A giant ecosystem that has functioned for millions of years has begun to break down

They are disaster zones: professional ornithologists who have spent their careers monitoring the teeming, screaming bird life of Orkney and Shetland have never seen anything like it.

They are disaster zones: professional ornithologists who have spent their careers monitoring the teeming, screaming bird life of Orkney and Shetland have never seen anything like it.

On cliff ledges, on moorlands, on shingle banks, the nesting attempts of hundreds of thousands of seabirds in Scotland's Northern Isles have come to grief in the summer of 2004.

It is the year without young. Eggs have not been laid; where eggs have been laid, they have not hatched; where they have hatched, the chicks have died in the nest, and the tiny numbers of chicks that have left the nest have not lasted long.

A giant ecosystem that has functioned for millions of years has broken down. The reason is starvation, and the reason for the starvation is thought to be climate change: this is a taste of things to come.

There have been seabird nesting failures in the Northern Isles before, but the extent of this year's catastrophe is entirely unprecedented.

On the island of Papa Westray in Orkney, for example, only five of the 85 nests of kittiwakes had chicks earlier this month. On the island of Foula, which has the world's largest colony of great skuas, scientists checking a representative sample of 400 nest sites found just two chicks, which were thought unlikely to survive.

At a cliff near Sumburgh Head on Shetland's southern tip, where 1,200 pairs of guillemots assembled to breed in the spring, not a single chick has been produced.

Arctic terns, of which the last census in 2000 recorded 24,716 breeding pairs in Shetland, have produced no chicks at all in the south of the islands, according to Peter Ellis, the local representative of the Royal Society for the Protection of Birds. "In the whole of Shetland they have produced just a handful," he said.

The story has been repeated right across both archipelagos and has a brutally simple immediate cause: starvation. The once-teeming stocks of sandeels, the small fish on which nearly all the local seabirds depend, have vanished, leaving the parent birds unable to feed their young - or even themselves. But behind the sandeels' disappearance is a more sinister cause, threatening us all as well as the seabirds: global warming.

Scientists believe the steadily rising temperature of the water in the North Sea, which has gone up by two degrees centigrade in 20 years, is having a calamitous effect on the sandeels, essentially a cold-water species. After several years of decline, they have vanished almost completely in the waters around Orkney and Shetland.

There is nowhere else in Britain where seabirds are so much part of the landscape, and the economy. The abundance of gulls, terns, skuas, guillemots and puffins has long been a prime tourist attraction, as well as of global wildlife significance. Shetland alone is thought to house 10 per cent of our eight million seabirds, and birders are the principal visitors heading for the treeless, windswept islands to see species they could not find elsewhere in Britain. Suddenly, all this is at risk.

Martin Heubeck of Aberdeen University, who has recorded seabird breeding 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 fact that guillemots are suffering shows the extent of the fish famine. Arctic terns and kittiwakes can only catch sandeels near the sea's surface, but guillemots can fly many miles in search of sandeel shoals and then dive to depths of more than 300ft to catch them. But now they are returning with empty beaks and stomachs.

The great skuas, known locally as bonxies, which live by stealing fish from smaller birds, are displaying disturbing behavioural changes. Not only are they killing and eating the seabirds they would have robbed in the past, but the crisis has even led to cannibalism, with adults eating their neighbours' young. That is another reason why, in many of the colonies, no young birds at all are expected to survive.

Due to the sandeel shortage, the Shetland Fishermen's Association has made an agreement with RSPB Scotland and Scottish Natural Heritage. This year the fishery was closed in the south of Shetland, and although a small fishery was permitted in the north of the islands, no fishing has taken place.

UNDER THREAT

Arctic Tern

Suffered in past from sandeel shortages caused by over-fishing, but this year suffered worse than ever. The 2000 census recorded 24,716 pairs; this year produced virtually no young.

Great Skua

The world's most important populations of this big predatory seabird are on Orkney and Shetland. More than 6,800 pairs on Shetland in 2000 census: a 'handful' of chicks produced this year.

Arctic Skua

There were 1,120 Shetland pairs recorded in 2000. This year there were no surviving young, partly because of starvation, and partly because starving great skuas are eating their chicks.

Guillemot

Can fly long distances and dive very deep so its failure to breed this year means that its food has disappeared over a wide area. Recent census recorded 172,000 pairs in Shetland.

Kittiwake

A small and elegant gull which typically feeds in groups on the sea surface. Recent census recorded 16,700 pairs in Shetland; breeding failure this year 'almost complete'.

Puffin

Puffins are the unknown factor in the breeding crisis. They depend on sandeels more than any other species. But because they nest deep in burrows, the actual position is not yet known.