For centuries, people have puzzled over lemmings, the northern rodents whose populations surge and crash so quickly and so regularly that they inspired an enduring myth: that lemmings commit mass suicide when their numbers grow too large, eagerly pitching themselves off cliffs to their deaths in a foamy sea.
Scientists debunked that notion decades ago. But they have never been certain what causes the rapid boom-and-bust cycles that gave rise to it. Now, in a study of collared lemmings in Greenland, published on Friday in the journal Science, a team of European researchers reported that the real reason has nothing to do with self-annihilation and everything to do with hungry predators.
After 15 years of research, the scientists report, they discovered that the combined actions of four predator species -- snowy owls, seabirds called long-tailed skuas, arctic foxes and weasel-like creatures known as stoats -- create the four-year cycles during which lemming populations explode and then nearly disappear.
Scientists say such cycles have been one of the most enduring -- and hotly debated -- mysteries in ecology.
"There have been several dozen hypotheses and sometimes everybody was almost killing each other they were sticking so close to their hypothesis," said Olivier Gilg, an ecologist at the University of Helsinki in Finland who is an author of the paper.
Many suspected the cycles might be caused by an array of forces, Gilg said, "but we were able to explain this cycle with only predation, and that was very surprising; it was very exciting."
Peter Hudson, a population ecologist at Penn State University who was not involved with the work but who wrote a commentary for Science on the paper, called it a textbook case, noting that population cycles are also found in birds, insects and larger mammals, like lynx.
"These animals show this lovely clockwork change in numbers," he said of lemmings, "and yet we haven't been able to nail it down. This paper reveals the mechanism. That's why this study is particularly important."
Though their research deals with brown 18cm rodents, ecologists can be forgiven their excitement. Lemming population cycles have captured human imagination for hundreds of years. In Scandinavia, ancient sagas describe lemming outbreaks, and as early as the 1500s there were writings attempting to explain why lemmings would periodically overrun regions, some suggesting that the animals rained down from the sky.
Recently, scientists have tested more plausible explanations, including climate change and the idea that the quality of plants eaten by lemmings might vary cyclically or that high densities might stress lemmings, decreasing their ability to reproduce and causing populations to crash. Even sunspots had been proposed as a possible cause.
In the new study, researchers took advantage of Greenland's never-ending daylight in summer to do extended observations of predators. The open tundra environment also allowed the small, skittering rodents to be seen and counted easily.
The scientists found that the tundra provided an excess of food and of sandy soil to burrow in, a setting for explosive lemming population growth.
But when lemming numbers began to soar, foxes, skuas and owls began eating them in greater and greater quantity. A pair of snowy owls can bring back as many as 50 lemmings a day for their hungry nestlings.
Stoats specialize in hunting lemmings, and after a banner lemming year, stoat populations explode, decimating the lemmings the following year. Then the four-year cycle begins all over again.
When researchers created a model to predict lemming populations, based only on the behavior of their four predators, they found that the model precisely predicted nature's four-year fluctuations in numbers.
Despite the new finding, lemming scientists expect to continue to be plagued by suicide queries. In particular, they blame a 1958 Walt Disney nature film, White Wilderness, in which lemmings were shown hurling themselves off a cliff.
In 1983 a Canadian documentary, Cruel Camera, about abuse of animals in movies, asserted that the scene was faked, using lemmings bought from Eskimo children and herded into the water. That conclusion has come to be widely accepted, and on Thursday Rena Langley, a spokeswoman for the Walt Disney Co, did not dispute it.
"We have done extensive research into what happened more than 40 years ago," she said, "but have been unable to determine exactly what techniques were used in producing White Wilderness. The standards and techniques were certainly different then than they are now."
With the midday sun blazing, an experimental orange and white F-16 fighter jet launched with a familiar roar that is a hallmark of US airpower, but the aerial combat that followed was unlike any other: This F-16 was controlled by artificial intelligence (AI), not a human pilot, and riding in the front seat was US Secretary of the Air Force Frank Kendall. AI marks one of the biggest advances in military aviation since the introduction of stealth in the early 1990s, and the US Air Force has aggressively leaned in. Even though the technology is not fully developed, the service is planning
INTERNATIONAL PROBE: Australian and US authorities were helping coordinate the investigation of the case, which follows the 2015 murder of Australian surfers in Mexico Three bodies were found in Mexico’s Baja California state, the FBI said on Friday, days after two Australians and an American went missing during a surfing trip in an area hit by cartel violence. Authorities used a pulley system to hoist what appeared to be lifeless bodies covered in mud from a shaft on a cliff high above the Pacific. “We confirm there were three individuals found deceased in Santo Tomas, Baja California,” a statement from the FBI’s office in San Diego, California, said without providing the identities of the victims. Australian brothers Jake and Callum Robinson and their American friend Jack Carter
Le Tuan Binh keeps his Moroccan soldier father’s tombstone at his village home north of Hanoi, a treasured reminder of a man whose community in Vietnam has been largely forgotten. Mzid Ben Ali, or “Mohammed” as Binh calls him, was one of tens of thousands of North Africans who served in the French army as it battled to maintain its colonial rule of Indochina. He fought for France against the Viet Minh independence movement in the 1950s, before leaving the military — as either a defector or a captive — and making a life for himself in Vietnam. “It’s very emotional for me,”
UNDER INVESTIGATION: Members of the local Muslim community had raised concerns with the police about the boy, who officials said might have been radicalized online A 16-year-old boy armed with a knife was shot dead by police after he stabbed a man in the Australian west coast city of Perth, officials said yesterday. The incident occurred in the parking lot of a hardware store in suburban Willetton on Saturday night. The teen attacked the man and then rushed at police officers before he was shot, Western Australian Premier Roger Cook told reporters. “There are indications he had been radicalized online,” Cook told a news conference, adding that it appeared he acted alone. A man in his 30s was found at the scene with a stab wound to his back.