By Steven McKenzie
Highlands and Islands reporter, BBC Scotland news website
The bat was photographed by Steve Duffield
A birdwatcher is believed to have made the first recorded sighting of a species of bat not previously seen on the Western Isles.
The Bat Conservation Trust hopes to confirm it was a noctule from images captured by Steve Duffield.
Pipistrelle, a smaller animal, is among the few species found on the isles.
Anne Youngman, the trust's Scottish officer, said it was highly likely it was a noctule but could be the rarer Leisler's bat.
There was an earlier theory that the bat was blown hundreds of miles off course while making a migration in North America, but experts now believe it may have arrived from mainland Scotland.
Mrs Youngman said the trust's experts also believed the bat could be a Leisler's, a species previously recorded in Dumfries and Galloway, if not a noctule.
Mr Duffield photographed the bat flying in daytime on South Uist on Wednesday when the weather was warm.
Pipistrelle, a smaller animal, is among the few species known to live on the isles.
Mrs Youngman said it could be the first recorded sighting of a noctule on the Outer Hebrides and the most northerly and westerly record of one in the UK.
Meanwhile, the bat officer has also received a report from Skye of a peregrine falcon chasing two bats in daytime.