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Orkney Vole Microtus arvalis orcadnesis Length 12-17cm Confined to Orkney. Introduced, but has been present on those islands for at least 5,000 years and lives on moors and coastal cliffs. Also occurs on mainland Europe where it is known as Common Vole. Although absent from, and not native to, most of Britain, it occurs as an ancient introduction to two far-flung island chains; here it has evolved into distinct subspecies.