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Lemming population explosions may be powered by their ability to breed through the long, dark Arctic winters. The finding adds to evidence that lemmings will be hit hard by climate change.

and colleagues at the University of Tromsø trapped and at 109 locations in north-east Norway to monitor population changes before, during and after a lemming population outbreak.

As the winter went on, the population of lemmings living under the snow at each site rose, while vole populations fell. In the spring, the lemming population was large enough to fuel an outbreak. Although the vole population also saw a large rise, it happened at a much slower rate.

Snow business

This suggests the lemmings’ huge outbreaks are largely driven by their winter behaviour, rather than external factors like food supply or predators, which should have had a similar impact on vole populations. Ims thinks this evolved to help the animals escape summer predators.

Lemmings bred fastest at high altitudes thanks to longer-lasting snow – but rising temperatures could see these snow-covered areas shrink, fragmenting lemming populations, says Ims.

Ideal winters for lemmings are becoming less common, says agrees of the University of Helsinki in Finland. But of the University of British Columbia in Vancouver, Canada, is not yet convinced that climate change will harm lemmings. He says that what is needed now is a detailed study of lemming populations living under the snow – but concedes that this is “difficult and expensive” with current existing technology.

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