population lives on the north side of the Liard River about 80 km west and upstream of the more northern herd. The other two populations of Wood Bison extend into B.C. along the Alberta border. One, along the Hay River, spends most of its time on the Alberta side near Zama Lake and only occasionally moves into B.C. The other inhabits an area 80 km to the south, around the Etthithun Lake area and the headwaters of the Kahntah River, between 58° to about 57° 50’ N latitude. All these transplanted Wood Bison originated from the herd in the southern part of Elk Island National Park, Alberta. Opportunities to observe Wood Bison in B.C. are extremely limited due to their low numbers and isolated ranges, but the area around Etthithun Lake does have vehicle access.

Conservation Status:

In 1977, about 100 Wood Bison were estimated in B.C. This subspecies is listed nationally by COSEWIC as threatened.

Subspecies: Plains Bison (Bison bison bison)

Measurements:

total length: male: 3,315 mm (3,042-3,400) n = 5; female: 2,386 mm (2,130-2,890) n = 3
tail vertebrae: male: 399 mm (304-380) n = 4 female: 421 mm (304-508) n = 3
hind foot: male: 595 mm (530-680) n = 4; female: 515 mm (508-530) n = 3
ear: male: 150 mm n = 1
shoulder height: male: 1,783 mm (1,670-1,890) n = 7; female: 1,520 mm (1,370-1,670) n = 3
weight: male: 832.2 kg (720-998) n = 5; female: 452.5 kg (360-545) n = 6
skull length: male: 486.6 mm (450-520) n = 77; female: 443.4 mm (415-468) n = 25
skull width: male: 238.8 mm (222-252) n = 77; female: 207.6 mm (195-219) n = 29

Range:

The single free-ranging Plains Bison population in British Columbia occupies an area west of Sikanni Chief and Pink Mountain northwest of Fort St John, from just north of Trimble Lake and the Sikanni River, to the south side of the Halfway River. This population originated from a private introduction of wild Plains Bison from the northern part of Elk Island National Park in 1971, to a farm near Pink Mountain. The animals escaped shortly after arriving. These Plains Bison now occupy an area that is difficult for visitors to reach, so observing them is a problem. But several ranches in the northeastern part of the province raise Plains Bison, and while their animals are often de-horned for production purposes, they probably provide the best chances of seeing this magnificent species in B.C.

Conservation

Plains Bison is on the provincial [Red List], and 1997 a total of around 1,500 were estimated in the free-ranging population. Even though released into the historic Wood Bison range, this free-ranging Plains Bison herd in British Columbia is the largest herd free of problem-diseases (e.g.anthrax, brucellosis) in the world, and along with the Yellowstone National Park herd in Wyoming is considered one of the world's largest populations of this subspecies. As such, the B.C. herd is of major conservation significance for the species and its genotype; a management focus in B.C. should be to ensure it does not interbreed with animals from the Wood Bison herds.

Biology

Identification

Bison is a massive, bulky animal, as large or larger than Domestic Cattle. Its size, together with the obvious shoulder hump and disproportionately smaller hindquarters in lateral profile, distinguish it from the almost horizontal profile of the back of Cattle. Bison can also be identified by their dark brown shaggy coat in winter, and distinct cape of long hairs over the forequarters in summer. Other unique characteristics of Bison are the beard and the mop of hair on the top of the head between the horns. Both are especially noticeable in males, particularly the large dark broad head of adults. These characteristics make it difficult to confuse Bison with any other ungulate in the province.

The forehead of the skull is wide between the orbits, and the somewhat tubular orbits project from the sides of the head in adult males. The pointed bone cores, present in both sexes project laterally from behind the orbits in a gentle upward curve, and usually have a strongly ridged surface in adult males. These characteristics make the skull readily distinguishable from all but Domestic Cattle. Bison skulls differ from those of Cattle in the occipital region and skull shape. The Bison skull is much more obviously tapered from rear to front than that of Cattle. The forehead is also broader and more convex, while the orbits are more tubular and often protrude more than those of Cattle. In dorsal view, the bone cores of Bison leave the frontal bones anterior to the para-occipital crest, whereas the cores of Cattle leave the frontal bones in line with this crest. The shape of the para-occipital crest is mildly convex in Bison, but has two bulges on either side of the centre line in Cattle. In lateral profile, the occipital region above the condyles is concave in Cattle and convex or flat in Bison.

