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Woodland Caribou

CaribouCaribou (Rangifer larandus) are currently found in all Canadian provinces and territories except Prince Edward Island, Nova Scotia and New Brunswick. The woodland subspecies is distributed across the forested and mountainous regions of Canada, including northern and west-central Alberta. The boreal and southern mountain populations of Woodland Caribou are considered threatened by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC 2000). Woodland Caribou are on Alberta's Blue List of species that may be at risk of declining to non-viable population levels in the province and are designated as threatened under the provincial Wildlife Act. Considerable research has been done on caribou ecology in Alberta over the past 20 years. Ecotypes are frequently used in the description of caribou because of the tremendous variation in behavior, habitat use patterns, or morphology of caribou from different regions. Woodland Caribou that live year round in forested habitat will be referred to here as boreal ecotype, while caribou that winter in forested foothills and migrate to alpine mountain habitat during summer will be referred to as mountain ecotype.

Woodland Caribou food -lichensWoodland Caribou typically rely on large tracts of mature to old forests that contain the caribou's primary winter food - lichens. Habitat use by the two Woodland Caribou ecotypes in Alberta contrasts most during spring, summer and fall. The migratory nature of most mountain caribou inhabiting Alberta's eastern slopes takes them from high elevation alpine habitats in spring, summer and fall to foothills forests in the winter. Boreal ecotype caribou inhabiting forests of northern Alberta make extensive movements throughout the year but most do not make predictable migrations and therefore habitat use does not differ on a seasonal basis. Lichens are an important food source for caribou and thus influence habitat use and distribution. Due to their extremely slow growth and limited dispersal mechanisms, lichens are found primarily in old forests. This fact contributes to the affinity of Woodland Caribou to relatively old forests. Alberta's boreal ecotype caribou are typically found in peatland (muskeg) complexes dominated by black spruce and larch. Habitat selection by migratory mountain caribou changes seasonally. The breeding season, or rut, typically takes place in alpine or sub alpine meadows. In winter, mature and old lodge pole pine or mixed pine/spruce/fir forests are most commonly used. Mountain caribou in some ranges now reside in the mountains year round, but move from low elevation winter ranges to upper sub alpine and alpine habitats in the summer. 

Caribou migrationRelative safety from predation is a key feature of habitat used by Woodland Caribou. The susceptibility of caribou to wolf predation has led to patterns of habitat use that separate them from other ungulates that cohabit the same geographic areas. For mountain caribou, this spatial separation occurs when they occupy different winter habitat than other ungulates and/or when mountain caribou make migrations to calve at higher elevations than moose, deer or elk.

Boreal caribou in Alberta do not migrate, however this ecotype separates itself from other ungulates by occupying habitat that has a lower density of other ungulate species year-round. The availability of extensive range 'space' is thought to be an important habitat characteristic that allows caribou to avoid predation. 

Caribou are medium-sized members of the deer family. They are distinguished by their brown pelage, cream-coloured neck and mane, and large, intricate, forward curving antlers. Males and most females have antlers, although the females' are smaller. Caribou are well adapted to harsh winter conditions. Their large, crescent shaped hooves and relatively long legs are useful for digging through snow, to reach their winter food, and provide effective weight distribution for locomotion over snow or muskeg. Other adaptations to winter conditions include short ears, short tail, and hollow hair that provides excellent insulation and covers the entire body including the muzzle. To further reduce heat loss, caribou have a slower metabolism and a reduced rate of movement in most late winters when deep, crusted snow makes travel energetically expensive. Despite these adaptations, fat reserves accumulated in summer are depleted during winter. Mountain and boreal ecotype Woodland Caribou differ in their seasonal movement patterns. Most mountain caribou in Alberta are migratory and make seasonal migrations between alpine or sub-alpine summer range and forested foothills winter range. 

Boreal ecotype animals wander extensively throughout the year but typically show considerable overlap between winter and summer ranges. By November, mountain ecotype animals begin to move to their wintering range, while boreal ecotype caribou disperse into smaller groups. 

Caribou calvesIn addition to predation, mortality factors for calves also include starvation, inclement weather, and reduced size at birth after hard winters.  In Alberta, terrestrial lichens constitute the bulk of the Woodland Caribou's winter diet. By exploiting a food source not normally sought by other ungulates, Woodland Caribou can spatially separate themselves from other species to reduce predation risk. Arboreal lichens (those growing on trees) are important food items in the diet of some caribou populations, especially those inhabiting mountainous areas with deep snow. Caribou in Alberta and Saskatchewan occasionally feed on arboreal lichens, and this food source may be most important when deep or crusted snow makes accessing terrestrial lichens difficult. The summer diet of Caribou is much more varied, including terrestrial lichens, shrubs, grasses sedges, horsetails, and forbs.

Reprinted from Alberta Wildlife Status Report No. 30 (2001), with permission from Alberta Sustainable Resource Development

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