Conservationists have carried out a survey of seabirds on the outlying islands of a remote archipelago for the first time in 20 years.
St Kilda, home to nearly one million seabirds, lies 40 miles out into the Atlantic Ocean to the west of the Outer Hebrides.
Its last residents were evacuated in 1930.
The bird population has not been surveyed for two decades because it is so difficult to land on some of the islands.
But a team led by National Trust for Scotland (NTS) senior nature conservation adviser Richard Luxmoore succeeded in carrying out surveys on three of them last month.
Mr Luxmoore said: “When we saw the island, it was clear why it was 20 years since the bird population had been last surveyed.
“At first sight, Boreray looks completely inaccessible, rising through an impenetrable jumble of pinnacles and cliffs to 380 metres.
“It is accurately described as awesome. We had passed it on the way to Hirta and what we saw of the landing site was not encouraging.
“Even on a calm day, the Atlantic swell can run several metres up the sloping slab of rock whose size is belied by the scale of the island.
“On the advice of the boatman, Angus Campbell, we chose to land in the evening – at high tide – as the band of seaweed-covered rock that we would have to cross would be narrowest.”
The eight-strong group spent five days on Boreray, surveying the population of birds such as puffins, Leach’s storm-petrels and Manx Shearwater.
They had to land on the island to carry out the survey as while cliff-nesting seabirds such as gannets, fulmars and guillemots can be counted from a boat, the burrow-nesting seabirds must be counted on the ground.
Puffins are relatively simple to count as their burrows are easy to detect due to debris left around the entrance but shearwaters and storm petrels are much more difficult and can only be located by playing recordings of their calls and listening for their response.
After five days on Boreray and a night back on the main island of Hirta, the researchers landed on Soay to count the birds there.
Mr Luxmoore said: “It rained overnight, which made the landing place even more slippery and treacherous and necessitated the utmost caution.
“We took four hours to get off but achieved it safely and without incident.”
They also surveyed the bird population on the island of Dun.
Mr Luxmoore said analysing the results of the survey is “a complex task” and it will be some time before the results are known.
St Kilda is the UK’s only dual Unesco World Heritage Site – for natural and cultural heritage – and is home to the UK’s largest colony of Atlantic puffins.
There was a community there for 4,000 years before it was evacuated on August 29 1930 after the remaining 36 islanders voted to leave as their way of life was no longer sustainable.
The uninhabited archipelago has been in the care of the National Trust for Scotland (NTS) since 1957.