Woodland caribou population dynamics in Northeastern Alberta

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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.

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