Common and soprano pipistrelle are already resident in Scotland
Bat workers hope to confirm a rare species of bat is resident at a Scottish loch after its call was picked up on a bat detector.
Anne Youngman, of the Bat Conservation Trust, said there had been a "tantalising" encounter with a Nathusius pipistrelle at Loch Leven.
The species, which lives on continental Europe, is rarely recorded in Britain.
Meanwhile, Scottish bat workers are preparing to gather for their annual conference in Stirling on Halloween.
The meeting, which will feature a workshop on the effects of wind farms on bats, will be held at the University of Stirling on 31 October.
During the event, Dr Sue Swift, from Blairgowrie, will receive a national award.
She is the first woman to have won the trust's Pete Guest Award which recognises outstanding contributions to bat work. The previous five winners have all been men.
Ms Youngman said the Loch Leven Nathusius was heard making "social calls" marking it out as a male possibly searching for a mate.
Scotland is already home to the common and also soprano pipistrelle.
Chances of detecting the Nathusius again are growing increasingly slim as most bats have now begun hibernation.
The loch in Kinross, which was declared a nature reserve in 1964, attracts tens of thousands of geese each autumn.
A castle on an islet in the loch served as a prison for Mary Queen of Scots in 1567, before her escape.