The Arctic tundra is a vast, desolate expanse, where extreme cold, limited light, and a short growing season present challenges to life. Temperatures can plummet to -40 degrees Celsius or colder, and much of the ground remains permanently frozen as permafrost. Despite these harsh conditions, a surprising array of herbivores manage to survive and thrive. Their existence in this unforgiving environment raises questions about how they endure the cold and find sustenance.
Prominent Arctic Herbivores
The Arctic tundra is home to several distinct herbivore species. Muskoxen, large hoofed mammals weighing between 500 to 800 pounds for males, form herds of 12 to 24 individuals in winter, huddling for warmth and defense. When threatened, adults form a protective ring around their calves, facing outward with their formidable horns. Caribou, known as reindeer in Eurasia, are highly social, forming vast herds that can number in the hundreds or thousands, undertaking extensive migrations across the landscape. Both male and female caribou grow antlers, which are shed annually.
Smaller inhabitants of the tundra include the Arctic hare, a robust lagomorph typically weighing 6 to 12 pounds, often found alone but sometimes gathering in groups for warmth during winter. Lemmings are stout, small rodents, around six inches long, with dense fur, known for their dramatic population fluctuations. They are solitary except during mating season. The Rock Ptarmigan, a medium-sized game bird weighing about 450 to 640 grams, is the only terrestrial bird that remains in the high Arctic year-round, often congregating in flocks outside of breeding season.
Tundra Diets and Foraging Strategies
Arctic herbivores navigate a landscape with a short growing season, relying on specialized diets and foraging techniques. Common tundra vegetation includes lichens, mosses, sedges, grasses, and dwarf woody plants like willow and birch. Caribou, for instance, primarily consume lichens in winter, which they locate using their keen sense of smell, even under deep snow. They employ a technique called “cratering,” using their large, shovel-like hooves to dig through snow to reach the buried forage.
Muskoxen use their strong sense of smell to find food beneath the snow, digging with their front hooves or breaking through snow crusts. Their diet is sparse in winter, consisting of dried grasses, sedges, willows, and lichens, but expands to include willow leaves, tussocks, grass shoots, and flowers in spring. Lemmings, active year-round, tunnel under the snowpack to access sedges, grasses, and mosses, often in the soft “depth hoar” layer at the base of the snow. This subnivean environment provides access to food and shelter.
Survival Adaptations for a Frozen World
The physical and behavioral traits of Arctic herbivores are adapted to withstand extreme cold. Muskoxen possess a two-layered coat: long outer guard hairs and a thick, woolly underfur called qiviut, which is eight times warmer than sheep’s wool and finer than cashmere. Their compact, barrel-shaped bodies and short legs minimize surface area, reducing heat loss. Caribou also have a dual-layer coat with hollow guard hairs that trap air, providing excellent insulation and buoyancy for swimming.
Caribou hooves are proportionally larger and crescent-shaped, with flexible pads that harden and allow hair to grow between the toes in winter, providing traction on ice and snow. Arctic hares have shortened ears and limbs, a small nose, and a thick coat, with fat comprising nearly 20% of their body mass. They also change their fur color seasonally, from brown or gray in summer to white in winter, for camouflage against the snow. Similarly, Rock Ptarmigans undergo molts annually, changing from mottled brown in summer to pure white in winter to blend with their snowy surroundings. Their feathered feet act like snowshoes, aiding movement and providing warmth.
Ecological Importance of Tundra Herbivores
Tundra herbivores play a role in shaping their ecosystem. Their grazing activities influence plant communities, helping to maintain species balance by consuming common vegetation like shrubs, which can otherwise shade out lower-lying plants. This grazing promotes plant diversity and affects nutrient cycling in the soil, as their waste products contribute to nutrient concentrations.
Beyond their direct impact on vegetation, these herbivores form the base of the terrestrial food web for many Arctic carnivores. Lemmings, in particular, are a primary food source, and their dramatic population cycles directly affect the breeding success and populations of predators such as Arctic foxes, snowy owls, and various hawks and weasels. Fluctuations in lemming numbers can lead to changes in predator populations, highlighting their interconnectedness in this Arctic environment.