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bison can live up to 40 years. With the exception of humans, wolves
and bears are the main predators. The predators preferably attack
bison herds with calves. If a female is heavy and in good condition,
her offspring has an increased chance of survival.
bison live in groups of variable size and are usually at their largest
in the summer. Females tend to gather in larger groups so as to reduce
the chances of predation on their calves. Vigilance varies with group
size, where as the net vigilance (i.e. for the entire group) is increased
and the per capita vigilance (i.e. for each individual in the group)
is decreased in large groups.
bison populations, polygyny takes place and
sexual segregation occurs except when nutritional
or reproductive demands need to be met.
and foraging habits
bison are found throughout aspen and open boreal forests of north-western
Canada. They have a strong affinity for meadows, especially wet sedge
meadows which are used almost exclusively during winter. Females are
found to be more selective than males, preferring habitats with relatively
increased visibility and with presumed higher protein quality. Forage
availability is the main factor determining both habitat selection
and use, which explains the shifting of habitat at specific periods.
are primarily grazers and eat a wide variety of grasses and sedges.
They also feed on the leaves and bark of both trees and shrubs, such
as willows, as well as feeding upon lichens during the fall.
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bison versus plains bison
wood bison are taller and less stocky than plains bison. They lack
hair on their upper forelegs and have:
Larger body sizes
bison are currently considered as a subspecies of the North American
bison, but their taxonomic status is actually unclear and controversial.
Many studies have been done, yet none have lead to a clear and definitive
one point, van Zyll de Jong (1986) concluded that the phenotypic discontinuity
between grassland and woodland populations fully justified the recognition
of the two current subspecies of bison.
the other hand, Geist (1996) concluded that the
wood bison was a phantom subspecies. He found that wood bison transformed
miraculously into perfectly good "plains bison" when they
were removed from Elk Island National Park and put in captivity or
in the wild. He argues that wood bison is not a subspecies but rather
an ecotype reflecting environmental conditions
due to confinement and shortage of nutrients, stopping them from finishing
growing their hair coats.
et al. (1996) found a lack of monophyly in
bison. This suggests that the bison subspecies have only been recently
separated from each other, making it very difficult to have well-defined
taxa for each subspecies. Thus, defining the subspecies and detecting
hybridisation is less effective and hard to accomplish.
historical range of the wood bison in Canada covered north-eastern
British-Columbia, northern Alberta, north-western Saskatchewan, south-western
Northwest Territories, and the Yukon. Nowadays, its geographical range
is mainly reduced to small patches in Alberta, Manitoba, Yukon, and
south-western Northwest Territories, where small herds are surviving.
North American bison historical
Modified from van Zyll de Jong (1986)
Recent distribution of captive
and free-roaming herds of bison
Modified from van Zyll de Jong (1986)
status and conservation history
one point in Canada's history, it was estimated that approximately
168 000 bison were free-roaming. By the late 1800s, only about 250
wood bison were left, a considerable decline to which the introduction
of the firearm and the severity of numerous winters may have been
Protection started through legislation
Establishment of Wood Buffalo Park
Introduction of plains bison into the park
persons protested; they maintained inbreeding and diseases would
occur. Their protests were ignored and the introduction resulted
in hybridisation of the wood bison and transmission of tuberculosis
and brucellosis into the park.
Wood bison were thought to be extinct due to hybridisation
Wood Buffalo Park became a National Park
A small remnant herd was discovered in north-western Wood Buffalo
part of a recovery program in 1959, disease-free wood bison from this
herd were transferred to the Mackenzie Bison Sanctuary and Elk Island
National Park in order to establish breeding herds for captive breeding
and subsequent transplants. In 1975, a cooperative recovery program
was initiated with the objective of re-establishing free-roaming non-diseased
herds of wood bison.
efforts increased the population number of free-roaming wood bison
from 200 to approximately 3000 in 1999. The latest count of non-diseased
wood bison is 3536, of which 2828 are found in the wild and 708 in
captivity. Six populations are found in the wild but only two exceed
the minimum number for a viable population of 400 individuals. Four
captive breeding herds are also present and are kept for the preservation
of gene pools.
threats and problems
of crossbreeding and contracting diseases
populations of wood bison in Canada are now believed to be disease-free
apart from those from Wood Buffalo National Park. The increasing number
of wood bison in each of the various populations leads to an increase
of required area. Obviously, this increases chances for disease-free
wood bison to be in contact with diseased bison from Wood Buffalo
National Park and for crossbreeding with other bison (i.e. hybrids
and plains bison).
