Wood Bison in the NWT
Wood bison, (Bison bison athabascae), northern cousins of the plains bison (Bison bison bison), are North America's largest land mammals. In Dogrib, bison are called Dechita goji / enareh goji and in North Slavey they are ?ejire.
For more information on wood bison and their recovery, see the Wood Bison Management Strategy for the Northwest Territories, 2010-2020.
Wood bison are found in four areas of the NWT:
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- Mackenzie Bison Population: This is the world's largest free-ranging herd of disease-free wood bison.
- Liard River Valley: These disease-free bison range through the Liard River Valley and have expanded their movements into British Columbia and the Yukon.
- Slave River Lowlands: Two herds in this area include the Little Buffalo herd on the west side of the Slave River and the Hook Lake herd on the east side. Both are infected with bovine tuberculosis and brucellosis.
- Wood Buffalo National Park: Established in 1922, this park was established to save the wood bison from extinction. All wood bison within the park are infected with bovine tuberculosis and brucellosis.
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The Bison Control Area, an area which is free of bison, was established to lower the risk of diseased herds coming in contact with healthy herds.
Wood Bison in the NWT are classified as Threatened. Read more: Species at Risk Fact Sheet - Wood Bison
Description
The wood bison is the largest native terrestrial mammal in North America. They are generally taller and less stocky than plains bison. At maturity wood bison bulls measure over 1.8 m at the shoulder and weigh over 1000 kg. Cows are smaller, averaging 550 kg. The wood bison is larger than the plains bison, has a more pronounced hump and has less hair on the front legs and throat. Bison have a woolly undercoat overlain by longer guard hairs, which makes them resistant to cold temperatures. The beard tends to be less developed in wood bison than in plains bison. Male and female bison have short black horns extending upwards from the sides of the head.
The sex of a bison can be determined from the shape and size of its horns. The male's horns have a thicker base than the female's. In females the horns tend to be slender and commonly show a slight backwards recurve near the ends.
Classifying Bison Using Horn Shape and Size
Calves: Young of the year of both sexes. Calves are typically born in April-May, with calving largely completed by early July. At birth, calves have reddish-tan coats which turn dark chocolate brown by about 3 months of age.
Yearlings: Animals of both sexes with spike-shaped horns (10-30 cm length).
Cows: Horns are thinner than those of any male. Horns are curved toward the middle line of the skull or towards the back forming an S-shape in older cows. Front of the skull is narrower than that of adult bulls.
Juvenile Bulls: Base of horns is wider than cows. Horns point upward or outwards, but are never curved to point towards each other.
Sub-adult Bulls: Hair on head and shoulders is shorter than in adult bulls. Horns point straight up or towards the middle line of the skull. Base of horns is wider than in cows.
Adult Bulls: Body size is much larger than cows. Hair on chest and head is fully developed, leaving no open space between the horns. Horns are curved towards the middle line of the skull. Older bulls can be identified by their worn horn tips.
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History
When the earliest European explorers arrived in western Canada in the mid-17th century, an estimated 2,000,000 plains bison (Bison bison bison) ranged over the Canadian prairies. One hundred and fifty years later, the vast herds that once dominated the open landscapes had been reduced by excessive slaughter to a few scattered survivors.
In the boreal forest to the north the wood bison (Bison bison athabascae) suffered a similar fate. In the mid-17th century, it was estimated that 168,000 were scattered unevenly throughout a vast area in northern Alberta, north-eastern British Columbia, southern Yukon, the interior of Alaska and the south-western Northwest Territories. The decline of the wood bison in Canada's North coincided with the rapid demise of bison on the prairies between 1800 and 1870. By 1875 the wood bison had disappeared from much of its historic range. In 1891, only 250 remained in the wilderness area between Great Slave Lake and the Sweet Grass area. The cause of the decline is poorly documented, but records from trading posts and Northwest Mounted Police files suggest that heavy hunting following the introduction of firearms into the region was an important contributing factor. Bison were hunted as a source of meat for supplying trading posts and for making high quality pemmican to nourish voyageurs.
Conservation efforts for bison began in Canada in 1877 when the Buffalo Protection Act was passed. However, this legislation was largely ineffective because of a lack of enforcement. With the establishment of a Northwest Mounted Police post at Fort Fitzgerald on the Slave River in 1907, the wood bison began to recover. In 1922, Wood Buffalo National Park was established to provide further protection for the wood bison and its habitat.
In 1906, the Canadian Government purchased 709 plains bison from an American rancher in Montana. These bison were shipped to Elk Island National Park and were later transferred to Buffalo Park near Wainwright, Alberta. The protected bison thrived and in 1925-28, 6,673 plains bison were transferred from Buffalo Park to the newly established Wood Buffalo National Park on the Northwest Territories/Alberta border. About 400 of the transplanted bison rapidly migrated to the lush Sweet Grass area. To protect those animals, the park was enlarged to its present size of 44,980 km2 .
