A shortage of food has pushed the seabird colonies in the Northern Isles into an unprecedented crisis.
The Royal Society for the Protection of Birds has revealed that this year has been the worst on record for the birds in Orkney and Shetland, which have produced fewer young than in any previous year.
Almost all seabirds breeding in Shetlands internationally important colonies feed on sandeels, which have become increasingly scarce.
The society says guillemot colonies have been devastated for the second year running. The birds can fly many miles to find shoals of sandeels and can dive to more than 100 metres below the surface to catch them. However, the vital food is becoming difficult to find.
Other species, such as Arctic terns and kittiwakes, have also been severely affected, with poor breeding numbers and survival rates. This year no tern or kittiwake chicks were reared in the south of Shetland.
Great skuas, known as bonxies in Shetland, have also suffered a severe breeding failure. A lack of food has led the sometimes predatory species to feed on other seabirds and even the young of other skuas. At most skua colonies this year no young are expected to fledge.
Pete Ellis, the RSPBs Shetland area manager, said: "The situation is still getting worse for our struggling seabirds. The failure of almost all great skuas to rear young is unprecedented, and the populations of some species such as Arctic skuas are now reaching critical levels and the future for them looks bleak here."
Martin Heubeck of Aberdeen University, who has recorded seabird breeding success at Sumburgh Head for almost 30 years, said: "This has been an almost unbelievably bad breeding season. The scale of the breeding failure of guillemots is unprecedented in Europe."
The shortages of sandeels could be down to climate change affecting sea temperatures and currents, which may have reduced plankton on which the sandeels feed, forcing the small fish to move out of reach for many seabirds.
RSPB Scotland has called for urgent research into the problems and for improved marine-protection legislation.
The sandeel fishery in Shetland is now managed by an agreement between the Shetland Fishermen's Association, RSPB Scotland and Scottish Natural Heritage, with the aim of helping the birds.
The number of Arctic skua in Shetland has fallen by 42 per cent since a seabird survey in 1985-88, while the number of Arctic terns has decreased by 19 per cent, shags by 16 per cent and fulmar by 15 per cent.
Although overall guillemot numbers have risen by 14 per cent in Shetland since the survey, the RSPB says breeding numbers at its reserve at Sumburgh Head are the lowest since monitoring began in 1977.
Fewer pairs than ever before laid eggs, with no more than eight chicks being reared by the 108 pairs that tried to breed in the study area.
Few if any kittiwake chicks are likely to fledge, while the number of shags has also dropped on last year.
A similar situation exists on Fair Isle with no young guillemots reared and no kittiwakes, Arctic skuas, great skuas or Arctic terns expected to rear. On Foula, Arctic terns did not even lay eggs. Exceptionally low numbers of Arctic skuas were recorded and no young have been reared; great skuas have suffered unprecedented losses of young with few if any expected to fledge; guillemots have failed almost completely.
At the RSPBs Mousa nature reserve, hundreds of Arctic terns arrived in the spring and some laid eggs but no young have been reared; about half the usual number of pairs of Arctic skuas were present and no young were reared; great skuas are expected to rear few if any young.
In Orkney, all the large Arctic tern colonies in the north isles have failed and, for the first time in living memory, none nested at the RSPB reserve on the North Hill of Papa Westray.
Arctic and Great skuas are also having a very poor breeding season and numbers of guillemots and kittiwakes are very low.