bodied mammals are especially vulnerable to effects of habitat fragmentation
because they require lot of space. Their vulnerability is mainly a
consequence of the isolation of small populations. This increases
the level of inbreeding, as relatives are forced to mate with one
another. When the species is characterised by polygyny, as with bison
populations, only a few dominant individuals may be responsible for
most offspring, leading to a further increase in the mean relatedness
of the population.
most bison are found in small heavily managed populations, the main
pressing management problems include isolation and restriction to
small tracks of land. These problems result in rapid population increases
and require subsequent culling. Thus, the elimination of unhealthy
and/or hybrid bison is required to release healthy wood bison populations
throughout their original range and keep the genetic diversity.
try to solve the problems, a study was performed to refine techniques
for the development of assisted reproductive technologies in the form
of embryo collection and transfer, as well as to evaluate animal responses
to these techniques. The advancement of this technology could help
ensure the long-term propagation and the genetic management of wood
bison by improving captive propagation efficiency and maintaining
human development & bison
1985, Canadian cattle were declared free of brucellosis and almost
free of tuberculosis. The bison of the Wood Buffalo National Park
were and are still the last remaining focus of both diseases. Since
agricultural activities had become closer to bison ranges as a result
of the gradually increasing needs of human populations, the diseases
were and are still a real concern for cattle.
consequence of the expansion of agricultural and human developments
is a major loss of bison habitat, restricting bison to smaller ranges
and diminishing food availability.
range size of bison is determined by forage requirements. When an
area has a higher food accessibility (i.e. having larger, more abundant,
and closer food patches), home ranges are smaller. In larger groups,
since less food is available per individual in a given area, larger
home ranges are required. As wood bison populations are expanding,
bison are being restricted to small isolated areas, as well as being
threatened by habitat loss and fragmentation, which leads to a decline
in food availability. These factors necessitate an increase of the
size of bison's home range, a concern with regards to bison conservation.
recent developments in the conservation of wood bison
Federal Environmental Assessment Review Office investigated several
possible options in 1990. They concluded that the best one was to
eliminate infected hybrid populations and to repopulate them with
disease-free wood bison.
of the option
such a controversial option was given, an independent assessment of
the effects of tuberculosis and brucellosis on wood bison demography
was performed. The results have shown that:
Both diseases were prevalent in older animals but tuberculosis
was more prevalent in males than in females.
Both diseases were not a function of bison density.
diseases affected pregnancy rates; diseased populations had a
significantly lower calf:cow ratio than healthy populations.
diseases affected the annual survival rate; the mortality rate
of diseased bison was 2.5 to 3.7 times higher than that of healthy
it was shown that two factors, disease and wolf predation, were required
to happen simultaneously to result in a significant population decline.
When only one factor was present, populations seemed to be more or
the light of these results, it was concluded that the ongoing presence
of two economically important diseases in northern Canada results
in a conflict with respect to further bison recovery. The only way
to effectively eradicate the diseases involves depopulating and repopulating,
as it was suggested in 1990 by the Federal Environmental Assessment
Review Office. On one hand, it brings the social concern that the
disease management is too drastic and an unnecessary intrusion into
the policies of a National Park. On the other hand, these diseases
prevent the reintroduction of a keystone species throughout its former
range in northern Canada, forty percent of this range being evaluated
to be available and suitable for reintroduction. In addition, the
Mackenzie Bison Sanctuary contains approximately 2000 disease-free
wood bison and the migration of diseased bison presents a quantifiable
risk of transmitting the diseases to healthy populations.
the need for reintroduction of bison was expressed in another study.
As a conservation strategy, it was mentioned that reintroduction of
bison into several independent sites of their historical range would
facilitate re-colonisation and achieve a faster spread than a reintroduction
into a single site and waiting for the population to spread as a result
of its own density dependent responses.
conclude, whether or not wood bison are a subspecies, a host of environmental
and human factors contributed to their destruction and finding a clear
solution for a successful comeback is not that easy. The solution
to this problem needs a clear consensus on the long term recovery
goals of this species and a transparent evaluation of whether short
term costs of disease management are justified in relation to these
ranching is not conservation, it is domestication!
We should therefore concentrate our conservation efforts toward free-roaming
wood bison populations and apply the best solution for their reintroduction
to their former range.
find the best management solution for wood bison conservation, more
advanced research on the following subjects would be useful:
Genetic and taxonomic identities
and nutritional requirements
problems of captive herds
management and study of larger species is hard because of the long
generation time. However, the study of larger species more readily
stimulates public awareness and education, which hopefully might greatly
contribute to the preservation of the wood bison in the future.
