Page last updated at 19:14 GMT, Wednesday, 5 November 2008

Climate pushing lemmings to cliff

In warm years, lemmings are the most plentiful mammals

Climate change is bringing wetter winters to southern Norway, a bleak prospect for the region's lemmings.

Scientists found that numbers of the animals no longer vary over a regular cycle, as they did until a decade ago; there are no more bumper years.

The snow is not stable enough, they think, to provide winter shelter.

Writing in the journal Nature, the researchers suggest the lack of Norwegian lemmings is affecting other animals such as foxes and owls.

In boom years, lemmings are the most plentiful and important prey for these carnivores.

Until the mid-1990s, the lemming population in the study area in southern Norway varied on a cycle of three to five years.

Lemming skeleton
The animals can live for three to four years making use of snow cover

Rather than hibernating, lemmings spend the winter living in the space between the ground and a stable layer of snow above.

Dry winters would allow large numbers to survive until spring, resulting in a population explosion.

On occasions, there were so many that snowploughs were deployed to clear squashed animals from roads.

These years often saw Norwegian lemmings (Lemmus lemmus) having to compete hard for food.

The desperate search led some to jump off high ground into water, leading to the popular - but wrong - assumption that they were prone to commit collective suicide.

But the peak years are not occurring anymore. The research team, composed of Norwegian and French scientists, believes the winters are now too humid, leading to the "wrong kind of snow".

This results in a less stable subnivean space (the space between the ground and the snow layer above), meaning substantially fewer animals survive until spring.

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