Tracks of Bison are similar to those of Cattle, and for most of us probably indistinguishable in the field. But in areas where there are no Cattle, the large size and rounded shape of the hoof prints are characteristic of Bison. The only other species with similarly round, semi-circular-shaped hooves is Caribou, but their tracks are smaller and distinctly sausage-shaped, with clear indications of dew claws, which in Bison are not seen unless the ground is soft and the animals have sunk in to some depth. Moose and Elk have similar-sized tracks to Bison, but Moose tracks are pointed and much narrower, and Elk tracks are less rounded and narrower. Bison faeces are almost identical to those of Cattle, varying in shape and consistency with seasonal changes in food.
Reproduction

The gestation period is between 277 and 293 days, and births take place from late April to June, sometimes into July. Females usually give birth within the herd, although some may leave for a few days. A single calf is born, weighing between 14 and 18 kg; twins are extremely rare. Calves under three months of age, are readily distinguished by their bright reddish brown coat; the reason for this distinct colour is unknown. Female Bison are protective mothers and their young are followers, staying with them until at least their first winter, although the bond between them begins to weaken noticeably in the mating season. In one instance in the Northwest Territories, herd members were seen to protect a calf from Wolves, but how frequently this cooperative behaviour happens is unknown.

The growth rate of female Bison slows around 3 to 4 years of age, but in males continues until about 5 or 6 years of age. Game ranchers report that males in captivity can continue growing even longer. Most healthy female Bison bear their first young on their third birthday, but some give first birth a year sooner or later. Under favourable conditions, most females produce one young each year throughout their life; in poorer environments, they may only bear two calves every three years. Male Bison, like many wild ungulates, are sexually mature around 18 months old, but do not usually begin to be fully active in mating until at least 6 or 7 years of age.
Diet

Bison are primarily grazers, eating sedges, grasses, rushes and forbs, but they also eat some browse species. A study of Wood Bison in the Slave River lowlands, Northwest Territories, identified 29 different plant categories in the diet and that the main plants eaten year round were Slough Sedge and reedgrass. Bison in other areas of North America feed mainly on grasses in summer and sedges in winter, and others feed mainly on grasses year round. It appears that the range of digestible forages available to Bison determines the array of plant species they eat. In comparison to Domestic Cattle, Bison appear to digest forages more efficiently, especially those of low quality. In winter, rather than using their front feet to paw through the snow to forage, as many ungulates do, Bison sweep their heads from side to side to clear snow from vegetation.
Age determination and life expectancy

In the field, horn shape and size can be used to determine the approximate age of a Bison up to about 6 or 7 years in males and 3 to 4 years in females. Bison of both sexes can live more than 20 years, but the average life span is probably between 10 and 15 years.
Predators and other mortality factors

Wolves are the main predators of Bison; Grizzly Bears prey on them occasionally. Other species such as Coyote and Wolverine may only scavenge on carcasses of animals killed by larger predators, disease or old age. The diseases important in the management of Bison include brucellosis, tuberculosis and anthrax, all probably introduced to North America by Domestic Cattle. None have been diagnosed in free-ranging Wood or Plains bison populations in British Columbia. Other Domestic Cattle diseases, such as respiratory viruses, Bovine Virus Diarrhoea virus and gastrointestinal parasites, have been found in captive Bison. Disease transmission to and from Domestic Cattle is potential wherever free-ranging Bison herds contact ranched Bison or Cattle herds. Another mortality factor, both historical and current, is death by drowning. This happens when Bison herds break through thin ice while crossing large rivers or lakes in late fall and early spring.
Social organization, grouping and behaviour

Bison are a social species, living in groups year round. Typically, adult males live apart from females and younger animals, so there are all-male groups and much larger maternal groups. Lone adult males of all ages are also not uncommon. Young males usually leave their maternal group when about four years old. Group size varies greatly depending on population size and density, habitat, and season. The largest groups form during the rut. When Europeans first came to North America, they reported seeing Bison herds containing thousands of individuals. Today, in large populations, maternal and rutting groups of more than 100 are common; the maximum group size is often limited by the habitat. The more open and large the meadow, the larger the group; groups in forested habitats are small. Bison constantly vocalize in a group, uttering short grunts as they walk and feed. Grunting is typical of many large, group-living ungulates residing in open habitats, and it may help maintain group cohesion.

A notable behaviour of both sexes is wallowing. Bison paw shallow depressions in the ground and roll in them. Wallows are usually located in drier areas, and wallowing creates a dusty soil that the Bison seem to like. Wallows are scattered throughout their range and many are used over and over again until they are several metres in diameter. Outside the rutting season, wallowing probably has some grooming function, helping to shed the winter coat, and with the dust, helping to control biting flies.

Rutting males often utter challenging roars that can be heard from long distances. The roars are quite unlike the bellowing of male Domestic Cattle. Opponents approach each other head on, usually walking slowly, with tails raised (the raised tail is a sign of aggression in Bison and can be given towards humans). Two evenly matched males will stand facing each other performing nod threats, first with the heads turned to one side, and then quickly dropping and raising their heads in unison. Nod threats are sometimes repeated for several minutes. Lateral or broadside displays are also common: the displaying male stands four to eight metres away, at a right angle to his opponent. Males often roar during displays, and if the opponent moves, the displaying animal will walk in a slow, stiff-legged gait and stand in front of him again. Occasionally, both males will display laterally, standing parallel to each other. Male Bison also paw the ground, wallow briefly and rub nearby trees with their horns as preludes to further aggression. An animal signals submission by turning his head away, then moving away slowly.