Wildlife Service (CWS)
Recovery of Nationally Endangered Wildlife (RENEW)
J. and C. Cunningham. 1994. Bison: Mating and conservation in small
populations. Columbia University Press, New York.
L. N. and T. Trottier. 1987. Responses of bison on their calving grounds
to predation by wolves in Wood Buffalo National Park. Can. J. Zool.
Environmental Assessment Review Office. 1990. Northern diseased bison.
Report of the Environmental Assessment Panel, Hull, Canada.
V. 1996. Buffalo nation: History and legend of the North American
bison. Voyageur Press, Stillwater, Minnesota.
A.C. 2000. The destruction of the bison: An environmental history,
1750-1920. Cambridge University Press, New York.
P. E., F. Messier and C. C. Gates. 1993. Group structure in wood bison:
nutritional and reproductive determinants. Can. J. Zool. 71: 1367-1371.
N. C. and C. C. Gates. 1990. Home ranges of wood bison in an expanding
population. Journal of Mammalogy 71(4): 604-607.
N. C. and C. C. Gates. 1991. Diet and habitat selection of wood bison
in relation to seasonal changes in forage quantity and quality. Can.
J. Zool. 69: 2677-2685.
N. C. and C. C. Gates. 1994. Home-range size of wood bison: Effects
of age, sex, and forage availability. Journal of Mammalogy 75(1):
N. C., A. R. E. Sinclair, T. Ellsworth, J. Nishi and C. C. Gates.
2000. Dynamics of reintroduction in an indigenous large ungulate:
the wood bison of northern Canada. Animal Conservation 3(4): 299-309.
L. S., A. C. Bellem, C. J. Gartley, K. Auckland, W. A. King, R. M.
Liptrap and K. L. Goodrowe. 1999. Hormonal control of estrous cyclicity
and attempted superovulation in wood bison (Bison bison athabascae).
Theriogenology 52: 313-323.
R.O., R. Beech, J. Sheraton and C. Strobeck. 1996. Genetic relationships
among North American bison populations. Can. J. Zool. 74: 738-749.
S. V., C. C. Gates and L. B. Forbes. 1993. The brucellosis and tuberculosis
status of wood bison in the Mackenzie Bison Sanctuary, Northwest Territories,
Canada. Can. J. Vet. Res. 57: 231-235.
Wood Bison Recovery Team. 1987. Status report on wood bison (Bison
bison athabascae) in Canada, 1987.
Zyll de Jong, C.G. 1986. A systematic study of recent bison, with
particular consideration of the wood bison (Bison bison athabascae,
Rhoads 1898). National Museums of Canada, Ottawa.
reproduction, all the females of a given population give birth approximately
at the same time.
polygynous ungulates such as the bison, sexes form separate groups
and are spatially segregated for most of the year.
where individual males may mate with more than one female per breeding
smallest taxonomic subdivision of an ecospecies, consisting of populations
adapted to a particular set of environmental conditions.
taxonomic species considered in terms of its ecological characteristics
and usually including several interbreeding ecotypes.
a group or taxon that consists of an ancestor and its descendants.
that results from infection with the bacterium Mycobacterium bovis
and is characterised by the formation of tubercles on the lungs and
other tissues of the body, often developing long after the initial
infection. The disease is contagious. Infected animals pass bacteria
in their secretions and excretions. It may spread from infected to
uninfected animals through inhalation of droplets expelled by coughing
animals, by ingestion of food or water contaminated with the bacterium
by infected animals, or from mother to offspring either through the
placenta or contaminated milk.
disease is progressively debilitating and can affect the respiratory,
digestive, urinary, nervous, skeletal, and reproductive systems. It
can weaken animals and make them more susceptible to predator, it
can reduce fertility in sexually mature animals, and in advanced cases,
it can be fatal.
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caused by infection with the bacterium Brucella abortus. It
is characterised by involvement of the reproductive organs resulting
in abortion, infertility, and uterine infection in females and inflammation
of the testes in males. Calves born alive from infected females can
be weak and die soon after birth. It can also invade joints, causing
by exposure to aborted fetuses, fluids passed from pregnant uteri,
infected new born calves, or by consumption of food or water contaminated
by these materials. Calves can be infected by ingestion of their mother
milk. Infected males can transmit the disease through contaminated
semen at breeding time.