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.

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.