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Bank Voles from Germany

The Irish Bank Vole is not a native Irish mammal, but rather an alien or introduced species. The first Irish sighting was in 1964, when the then-student

Dr. Andre Claassens, came across it near Listowel in Co. Kerry. It is found over a wide geographical spread in the northern hemisphere, running from Western Europe (Spain) to Siberia. Bank Voles (Clethrionomys glareolus) are also common in Scotland, England and Wales, although rarer in islands off Great Britain. Since its introduction to Ireland it has spread through the south west.

It is quite a mystery as to why there were no voles in Ireland until recently. The Field Vole associates itself more with humans than the Bank Vole, so one would expect the Field Vole to have arrived here first at some point since the last Ice Age. The fact that the Bank Vole arrived before the Field Vole added to the mystery. Scientists also expect new alien mammalian species to arrive on the East coast of Ireland, it being closer to Great Britain and mainland Europe; the Bank Vole appears to have arrived on the West coast first! So how did shy little Bank Voles get here, and where did they come from?

The current hypothesis suggests that the Bank Vole was introduced to Ireland in the 1920s during work on the Shannon hydroelectric scheme. Large machinery for this development was shipped from ports in the north of Germany to Foynes on the river Shannon and some other Irish ports. The machinery was then transported to Ardnacrusha for use in the hydroelectric scheme. The Bank Vole appears to have landed at Foynes and then after some time adapting to its new home there, spread throughout county Limerick and parts of north Kerry.

In a recent paper in the Irish Naturalists Journal (Vol. 28, No. 11, 2007) this hypothesis has been examined using DNA analysis. The team of scientists from Ireland, the UK, the USA and the Czech Republic compared the DNA of 34 Irish Bank Voles with those found in Scotland, and Germany (30 specimens). The results showed that there was very little genetic (DNA) variation among the 34 Irish voles. This supports the hypothesis that they arrived here recently and in a single small group (they all knew each other very well). The DNA also showed that they are more closely related to the 30 German specimens than to the 10 Scottish ones. However, analysis could not pinpoint the location of the population of Bank Voles in Germany that may have given rise to the Irish population.

Of the 30 German specimens, 21 were taken from the Heidenheim region and 9 from the Ravensgerg region.
These were the locations where the hydroelectric machinery was constructed in the 1920s. However, the scientists were unable to examine the DNA of voles found around the north German ports from where the machinery was shipped to Ireland. The ports could just as easily have supplied the population of stowaway voles. It would seem imperative to follow up this in a further study. The vehicles used to transport the hydroelectric machinery from Heidenheim and Ravensberg were likely called in from other parts of Germany. These vehicles may also have been carrying stowaway voles. This possibility also needs further examination.

See Bank Vole portrait

Text © Paul Whelan, 2008
Photos © Eddie Dunne & John Murphy.