Global warming and resultant climate change seem to be the culprit for shrinking lemming populations in Norway, says a new study.
Lemming populations throughout Scandinavia tend to explode naturally every three to five years, causing huge numbers to go in search of food.
Occasionally, this leads the rodents to jump into water and swim to new pastures, which is how the myth of lemmings committing mass suicide originated.
When lemmings boom, they're hard to miss. Norwegians have had to use snowplows to clear the squashed rodents off the roads.
But, in recent years, outbreaks have become a rarity in many parts of Scandinavia.
According to a report in National Geographic News, Kyrre Kausrud, a professor at the University of Oslo in Norway, and his colleagues analyzed lemming boom-bust cycles since 1970 for one site in southern Norway, which revealed that lemmings in this region have not had a population explosion since 1994.
Climate data collected over the same period suggest that warmer temperatures can explain why the rodents' numbers have remained low for more than a decade.
During the winter lemmings live in tunnels under the snow. Warmth from the Earth melts some of the snow near the ground, providing pockets of air and access to food such as moss.
In recent years, warmer temperatures have been changing the structure of the snow-with devastating effects for the lemmings.
Rather than remaining below freezing for most of the winter, temperatures have bounced above freezing a number of times, melting and then refreezing the snowpack.
"This enables water to enter the system, flooding the snow tunnels and then forming ice layers on the ground," Kausrud said.
Many lemmings drown when their burrows are flooded, and those that survive often starve when their food is trapped under an icy layer.
The team's data showed that lemming population explosions were linked to years with colder winters, providing the ideal snow conditions for lemmings to thrive.
They also showed that winters in southern Norway have been warmer since 1994, preventing females from rearing the large broods that lead to lemming outbreaks.
"Their findings present a convincing demonstration of the effects of climate change on lemmings and their wider ecosystem," said Tim Coulson, a population biologist from Imperial College London.
Kausrud and his colleagues think that it is unlikely that climate change will drive lemmings to extinction, but the impact on the ecosystem could be severe.
"As competitive relationships change for predators, prey, and plants, the whole community changes," he said.