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Barren-ground
Caribou
Herds
Until
the 1960s, barren-ground caribou herds were named based on where they
wintered. Most aerial surveys estimated herd size based on the number of
animals seen on late winter and spring migration ranges, even though the
location of these ranges varied
annually. Although calving
grounds were known, they were not routinely surveyed to estimate caribou
numbers until ear-tagging and field observations revealed that cows always
returned to their traditional calving grounds.
After that discovery, herds were named by the location of their
calving areas.
Research
in the 1990s provided evidence that barren-ground caribou belong to
discrete herds. First, the use of satellite collars revealed that cows that
calved together were also together during the rut (mating time). Second,
DNA analysis indicated that the herds were genetically distinct from each
other and probably have been for hundreds of years or longer.
Why caribou always return
to the same general area to calve is uncertain but their traditions have
held for hundreds of years. Referred to as the “traditional calving
grounds”, this is the cumulative area, overlapping from year to year,
that the cows return to annually for calving. Within these traditional
calving grounds, a trend in the use of different areas may become apparent
over time. For example, since the mid 1980s the Bathurst herd has calved
consistently further west each year so that in 1996 the herd calved
entirely west of Bathurst Inlet. Inuit
elders recollect the same thing happened in the 1950s.
Predation
by wolves and grizzly bears is the leading cause of caribou deaths.
Each wolf can kill 15-30 caribou per year. The number of wolves in
the ranges of the barren-ground caribou herds varies substantially over
time. When wolf numbers are high, wolf predation will help determine if a
herd increases or decreases. Recent studies have revealed that
barren-ground grizzly bears are also effective predators on caribou,
particularly in mid-summer prior to the ripening of berries on the tundra.
Weather conditions can also affect herd numbers.
Hot sunny summers can result in increased insect harassment and
reduce time available for foraging while cool windy summers will allow
caribou to maximize summer foraging time. Harsh winters can bring
exceptionally deep snow or ice, making it difficult for caribou to feed.
In the long run, forest fires maintain productivity of lichen ranges, but
in the short-term these fires may alter the winter distribution of the
herds, as caribou must search for available forage.
Changes in the herd’s winter distribution can also change the
availability of caribou to people who rely on caribou to meet their needs.
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