Description

Wood bison, northern cousins of the plains bison, are North America's largest land mammals.  They can be recognized by their huge heads, large shoulder humps and shaggy brown fur on their shoulders and front legs.  Both sexes have short black horns.  Females have straight horns while male horns curve slightly inward.  Males are larger than females and can reach 3.8 metres in length and more than 1.8 metres in height.  Wood bison are massive creatures ranging in weight from 550 -1000 kilograms.

Distribution

Historically, wood bison ranged throughout the boreal forest of northern Alberta, northeastern British Columbia, southwestern NWT, the Yukon and central Alaska.  Today, the majority of free-roaming wood bison populations are found in the NWT.  They currently reside in several herds:  the Mackenzie herd east of Great Slave Lake; the Nahanni herd in the Liard Valley between Fort Liard and Nahanni Butte and extending south into British Columbia; the Hook Lake and Little Buffalo herds in the Slave River lowlands; and, several herds in Wood Buffalo National Park.

NOTE: Click on map for full view. Distributions are approximate and not intended for legal use. (JPG = 692 KB)

Population Size and Trends

Never as common as the plains bison, the wood bison population was estimated at 168,000 animals in 1800.  Wood bison were hunted almost to extinction during the 19^th century.  By 1893, the population had declined to an estimated low of 250 animals.  Numbers slowly increased and had reached 1500 to 2000 by 1922.  At that time, Wood Buffalo National Park (WBNP) was established in an attempt to save wood bison from extinction and to protect its habitat.

From 1925 to 1928, 6,673 plains bison were transferred from Wainwright Buffalo Park in central Alberta to WBNP.  Unfortunately the introduced bison were infected with bovine brucellosis and tuberculosis.

By 1940, it was feared that wood bison had disappeared as a subspecies as a result of interbreeding with plains bison.  However, in 1957 federal wildlife officials discovered a herd of pure wood bison in the Nyarling River area of the park.  In 1963, 18 animals were captured and released in the Mackenzie Bison Sanctuary.  These animals founded the Mackenzie herd, which grew to about 2,400 by 1989 and stabilized at 1900 animals by 1998.  The Mackenzie herd is now the world’s largest free-ranging herd of disease-free wood bison.

Another 21 wood bison were captured in 1965 and released in Elk Island National Park.  The Elk Island herd was used to form the Nahanni herd, which now numbers 160 animals.  The Hook Lake and Little Buffalo herds (Slave River Lowlands) have not done as well.  Their combined populations have dropped from about 2,500 in 1970 to a current population of 500 to 600 animals.  The total bison population in Wood Buffalo National Park was estimated at about 4000 animals in 2002.

Wood bison use different habitats depending on the season.  In summer, they can be found in small willow pastures and uplands where they feed on sedges, forbes and willows.  In winter, they move to frozen wet sedge meadows and lakeshores where they feed on sedges.  In the fall, they can be found in the forest where they feed on lichens.

Bison are social animals and can be found in small herds throughout the year. Both males and females become sexually mature around two or three years of age.  Females usually have their first calf at three years of age but competition prevents males from mating until they are seven to eight years old.  Calves are weaned after seven months.  Females usually have two calves in a three-year period.

The main factor limiting recovery of the wood bison in the NWT is disease.  Tuberculosis and brucellosis were introduced into WBNP with the plains bison in the 1920s.  These two diseases, along with anthrax, are common in the herds in Wood Buffalo National Park and the Slave River lowlands.  Recent studies by the University of Saskatchewan suggest that disease levels in the park bison have not declined in the last 40 years for either brucellosis or tuberculosis.  In the most recent survey, 29 per cent of bison tested positive for brucellosis while 51 per cent tested positive for tuberculosis.  Both brucellosis and tuberculosis may make bison more vulnerable to predation.  Eliminating these diseases would remove the greatest obstacle to recovery.  Drowning in spring floods is also a problem faced by all herds in the NWT.  As many as 1000 animals can die in a short time when the spring ice cracks.

The first legislation to protect bison in Canada was passed in 1877.  In 1964, wood bison were declared a "protected species" under the Northwest Territories Act allowing for management and restriction of all hunting.  In 1977, COSEWIC designated wood bison as Endangered.  Population increases over the following decade resulted in COSEWIC down listing wood bison to Threatened in 1988.  The status was again revisited by COSEWIC in 2000, and they were confirmed as Threatened. Wood bison was legally listed as Threatened under the federal Species At Risk Act  in June 2004.

A National Recovery Plan to protect and recover the wood bison was completed in 2001.  A review and update of the Plan to conform with SARA requirements is expected to be ready in 2007.

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       Site last updated Tuesday, February 19, 2008