The transplanted plains bison outnumbered the resident wood bison by about four to one and the two subspecies readily interbred. By 1934 the herd had increased to about 12,000 animals. The Wood Buffalo National Park transplant had two unfortunate consequences. Firstly, it was thought that the wood bison as a distinct subspecies had been lost. Secondly, the transplant introduced two cattle diseases, bovine tuberculosis and brucellosis, into an area where they had been previously absent.
It was believed that a small population of wood bison persisted in the remote northern reaches of Wood Buffalo National Park that had not interbred with the plains bison. In 1959, five specimens were collected from a herd of about 200 animals in the Needle Lake area and they were classified as wood bison. Recent studies have shown that some other subpopulations in the Wood Buffalo Park area also closely resemble the original wood bison more than the plains bison.
In 1963, wood bison were captured from the Needle Lake area of Wood Buffalo National Park to establish a captive breeding herd. After testing for diseases, 18 bison were transported to an unoccupied area of historic range a hundred kilometres away on the west side of Great Slave Lake. These animals have since given rise to Canada's largest contiguous free-roaming herd of bison and the largest population of healthy wood bison.
A second round-up of wood bison was held in northern Wood Buffalo National Park in 1965. Twenty-one animals were successfully transferred to Elk Island National Park in central Alberta. These translocated animals carried both bovine tuberculosis and brucellosis, but through a rigorous management protocol involving isolation and quarantine of neonates and elimination of original stock, these diseases were eradicated. This disease-free breeding herd provides founding stock for captive zoo and park herds, breeding ranches and for reintroducing free-ranging populations.
Distribution
Wood bison are found in four areas of the NWT:
Behaviour
Wood bison are gregarious and form mixed groups of cows, calves, yearlings, and sub-adults. Mature bulls are usually solitary or form small groups of their own, joining the cow herds during the breeding season.
The herds are wary and are sensitive to disturbance. Bison have a keen sense of smell, but limited vision. While they can detect movement a kilometre away, they might walk past a person sitting quietly at the edge of the forest. In hunted populations, cow / juvenile groups react strongly to the sound of a snow machine and might run 5 km or more. When frightened, these normally slow plodding animals can break into a rocking gallop, attaining a top speed of 60 kilometres per hour.
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The onset of fly season in summer agitates the bison. Their sensitive eyes, nostrils, and almost hairless flanks are plagued by hordes of blackflies and mosquitoes. On hot summer days, huge "bull dog" horseflies bite their sensitive legs and thighs. High wind provides some relief from flies and bison also combat these pests by rolling in dust wallows. Wallowing also serves as a social display for bulls, advertising their great size to possible competitors or intruders. |
Bison are grazers, feeding on grasses and sedges that grow in meadow openings. Willow leaves and twigs are an important part of the early summer diet, providing a rich source of protein and other nutrients. Bison use a variety of habitats during the year but rely heavily on grasses and sedges at all times, particularly in the winter. Bison forage in deep snow by using their heads as a snowplough, pushing snow aside with powerful side-to-side sweeping movements.
Reproduction
The breeding season occurs from mid-July to late September, with the peak rutting period in early August. Bulls are generally found in their own groups before the rut and enter the mixed herds when cows come into oestrus. Dominance among bulls is established by behavioural display, sparring matches, and occasionally by violent fighting between evenly matched bulls. With an upraised tail, a bull will usually give aggressive signals such as head-bobbing, snorting, wallowing, and pawing. The roar of a rutting bull can be heard up to a kilometre away.
Sexual maturity is attained at 2 to 3 years of age for both males and females, and while females usually produce their first calf at age 3, males generally do not breed until they are at least 7 or 8 years of age. Younger bulls are capable of breeding but are prevented from doing so by older males.
| Cows give birth from April until July, but the peak of calving occurs in May. One calf is usual and twins are extremely rare. At birth, calves have reddish-tan coats which turn dark chocolate brown by about 3 months of age. They nurse soon after birth, balancing on long spindly legs, and within the same day can be seen bucking and running about. Cows recognize their own calves by smell and chase away strange calves. Although calves nibble on grass within a few days of birth, they continue to nurse for 7 months or longer, gradually increasing forage intake until they rely entirely on an adult diet of grasses, sedges, and other plant matter. Mortality can be high during the first year. Young calves use up their limited fat reserves during the long cold winter, and are not efficient at foraging or avoiding predators, particularly wolves. |
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Mortality
Predators
In the NWT, timber wolves are the most significant predators of bison. Calves and injured or diseased animals most often fall prey, but occasionally wolves will attack healthy adult bison. Wolf predation can seriously affect calf survival and herd numbers, especially if the bison population has been affected by other factors.
