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The "mysterious" Orkney vole is likely to have originated from Belgium 5,100 years ago, researchers have said.

The team of scientists - led by the University of Aberdeen and Cornell University in America - believe the subspecies of the European common vole was brought over by farmers.

They say it is found nowhere else on the UK mainland or islands.

The Belgium findings are described by the research team as a "totally unexpected result".

'Mystery for decades'

Prof Keith Dobney, one of the co-directors of the research, said: "The extensive archaeological record from Orkney has produced thousands of their [voles] bones and teeth, suggesting that they most likely arrived with early farmers or through Neolithic maritime trade and exchange networks.

"Where in Europe they came from and exactly when they were introduced has been a mystery for decades, but new genetic techniques and direct dating of their bones have finally allowed us to answer these questions."

Dr Natalia Martinkova who carried out the genetic studies on living common voles from continental Europe and Orkney, said: "Although our modern DNA results did not reveal exact genetic matches with any populations we sampled across continental Europe, the closest were from populations living today on the coast of Belgium, the likely origin for the original Orkney populations."

The findings are published .