Mystery surrounds the discovery of oil-soaked birds found washed ashore on the Western Isles.

Around a dozen dead guillemots have been found so far, but wildlife volunteers fear the problem could be more extensive.

The birds are turning up on beaches and shorelines along a 100-mile stretch from South Uist to Lewis.

Most are washed up dead but one was found alive and is now being treated.

Coastguards say there are no reports of an oil spill at sea and a search along the Uist coastline has revealed no trace of pollution.

Sandy MacDonald British Divers Marine Life Rescue (BDMLR) Outer Hebrides branch, urged islanders to keep an eye out of oiled birds on the shoreline.

She said: "As yet we do not know what has caused this oil pollution or when or where it happened but affected birds have been found from the west coast of Lewis down to Eriskay.

"If found in time live birds can be successfully cleaned and treated before being returned to the wild.

"We would like people to keep an eye out. These birds could be absolutely anywhere. We don't know what cause this but it is covering a large area."

The first dead guillemot was found lying on a beach in Benbecula on New Year's Day.

Since then there have been regular reports of birds found on various shores, including Husinish, Harris and Sound of Harris.

Anyone who has spotted an oil-covered bird can call BDMLR on 01825 765546.