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  Main page: Nature & the Environment: Nature in Finland   

Nature in Finland

Written for Virtual Finland by Eeva Liisa Hallanaro,
M.Sc., Environmental Expert

Legendary lemmings

The Norway lemming’s range is limited to the arctic fells and tundra of northern Fennoscandia – where it is found in north-westernmost Russia and northern parts of Finland and Sweden, as well as in Norway.

Photo: Nature Photo Agency/Heikki
The numbers of Norway lemming in northernmost Finland vary greatly from year to year, but during good lemming years these small animals seem to pop up everywhere, especially on migration between their winter and summer feeding grounds.

But this very limited global distribution is not the Norway lemming’s only peculiarity, since this small rodent is also notorious for the extreme fluctuations in its numbers. Some years they seem to be everywhere, but during other years they are only conspicuous by their absence.

Lemming populations, like those of other northern rodents, typically exhibit pronounced cyclical variations over periods of 3 –5 years, with numbers in peak years dozens of times higher than during population slumps. The heights of these peaks also vary, with Norway lemming populations evidently having particularly high peaks every 30 years or so.

During these special lemming years, populations are so dense that hikers on the fells of northern Lapland can hardly move without sending the creatures scurrying off in every direction. Some lemmings also become so fearless that they will boldly stand their ground.

Lemming years have fired people’s imagination since the middle ages. Some believed that lemmings fell from the sky like rain, while others even suggested that the animals were searching for their former home, the lost continent of Atlantis. Priests even registered mass occurrences of lemmings in church diaries, as they were also thought to be an omen of war.

Photo: Reijo Juurinen
Click to enlarge the picture
Stoats and weasels commonly prey on Norway lemmings and other rodents in northern Finland. This stoat is in its summercoat.

A still more persistent piece of folk wisdom claimed that hordes of lemmings would suicidally rush off cliffs, fall into the sea and drown. Many people may even remember witnessing this phenomenon in an old American TV "nature documentary"; but this was in fact an elaborately staged stunt, involving captive lemmings released en masse, and deliberately driven towards some photogenic cliffs.

Two more scientific explanations have more recently been put forward to explain the phenomenon of lemming years.

The first and more widely accepted theory concerns the predators that feed on lemmings – particularly weasels and stoats. Lemming populations can increase during periods when there are relatively few predators; but predator populations will then increase, and consume more lemmings, soon causing a downturn in their numbers. With their prey in short supply, the predators will subsequently themselves decline, until the whole cycle can begin again.

The other theory holds that during lemming population peaks mosses can produce and accumulate toxic or foul-tasting chemicals to protect themselves from the voraciously grazing rodents. This will reduce the available food supply, and consequently lemming numbers, until the mosses no longer need to produce the deterrent chemicals. The lemmings can then start to feed on the mosses again, and proliferate.

Published November 2002



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Legendary lemmings

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