For centuries, Norwegians have puzzled over why the population of hamster-like lemmings rises dramatically some years and crashes in others. So great is the fascination with these rodents of the far north that ancient Norwegian sagas, or legends, refer to them. In the popular imagination outside of Norway, lemmings are the strange animal the occasionally commits suicide in massive numbers by leaping off cliffs. This conception, it turns out, is a fantasy with no basis in fact, disseminated in largely by the 1958 Walt Disney "documentary," White Wilderness. (Reportedly, filmmakers paid Inuit hunters a bounty to collect lemmings then hurled the animals off the cliffs themselves.)

For decades scientists have also taken note of the strange behavior of lemmings. Researchers have shown that these animals, which only live in Arctic regions, go through cycles that are about four years long. Although figures vary depending upon region, the population of lemmings can easily multiply by a factor of two or three hundred over a period of just two years, before dropping down again. Scientists have learned how this is possible. Lemmings can have several litters in a year. Moreover, the virile animals become sexually mature only a month after birth.

However, these scientists still wonder why the numbers go up and down the way they do. There have many theories. One idea, which is now discredited even by its own author, is that lemmings die of stress when their numbers become too great. The cycle of sunspots has also been suggested as a possible explanation, though today scientists generally regard this idea as implausible. The two most likely explanations are that lemming cycles are controlled by the availability of food or by the activity of predators.

For the last 16 years, French biologist Benoit Sittler, who teaches at the University of Frieberg in Germany, has been studying Greenland's collared lemming on Traill Island in East Greenland. For about two months each summer, Sittler and a crew of graduate students and assistants scour about five square miles of prime lemming habitat for evidence of winter nesting. They also set traps alongside summer burrows to gauge the summer population.

Sittler and Olivier Gilg, who just completed a Ph.D. dissertation on lemmings at the University of Franche-Comté in France, have concluded that, at least on Traill Island, it is the interaction between the lemmings and their primary predator, the ermine, that controls the population of the small rodents. The two researchers have shown that the peaks and valleys of the ermine population always follow those of the lemming population by a year.

This year there were virtually no lemmings on Traill Island, an unexpected finding since it has been four years since the lemming population last peaked, and since the time between peaks and valleys is usually only two years. Arctic foxes, which eat lemmings during the summer, have had to find other food because the lemmings were absent. So the numbers of Arctic hare, eider ducks and geese--all alternate food for the foxes--were also low. Snowy owls, which frequent Traill Island when lemming numbers are high, were absent.

	Lemmings See photos of the scatological remains lemmings in Greenland.