The lemming's legendary leaps off high cliffs and massive migrations into the sea may not be intentionally suicidal, but the outcome is frequently the same. This well-known migratory behavior is typical of Scandinavian lemmings in Norway, Sweden, and Finland who move rapidly across the countryside in large groups when food supplies are scarce. Obsessed with finding food, they sometimes jump (or actually fall off) cliffs or jump into oceans and rivers, not as an act of suicide but merely to cross the watery barrier in their search for food. Lemmings are actually good swimmers, though they may not have the best judgment about their stamina.
North American lemmings engage in the same kind of food searches except they are solitary and shun large herds. In both cases, the strange and self-destructive behavior is a result of the lemmings' unfortunate lack of built-in population control mechanisms that most species have. Instead of cutting back on breeding in times of famine, the energetic little rodents continue to mass produce themselves until the environment can no longer support them; then they move out en masse looking for new food sources or die in the process. The populations tend to peak every four years or so and then crash almost to extinction.
The smallest of the High Arctic mammals, the mouselike rodents, despite their seemingly unstable lifestyle, are a key species in arctic ecosystems. They support many other species and at the same time help control predator populations, such as the arctic fox, ermines, Snowy owls, and falcons, with their boom-crash life rhythms.
Adult brown lemmings are about 150 mm from tail to snout and weigh about 55-115 g. Their coats change colors with the seasons, from brown to gray or from a multi-colored "collared" design to solid white in summer and winter, respectively. Despite the frigid environment, lemmings don't hibernate through the long arctic winter, but their round bodies, very short ears, legs and tails and thick winter coats help them conserve body heat. The frozen tundra is too hard to dig burrows in, but the lemmings create large nests of finely shredded grasses on the ground surface, and snow provides further insulation. In fact, lemmings spend most of their time foraging in the space between the snow and ground surface where the temperatures reach a toasty -25C. Not surprisingly, few lemmings live to see a second winter.
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