The island of Lundy, in the Bristol Channel. Photograph: Robert Harding Picture Library/Alamy
A project to eradicate rats from a rocky island off Devon has resulted in a tenfold increase in the population of an endangered burrowing seabird that nests there, conservationists have revealed.
Wildlife charities are delighted that the removal of rats from Lundy, in the Bristol Channel, has apparently led to a dramatic boost to the number of Manx shearwaters and other birds on the island.
A similar project costing £750,000 is due to get under way this autumn on two of the isles of Scilly, St Agnes and Gugh, to wipe out the descendants of brown rats that swam to shore from shipwrecks.
But while residents and bird lovers are celebrating the success on Lundy and the plans for Scilly, some animal rights activists are angry that rats are being killed. They accuse those behind the cull of targeting the rodents to boost the tourist industries on the islands, which depend to a large extent on birdspotters.
Survey teams from the RSPB who returned to Lundy 10 years after the launch of the seabird recovery project found that the number of breeding pairs of Manx shearwaters had leapt from 300 to 3,000. Puffin numbers had increased from just five birds to 80, while razorbills and shags had also made substantial gains.
Helen Booker, RSPB senior conservation officer in the south-west of England, said: “This is such an exciting result, better than we expected, and the rate of increase is an indication of just how important rat-free islands like Lundy are as breeding site for seabirds.”
David Bullock, head of nature conservation for the National Trust, which owns Lundy, said “Once the rats had gone from Lundy, the number of pairs of shearwaters went from hundreds to thousands in matter of a few years.”
He said such a rapid recovery must have been aided by birds from other colonies, probably including those on islands off the Pembrokeshire coast, settling to breed on Lundy.
The results will provide encouragement for a similar project on St Agnes and Gugh, 28 miles off the south-west tip of mainland Britain. Here an estimated 3,100 brown rats are blamed for preying on Scilly shearwaters as well as storm petrels, terns and the Scilly shrew, a rodent found only on the archipelago.
From this autumn, poison bait will be laid for the rats as part of a 25-year Isles of Scilly seabird recovery project, which is being run with cash from the National Lottery, the EU’s Life fund and other sources.
It follows a 25% fall in bird numbers in recent years. The project is deemed feasible because the islands are surrounded by deep water, and so it is thought unlikely once the rats there are removed that others will be able to repopulate it.
It is deemed particularly important because St Agnes and Gugh are close to the uninhabited island of Annet, which has significant colonies of seabirds.
Jaclyn Pearson, project manager for the Isles of Scilly recovery project, said it had the backing of the 75 residents of St Agnes, though some of the children had taken some convincing.
She said the bait stations were designed to be accessible only to rats, and a stock of the antidote had been ferried across in case a cat or dog got to the poison. The islanders will cull the extra rabbits likely to be hopping around once the rat population decreases.
The Animal Aid campaign group accused the Lundy and Scilly projects of condemning rats to an “awful death” for commercial reasons. It suggested that other factors – including too many tourists – could be causing the falls in seabird numbers.
Its director, Andrew Tyler, said: “Rats don’t sell tourist tickets but birds do. They are making a judgment that the birds are important and rats are disposable. We do not accept that premise.”
• This article was amended on 30 July 2013 because the original called Animal Aid a charity. This has been corrected.