LONDON, England (CNN) -- -- Predatory mice are critically threatening the albatross population on a remote South Atlantic island and have caused the birds' worst nesting season on record, a British bird charity said Thursday.
Tristran albatross chicks are in danger from non-native house mice.
The research from the Royal Society for the Protection of Birds indicates bad news for the Tristan albatross, whose only home is Gough Island in the middle of the South Atlantic.
House mice not native to the island are threatening the Tristan albatross with extinction, the RSPB said.
The mice are also threatening the native population of bunting, one of the world's largest finches, the RSPB said.
"Without removal of the mice, both the albatross and the bunting that live there are doomed to extinction," Grahame Madge, a conservation spokesman for the RSPB, told CNN.
The mice on the island eat the chicks of the albatross and bunting before they make it to the fledgling stage, the RSPB said.
This makes it especially difficult for the albatross population to survive because the birds lay eggs only once every two years -- a very low reproductive rate compared to other birds, Madge said.
"What (the mice) are affecting is ability of the albatross to produce enough young to sustain the population," he said.
Adult Tristan albatross are threatened by longline fishing at sea, a practice in which boats put up numerous 100-meter-long fishing lines baited with squid or fish. The albatrosses are attracted to the bait and while some manage to steal it successfully, many more get snagged and drown, Madge said.
Because of the impact from house mice, introduced to the island by sealers in the 18th and 19th centuries, conservation alliance BirdLife International earlier this year listed both the Tristan albatross and the Gough bunting as critically endangered -- the highest threat level before extinction.
Gough Island, a British territory almost midway between Argentina and South Africa, is a place of stunning natural beauty. Its green mountain slopes, topped with snow at its highest points, stretch into the deep blue sea.
The island is not inhabited by humans. Gough Island and nearby Inaccessible Island are both listed as UNESCO World Heritage sites.
A survey of the albatross on Gough Island in January showed 1,764 adults incubating eggs, the RSPB said. A later survey revealed only 246 chicks had survived to fledgling.
"We've known for a long time that the mice were killing albatross chicks in huge numbers," said RSPB scientist Richard Cuthbert, who recently visited the island to assess the problem. "However, we now know that the albatrosses have suffered their worst year on record."
The bunting suffer because the mice eat their eggs and chicks, and may also compete with them for food in the winter, Cuthbert said.
"The decline in bunting numbers is alarming," said Peter Ryan of the University of Cape Town, who has been studying buntings on the island since the 1980s. "Without urgent conservation action to remove the mice, both the albatross and the bunting are living on borrowed time."
The RSPB has been studying whether it is possible to remove the mice. It said trials so far look promising, but it urged the British government to step up funding for the project. It said eradicating the mice from Gough Island would solve the primary conservation threat facing both bird species.
The RSPB said it has been working with New Zealand conservationists on a program to remove the smaller mice by dropping poisoned bait from helicopters.
Tristan albatrosses are one of 22 species of albatross in the world. Albatrosses principally live in the southern Atlantic but some also live in the northern Pacific, the RSPB says.
Albatrosses are among the largest flying birds, weighing up to 25 pounds (22.5 kilograms). One species -- the wandering albatross -- has a wingspan of 11 feet, the RSPB says.
The birds can fly thousands of miles without a pause, and their only need to touch land is to nest and raise their young, the RSPB says.
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