In northern Norway, on an island well within the Arctic Ocean, there is a very special population of voles.
These small rodents live on Spitsbergen, the main island of the Svalbard archipelago. They were introduced between 1920 and 1960, possibly from Russian mining-supply ships.
The species was first identified as the field vole (Microtus agrestis) found throughout Europe and Russia. However, genetic analysis and a recent taxonomic update have identified this species as the sibling vole (Microtus levis) which lives mainly in eastern Europe and western Russia.
Although they are not a species native to the Arctic, these voles have still found a suitable site to settle and thrive in a unique way.
In the region of Grumant, a former Russian mining settlement, there is a cliff where hundreds of Thick-billed Murres breed each year. The droppings produced by this colony of seabirds have progressively flowed down the cliff for hundreds of years or more, greatly enriching the soil below. Where the slope is softer, nutrient-rich soil allows the growth of a very rich flora. These grasses are an important source of food for voles when they come out of their burrows found in the nearby rocky outcrops.
Despite low predation because of their recent introduction, the vole population fluctuates irregularly and dramatically from about 200 voles per hectare to an almost total absence of voles.
Researchers from the University of Tromsø – The Arctic University of Norway and the Canadian Museum of Nature are working together to try to explain these fluctuations. Various hypotheses have been studied.
Early observations suggest that competition is so fierce during periods of high abundance that the resulting social effects (fighting, stress, changes in reproductive behaviour, etc.) reduce the survival and reproduction of voles. In addition, some voles do not reach maturity during periods of high density, which hinders the reproduction of the population. Finally, during two winters when ice crusts formed on the ground, the populations were almost decimated. This shows the importance of meteorological factors on the population dynamics of voles on Spitsbergen.
Spitsbergen is inhabited by nearly 3000 people. Its economic past included whaling, hunting fur animals and coal mining.
Although located in the High Arctic, the island is affected by the North Atlantic Drift, a marine current originating from the Gulf Stream. The average temperature of Spitsbergen varies between –14° C in winter and 6° C in summer. There is a rich fauna including a few thousand polar bears, a reindeer subspecies, thousands of Dovekies, Thick-billed Murres, and many other seabirds. Because of this rich biodiversity, two-thirds of the island is now protected and Spitsbergen is now a very popular tourist destination.
(Translated from French)