For centuries the timid wood mice of Canna lived in isolation among the ragged landscape of the Inner Hebrides, evolving their own genetic line and growing more than 25 per cent larger than their mainland relations.
However, the accidental introduction 100 years ago of brown rats to the island, which lies 26 miles off the west coast of Scotland, has not only threatened many species of seabirds, but also inadvertently put the unique mice breed in danger.
A £500,000 project to wipe out the rats and protect the seabirds would have destroyed the mouse population, but conservationists have mounted a rescue mission to ensure the rare creatures will not end up as innocent victims of Canna's rodent wars.
Hundreds of the genetically unique mice were rounded up and taken to the mainland before experts begin to lay more than 23 tons of poison to kill the rats.
Now, enough of the wood mice have been removed from Canna to be split into two breeding populations, one at Edinburgh Zoo and the other at Highland Wildlife Park in Kingussie, near Inverness.
A breeding programme will be carried out and the mice returned once every rat has been eradicated from Canna.
"Leaving the mice would have been a serious risk in terms of biodiversity," said Jeremy Usher-Smith, manager at the wildlife park.
"They are extremely rare and valuable and once the last one of the species is lost then this strain of mouse would be extinct. They are unique to the island.
"By doing this we are making sure the population now has the chance to become established once the rats have gone."
The rats first arrived on Canna on ships and fed on seabirds' eggs. The island's spectacular 600ft-high basalt cliffs were once a sanctuary for various species of seabirds, but in the past 10 years a combination of climate change and an explosion in the rat population has devastated the colonies of shags, fulmar, kittiwakes, razorbills, puffins and guillemots. The Manx shearwater is now extinct as a breeding bird on the island.
The cull is being carried out by New Zealand specialists, Wildlife International, as part of Operation Canna Recovery, a continuing project launched by the island's owner, the National Trust for Scotland.
Starting next January, more than 4,000 bait traps are to be laid across Canna, which is just four-and-a-half miles long by a mile wide, with members of the specialist team abseiling down cliffs and climbing rock faces to reach the rat nests.
"The rats have to be poisoned as seabirds are in serious decline and the primary cause of this is rats on the island," said Richard Luxmoore, head of nature conservation at the National Trust for Scotland.
The 12-strong team of specialist exterminators, who outnumber the resident crofting population of Canna, will leave the 2ft-long white plastic tube traps, some of them smeared with peanut butter to tempt their prey, on the island over the winter months.Reuse content