A killer mouse that has turned from a shy vegetarian into a rapacious, predatory carnivore is being blamed for the worst breeding season on record for a rare albatross.

Tristan albatrosses are found only on Gough Island, a British territory in the South Atlantic, and they are being terrorised by house mice.

Since being introduced to the remote island, the mice have thrived in the absence of predators, and have grown so bold that they attack and eat the albatross chicks.

This year the number of chicks surviving long enough to fly the nest was five times lower than it would have been without the mice. From the 1,764 adult albatrosses found to be incubating eggs in January, only 246 had chicks that grew to fledgelings.

A second critically endangered bird, the Gough bunting, is also under attack by the mice, and the population has halved in the past 20 years to an estimated 400 to 500.

Richard Cuthbert, an RSPB scientist, said: “We’ve known for a long time that the mice were killing albatross chicks in huge numbers. However, we now know that the albatrosses have suffered their worst year on record. The mice do not affect the adult albatrosses, but we know from our work that these are being killed by longline fishing vessels at sea. So unsustainable numbers of this bird are being killed on land and at sea.

“We also know that the mice are predators on the eggs and chicks of the Gough bunting, and mice predation is the main factor.”

Peter Ryan, of the University of Cape Town, said: “Without urgent conservation action to remove the mice, both the albatross and the bunting are living on borrowed time.”

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