Caribou, known scientifically as Rangifer tarandus, are a species of large deer that thrive across the northern reaches of the globe. These iconic mammals make their primary home in the Arctic and sub-Arctic tundra regions of North America and Eurasia. They are uniquely equipped to handle the extreme conditions of this environment.
The Tundra Biome: Caribou Habitat
The tundra represents a massive, treeless plain defined by permanently frozen ground known as permafrost, low average temperatures, and a very short growing season. Caribou utilize two distinct types of this habitat across their wide geographic range. The Arctic Tundra is a high-latitude biome that covers vast stretches of the far north, offering open space and specific vegetation that supports their massive herds. The other important habitat is the Alpine Tundra, which is found at high altitudes on mountain slopes, even at lower latitudes. Both types of tundra provide the open environment caribou herds need to maneuver and find forage, even though the plant life is sparse and low-growing.
Specialized Survival: Physical and Behavioral Adaptations
The survival of the caribou in the intense cold is largely due to their specialized physical traits, beginning with their extremely warm coat. They possess a thick, insulating double layer of fur, featuring a fine under-fur and an outer coat of longer, hollow guard hairs. Air trapped inside these hollow hairs provides excellent insulation, effectively conserving body heat in frigid temperatures. Their large, crescent-shaped hooves are another adaptation, acting like snowshoes to distribute the caribou’s weight across snow and soft, marshy ground. The sharp edges of the hooves also function as shovels, which the caribou use for digging through packed snow to reach food, a behavior known as “cratering”.
The Necessity of Movement: Seasonal Migrations
Caribou cannot survive in one location year-round and must undertake some of the longest land migrations of any mammal, traveling thousands of miles annually. This movement is a behavioral strategy that ensures access to food and helps them escape extreme conditions and insect harassment. The annual cycle involves a movement from their winter feeding grounds to their summer calving grounds. Winter ranges are often found in sheltered valleys or the boreal forests (taiga), where snow is less deep and food is still accessible. In spring, pregnant females lead the herds north to the open tundra, which serves as the traditional calving grounds. The exposed tundra in summer offers a brief period of fresh forage and provides a better chance to avoid predators, as well as a refuge from swarms of biting insects like mosquitoes and warble flies.
Sustenance in the Cold: Caribou Diet
The caribou’s diet changes significantly with the season, focusing on the specific plant life available in the northern environment. During the long, cold winter, their primary food source is lichen, often referred to as “reindeer moss”. This organism is crucial because, despite being low in protein, it is rich in digestible carbohydrates, providing the necessary energy for survival through the lean months. When the tundra’s short summer arrives, the caribou switch their diet to take advantage of the brief burst of growing vegetation. They graze on tundra grasses, sedges, and the leaves of dwarf shrubs like willow and birch. This summer diet is higher in protein and other nutrients, allowing the caribou to build up the fat reserves.