The calls of a small seabird have been recorded for the first time on a group of islands in The Minch.
Conservationists hope the sound of storm petrels’ “churring” is an indication that an effort to eradicate rats on the Shiant Islands is working.
The black rats are not native to the islands off Lewis and are thought to be the descendants of rats that came ashore from shipwrecks in the 1900s.
Storm petrels are not found where there are rats, which eat their eggs.
On the Shiants, colonies of puffins, razorbills and guillemots have been in decline, while Manx shearwaters and until now storm petrels have not been found at all.
RSPB Scotland, Scottish Natural Heritage and the Nicolson family, which owns the islands, secured funding to start the rat eradication work in 2015.
They hope it will be possible to declare the islands rat-free next March.
Storm petrels, which are slightly bigger than a sparrow, had been seen flying past the Shiants.
To encourage them to breed on the islands, conservationists played the sound of their calls from a loud speaker.
This summer, real storm petrels’ churring was heard and the birds seen at a burrow by conservationists using night vision equipment.
Dr Charlie Main, senior project manager for the Shiant Isles Recovery Project, said: “The churring of a storm petrel is very distinctive and we’re delighted that it’s been recorded on the Shiants this summer.
“While we are still some way off the islands being officially declared rat-free, these calls indicate that all the biosecurity work we’re doing to keep these islands predator-free and make them ideal breeding sites for seabirds is paying off.”
She added: “The long-term aim is to allow a breeding colony of storm petrels to establish at the Shiants.”
Dr Andrew Douse, policy and advice manager in ornithology at Scottish Natural Heritage, said the first recording of the birds was “very welcome”.
He said: “Storm petrels only occur on islands without rats, which means that they are very vulnerable to the effects that arise from invasive species such as these.
“The Shiants are an ideal breeding location for storm petrels and hopefully they will go on to become an important stronghold for this species.”