OSLO Lemming numbers are dwindling in Norway because of climate change, ending a historic cycle of population booms and busts that inspired a myth of mass suicides by the rodents, scientists said on Wednesday.
Fewer lemmings -- small brown, black or yellowish mammals -- in the mountains of south Norway meant predators such as the Arctic fox were forced to eat other prey including grouse and ptarmigan birds.
"The lemming population is falling and the peaks are disappearing," said Nils Stenseth of Oslo University, one of the authors of the report published in the journal Nature and written with colleagues in Norway and France.
He told Reuters it was the first study to link lemming numbers and disruptions to snowfall caused by global warming. The study of lemmings since 1970 showed the last population boom was in 1994, ending a pattern of spikes every 3-5 years.
Female lemmings can have litters of up to 12 young three times a year and the population can rocket if they are able to live sheltered from predators in early spring in gaps between powdery snow and the ground where they eat moss and other plants.
But warmer temperatures in recent years meant snow was wetter, often turning hard and icy. That made it more difficult for rodents to hide and reach food.
"A relatively small effect on one particular species is having a broad effect on the system," Stenseth said. In years with a lemming population boom, predators such as Arctic foxes or snowy owls used to get a valuable boost.
"Now when the lemming peak is gone...they will prey on other species such as ptarmigan and grouse," he said.
Tim Coulson of Imperial College, London, wrote in Nature in a commentary on the study that lemmings were so common in north Norway in 1970 that "snowploughs were used to clear the vast numbers of squashed animals from roads."
But population surges quickly led to food shortages and mass migrations. "On occasion, desperate to find food, they jump into water and start swimming. This behavior led to the myth that lemmings commit suicide," he wrote.
Lemmings are, however, still abundant. "We are a long way from it being a threatened species," Stenseth said. Temperatures in late winter and early spring in southeastern Norway in recent decades were the highest since records began in 1756.
The U.N. Climate Panel projects that temperatures will keep rising, bringing more droughts, floods and heatwaves. Man-made emissions of greenhouse gases, mainly from burning fossil fuels, are the main cause, it says.