Bison herds in the Slave River Lowlands and Wood Buffalo National Park are a case in point. Calf production is poor, compared with non-infected herds, and, wolf predation is high. Weakened by disease, many adults fall prey to wolves. The wolves, in turn, prosper and produce large healthy litters. As the pups grow up and hunt more bison, the bison population reaches a point where births no longer exceed deaths. When a herd is pushed to this limit, it declines until only a few bison are left and wolves become limited by their ability to find prey.
Disease
Three major bacterial diseases affect wild bison: brucellosis, bovine tuberculosis, and anthrax. Brucellosis and tuberculosis were introduced to Wood Buffalo National Park with the transplant of plains bison from Wainwright, Alberta in 1925-28. Both diseases are prevalent in bison in the park and in the Slave River Lowlands. Brucellosis causes abortions, still births, lower pregnancy rates, and can cause crippling arthritis in infected joints. The infection is transmitted primarily through contact with contaminated fluids or tissues associated with abortions or birth. Males may acquire brucellosis through sexual contact with infected females. Bovine tuberculosis is a chronic, infectious disease that usually progresses slowly in bison. Over the years it weakens the bison and may eventually result in death. These two diseases increase the vulnerability of bison to wolf predation.
Anthrax is the other serious disease affecting bison in the NWT. During the first documented outbreak of anthrax, in the summer of 1962, 281 bison died near Hook Lake, in the eastern Slave River Lowlands. Outbreaks soon became widespread, extending during the course of the next few years to as far south as bison herds in the Sweet Grass area. In 1965, an anthrax vaccination program was initiated. Vaccinations were carried out in late winter or spring, before the time when anthrax usually occurred. The vaccination program was hard on the bison. Constant human activity and herding by helicopters and other vehicles caused extreme harassment. Many bison died from exhaustion and panic. The program continued intermittently from 1965 to 1977 resulting in close to 20,000 vaccinations. The effectiveness of the vaccination program was poorly documented.
An outbreak of anthrax in the isolated Mackenzie herd in 1993, 30 years after bison were introduced to the Fort Providence area, leads to the question, "Where does anthrax come from?". Anthrax is found in the soil as a dormant, highly resistant endospore. It survives best in basic or alkaline, calcium-rich soils, such as those found in the most productive bison ranges in the Northwest Territories. The spores can remain viable and infectious for decades if not hundreds of years. When water levels recede after a period of flooding, the spores that have been washed out of the soil become concentrated in pockets. Herbivores like moose or bison become infected by ingesting or inhaling the spores.
Infected animals become sick and die within four days and few recover. Anthrax spores are formed again when carcasses are opened by scavengers and anthrax organisms are exposed to the air. Scavengers like the raven are not affected by anthrax and can transport spores over long distances. Since the disease can be lethal in humans if untreated, anthrax outbreaks are treated very seriously. Bison herds are closely monitored during anthrax season (June to August) and contaminated carcasses are incinerated as soon as possible.
For more information on wildlife diseases, please click here.
Accidents
Drowning is a frequent cause of death in bison. Although they are normally excellent swimmers, entire herds of bison have drowned in flooded rivers. In 1958, spring floods in the Sweet Grass area in Wood Buffalo National Park, caused the death of about 500 bison. In 1959, more than 1,000 animals died during autumn flooding. In both 1961 and 1974, several thousand bison drowned in the same area. In May 1989, 177 bison died in the Mackenzie bison range when they broke through rotten spring ice. Catastrophes do not affect long term trends in large bison populations, but they can cause the extinction of small local populations.
Hunting
Between 1968 and 1977, resident sport hunters took an average of 123 bison per year during regulated seasons in the Slave River Lowlands. At the same time, hunting by General Hunting Licence (GHL) holders had no season or quota limit. Between 1973 and 1976, the bison population declined and sport hunting was closed in 1977, but GHL hunting has remained unregulated.
Regulated hunting for male bison was allowed for the Mackenzie bison herd beginning in 1988. The quota is divided between Fort Providence, Rae-Edzo, and an open draw for eligible hunters from the NWT. Fort Providence provides outfitting and guiding services for a limited number of non-resident bison hunters.
A quota was first implemented for the Liard River herd in 1998. The quota was set at 2 animals, 1 each for the communities of Fort Liard and Nahanni Butte, however, no tags were utilized until the 2002/03 season.
Hunting is not permitted in Wood Buffalo National Park.
Population Status in the NWT