The strange story of Ireland's seagulls. Why are they vanishing at such a rate?

They may have earned themselves a bad name in British towns with their aggressive dive-bombing tactics, but in Ireland herring gulls are in severe trouble, with numbers plummeting by 90 per cent.

They may have earned themselves a bad name in British towns with their aggressive dive-bombing tactics, but in Ireland herring gulls are in severe trouble, with numbers plummeting by 90 per cent.

The species has disappeared from the coastline at such a rate that it has been placed on an ornithological danger list. An Irish expert says the population is in "free-fall nationally". Twenty-seven thousand individuals have been lost in the past few decades.

The exact causes of the population decline are unknown; theories from fishing to avian botulism have been advanced.

The bird's plight was laid bare in a 15-year census published by Birdwatch Ireland. Its unpopularity among humans means, however, that any widespread campaign to save it is unlikely.

Ireland has also been relatively untroubled by the urban gull phenomenon which has affected some parts of Britain as birds move into towns and cities. There are only a few small urban colonies scattered along the eastern coast.

Instead, the Irish story has been one of steep decline. Lambay Island off Dublin used to have 10,000 pairs of gulls, today it has just a few hundred. Cape Clear island off Co Cork, which once had more than 500 birds, now has fewer than 50.

Dr Stephen Newton, of Birdwatch Ireland, said: "Because gulls have always been so numerous - and because nobody's worried about them - this has gone on without people really being aware of it.

"It was only when a 15-year census was carried out that this came to light. There has been a decline in Britain as well, but on nothing like this scale. This raises concerns for the herring gull's future."

A large drop in the Dublin area had been expected, since it had been noted that herring gulls had all but disappeared from areas such as the city's Sandymount Strand. That was explained because thousands of gulls on Lambay Island were poisoned in the early 1990s because they were regarded as a risk to aircraft using Dublin airport. That reduced the island's population from 20,000 to 5,000, but two surprises followed. One was that the numbers continued to drop dramatically in the ensuing years, while the other was that they also declined sharply elsewhere around the coast of both the Republic and Northern Ireland.

In addition to the cull and attacks by mink and foxes, three main theories are being advanced for the plummeting numbers. One is that the fishing industry is less active in Irish waters, with quotas and bigger mesh sizes. This means the herring gull has fewer fishy remains to scavenge.

The second is that a general improvement in waste management policies has reduced the amount of food the gulls can rely on from human dumps. Dr Newton explained: "When rubbish is dumped now it is supposed to be covered almost immediately, on environmental health grounds. This means there is less material available to gulls, crows, rats and everything else."

The third reason is avian botulism, a disease arising from a bacterial toxin that the gulls can pick up while foraging at rubbish dumps. In one year, 200 dead or dying birds were observed on Lambay Island.

Dr Newton explained: "This toxin seems to have a disproportionate effect on the very small number of birds left. Essentially it just paralyses them and then they tend to get hypothermia. This is probably all part of this process but we can't really work out what's triggering it."

In Britain, the increased movement of gulls into urban centres has led to forecasts that the herring gull problem is set to worsen over the next decade. In Ireland the gulls face an uncertain future: instead of any prospect of expansion, it seems they will be locked in a battle for sheer survival.