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Woodland caribou population dynamics in Northeastern Alberta
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- Author(s) / Creator(s)
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Studies of woodland caribou (Rangifer tarandus caribou) in the Birch Mountains of northeastern
Alberta were conducted from January 1976 through June 1978. Twenty-nine caribou were radio
collared and repeatedly located from fixed wing aircraft. Eight capture-related deaths were
associated with increased stress (hazing and handling time) and slow or incomplete absorption of
the immobilizing drug. Young bulls (1.0 to 3.0 years old) and adult, cows (>3.0 years old) were
sometimes indistinguishable from the air due to similar body size and antler morphology. Time
of antler drop among bulls was related to age. A population survey combining fixed-wing
transect flights and helicopter tracking over 1400 km2 yielded a late-winter density of
1 caribou/24km2. Radio-tracking data indicated that adult bulls concentrated in this area in
winter; adjusted resident density was 1/33 km2. The total caribou population on the 25 000 km2
Alberta Oil Sands Environmental Research Program study area was estimated at 433. Bulls
comprised 42% of animals older than calves. Calves made up 12% of the total fall and winter
population. Yearlings comprised 14% of captured caribou, but individuals born from 1972 to
1974 comprised only 15%. This apparently reflected low survival of animals born following
winters of deep snow and high food-short lynx (Lynx canadensis) populations. Calving occurred
from 7 May to 3 June. The pregnancy rate of adult cows (>3.0 years) was 88%. Calf survival was
42% in the first 2 months of life and 17% annually. Annual survival of radio collared adults
averaged 85%. At least two of four radio collared adults which died were killed by wolves
(Canis lupus). The calculated finite rate of population growth (A = 0.85) indicated a declining
population in years with normal snowfall. Radio collared adult bulls remained solitary in
summer, as did cows with calves. Both adult bulls and cows formed mixed groups during the rut
in September. Groups of adult bulls remained separated from mixed groups of cows and young
bulls in winter. Caribou group sizes were smallest in summer (mean: 1.2) and largest in late fall
after the rut (mean: 5.4). Continuous associations of radio collared caribou were longest in late
winter. Seasonal ranges and movement patterns varied greatly between individuals, but seemed
traditional among adult bulls. The latter made long-distance movements (>11 km) up to five
times per year to distinct seasonal ranges. Most cows moved two and sometimes three times per
year. The time of such movements by either sex was similar in all years. Seasonal range sizes
were similar for bulls and cows, though individual cows were much more sedentary and their
seasonal ranges overlapped much more. More annual range size of adult bulls was 1196 km2 and
that of cows was 539 km2. Seasonal changes in relative use of habitat types seemed related to
availability of food resources, snow depths, and social behaviour. Most locations (69%) were in
lowland cover, predominantly black spruce (Picea mariana) muskegs. Caribou used upland
deciduous cover types very little in any season. The great variability in winter habitat use
reflected habitat availability within individual winter ranges. -
- Date created
- 1980-01-01
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- Type of Item
- Report
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- License
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