If threats do not work, a fight usually results. The males face each other a few metres apart, then suddenly charge, butting heads with considerable force. The large mat of hair on the head probably helps cushion the impact, as does some minor pneumation of the skull. Males will also try to hook and gore each other along the sides with their short, sharp horns, occasionally with lethal results.

Bison are polygynous, and mating takes place usually between July and September. During the rut, a male seeks out a single female to court within a group. The mating unit is often referred to as a tending pair, because an adult male defends and courts only one female at a time. Male courtship is quite simple, the male stands close alongside the female while she grazes. Periodically, he checks her oestrous state by testing her urine and lip-curling. When she comes into oestrus, he stands at her rear, steps towards her, swings his chin towards the top of her rump, often making a soft panting sound. The female usually moves away from the male at this stage, as she does when he tries to mount her. Only when in full oestrus will the female allow the male to mount her, before immediately moving away. The male must usually copulate while walking or running on his hind legs. After a successful copulation, the female often arches her back, urinates and then holds her tail horizontally for four or more hours. Most females accept only a single copulation during each mating season.

Habitat


Bison in the province inhabit the Boreal Forest Region of northeastern British Columbia where the natural vegetation includes open Trembling Aspen or conifer forests, and shrub lands with extensive wet and dry open meadows. Such habitats may be more typical of the Wood Bison; Plains Bison are more at home in open grasslands, typical of the rolling short-grass prairies of North America.

Taxonomy


Despite many scientific papers on the subject, the subspecific distinctions between Wood and Plains Bisons are unresolved. Some researchers suggest that they are ecotypes; others maintain that they are distinct subspecies. Originally, they were separated by differences in cranial measurements, particularly those of the horn cores, but these secondary sex characteristics are notoriously variable and so are poor criteria for separating subspecies. Analysis to date shows that neither skull nor external characteristics hold consistently, nor does the analysis of blood or genetic parameters support a distinction between the two types. Having seen both types of Bison, live and in photographs, and having studied and measured many skulls, I found no consistent differences between them. There was a range of phenotypic variation, particularly in hair pattern, body colour and hump shape between and within the North American Bison populations that I examined. Another researcher recently re-evaluated the external characteristics he had used to distinguish Wood Bison. He concluded that they were probably the result of the founder effect because they were based on animals from a small, isolated population of Wood Bison held in the southern part of Elk Island National Park, Alberta. Despite these findings, some researchers still maintain that there is evidence for distinguishing these two races of Bison in North America.

The type locality for Plains Bison is in New Mexico, while that of Wood Bison is a site 80 km southwest of Fort Resolution in the Northwest Territories. Another living Bison species is the Wisent or European Bison, now restricted mainly to captive or park populations in Western Europe and Russia. This species is adapted to a forested habitat and is morphologically quite different from the North American Bison.

During the early Pleistocene, probably in Asia, Bison evolved from a common ancestor with Cattle, becoming adapted to open steppe grasslands, while Cattle evolved in open forests. These early Bison were originally similar in size to the modern species, but became larger in the middle of the Pleistocene; some of these larger animals lived in B.C. The horns of these large fossil forms were especially large – some spanned over two metres from tip to tip. There are several records of fossil Bison in B.C. They have been found on the Saanich Peninsula on southern Vancouver Island and on some nearby islands, at Babine Lake in the central interior, and in at least four sites around Fort St John. Dates for these fossils range from around 10,000 to over 30,000 years before the present. Remains of more recent Bison, usually skulls of adult males, turn up in passes through the Rocky Mountains (e.g., around Crowsnest Pass), and occasionally in archaeological sites in the Kootenay region. In 1793, explorers reported that Bison were numerous near the confluence of the Pine and Peace rivers in northeastern B.C.

Remarks


All free-ranging Bison in the province are the result of introductions and reintroductions either to B.C. or to neighbouring areas. The original animals for both the Wood and Plains Bison reintroductions into B.C. came from two herds in Elk Island National Park, Alberta, each originating from different sources. The Wood Bison originally came from northern Wood Buffalo National Park, and the Plains Bison from what was previously Wainwright Buffalo Park in southern Alberta, which in turn had originated from Bison from Montana.

Status Information

Scientific NameOrigin StatusProvincial StatusBC List
(Red Blue List)
COSEWIC
Bos bisonNativeS3No StatusNot Listed
Bos bison athabascaeNativeS2RedSC (Nov 2013)
BC Ministry of Environment: BC Species and Ecosystems Explorer--the authoritative source for conservation information in British Columbia.

Synonyms and Alternate Names

Bos bison Linnaeus, 1758

Additional Photo Sources

General References


Recommended citation: Author, Date. Page title. In Klinkenberg, Brian. (Editor) 2021. E-Fauna BC: Electronic Atlas of the Fauna of British Columbia [efauna.bc.ca]. Lab for Advanced Spatial Analysis, Department of Geography, University of British Columbia, Vancouver. [Accessed: 2022-01-25 6:43:17 AM]
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