In such cases, many drown if the body of water is an ocean or is so wide as to exceed their physical capabilities.
They can swim and may choose to cross a body of water in search of a new habitat. Driven by strong biological urges, some species of lemmings may migrate in large groups when population density becomes too great. It is not a deliberate mass suicide, in which animals voluntarily choose to die, but rather a result of their migratory behavior. Lemmings have become the subject of a widely popular misconception that they are driven to commit mass suicide when they migrate by jumping off cliffs. Worm published dissections of a lemming, which showed that they are anatomically similar to most other rodents such as voles and hamsters, and the work of Carl Linnaeus proved that they had a natural origin. This description was contradicted by natural historian Ole Worm, who accepted that lemmings could fall out of the sky, but claimed that they had been brought over by the wind rather than created by spontaneous generation. In the 1530s, geographer Zeigler of Strasbourg proposed the theory that the creatures fell out of the sky during stormy weather and then died suddenly when the grass grew in spring. Misconceptions about lemmings go back many centuries. įor many years, the population of lemmings was believed to change with the population cycle, but now some evidence suggests their predators' populations, particularly those of the stoat, may be more closely involved in changing the lemming population. Fluctuations in the lemming population affect the behaviour of predators, and may fuel irruptions of birds of prey such as snowy owls to areas further south. The lemming defence system is thought to be based on aposematism (warning display). Lemmings, by contrast, are conspicuously coloured and behave aggressively toward predators and even human observers. Lemming behaviour and appearance are markedly different from those of other rodents, which are inconspicuously coloured and try to conceal themselves from their predators. Why lemming populations fluctuate with such great variance roughly every four years, before numbers drop to near extinction, is not known. The Norway lemming and brown lemming are two of the few vertebrates which reproduce so quickly that their population fluctuations are chaotic, rather than following linear growth to a carrying capacity or regular oscillations. Like many other rodents, lemmings have periodic population booms and then disperse in all directions, seeking food and shelter their natural habitats cannot provide. In the spring, they move to higher ground, where they live on mountain heaths or in forests, continuously breeding before returning in autumn to the tundra. They make nests out of grasses, feathers, and muskox wool ( qiviut). Their burrows have rest areas, toilet areas, and nesting rooms. These rodents live in large tunnel systems beneath the snow in winter, which protect them from predators. They remain active, finding food by burrowing through the snow. Lemmings do not hibernate through the harsh northern winter. Like other rodents, their incisors grow continuously, allowing them to feed on much tougher forage. They digest grasses and sedges less effectively than related voles. Lemmings choose their preferred dietary vegetation disproportionately to its occurrence in their habitat. They also forage through the snow surface to find berries, leaves, shoots, roots, bulbs, and lichens. They are herbivorous, feeding mostly on mosses and grasses. They have a flattened claw on the first digit of their front feet, which helps them to dig in the snow. They have a very short tail, a stubby, hairy snout, short legs, and small ears. Lemmings are quite rounded in shape, with brown and black, long, soft fur.
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