Peak years for lemmings are over: scientists think wetter winters in southern Norway are affecting them.
Norwegian and French scientists have found that numbers of the animals no longer vary over a regular cycle, as they did until a decade ago.
The BBC reports they think the snow is not stable enough to provide winter shelter for lemmings.
Writing in the journal Nature, they 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.
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.
Desperate searches led some to jump off high ground into water, leading to the popular - but wrong - assumption that they were prone to commit collective suicide.
Winters now too humid
However, the peak years are not occurring any more. The research team 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.
