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Massive population bursts in small arctic rodents called lemmings were so legendary that they became folklore. In days gone by, thousands migrated across the Scandinavian tundra every three to four years. But since 1994 there has been no boom-and-bust cycle. On page 93, Nils Christian Stenseth, a theoretical ecologist at the University of Oslo, and his colleagues piece together disparate long-term data sets to substantiate growing speculation that climate change is affecting lemming population dynamics. Stenseth tells Nature that lemming population cycles could disappear altogether.

In a boom, do lemmings really jump off cliffs?

The biggest misconception about lemmings — widely circulated by a 1950s Disney movie — is that they purposefully march to the sea to commit suicide. In reality, during peak years, lemmings are driven to move downhill to explore new habitat. Some can accidentally head into the sea, but it is a random process amplified by the sheer number of lemmings.

What types of data did you compare with lemming density counts?

We used snow-condition data collected by university students taking winter ecology courses at the Finse Alpine Research Center. First author Kyrre Kausrud built a time series from the student reports and modelled meteorological data from nearby field stations to fill in gaps in the data. We also incorporated hunter-reported bird catches to show that certain bird populations exhibit similar fluctuations because they are secondary prey for predators whose abundance increases during rodent population bursts.

How does climate change affect lemmings?

Our data show that fluctuations in temperature and humidity cause the lowest layer of the snowpack, where lemmings live and reproduce during winter, to harden drastically — making it difficult for lemmings to reproduce. If lemming cycles disappear, the region's entire community structure may be altered.

What have you learned from this work?

That it is crucial to collect, maintain and make available long-term data sets of biodiversity — which I hope becomes a higher priority.

Will lemming folklore be replaced by a climate-change fable?

Perhaps. Lemmings are a charismatic species, but their distinctive population cycles were part of a past when climate was different. To see climate change so clearly affecting nature might make people realize how important ecological changes can be.