Giant carnivorous mice threaten world's greatest seabird colony

John Vidal, The Guardian 19 Jan 08;

Whalers who visited remote Gough Island in the South Atlantic 150 years ago described a prelapsarian world where millions of birds lived without predators and where a man could barely walk because he would trip over their nests. Today the British-owned island, described as the most important seabird colony in the world, still hosts 22 breeding bird species and is a world heritage site.

But Gough is the stage for one of nature's greatest horror shows. One of those whaling boats, probably from Britain, carried a few house mice stowaways who jumped ship on Gough. Now there are 700,000 or more of them on the island, which is the size of Guernsey.

What is horrifying ornithgologists is that the humble house mouse which landed on Gough has somehow evolved to two or even three times the size of an ordinary British house mice, and instead of being a vegetarian, eating insects and seeds, has adapted itself to become a carnivore, eating albatross, petrel and shearwater chicks alive in their nests. They are now believed to be the largest mice found anywhere in the world.

Those who have witnessed the phenomenon say that the supersized mice attack at night either on their own or in groups, gnawing through the nests and into the baby birds' bodies. Their parents, who have never experienced predators, are unable defend their offspring from the rodents' furtive attacks.

Yesterday, Birdlife International, a global alliance of conservation groups, recognised that the mutant mice, who are without predators themselves, are now completely out of control and are threatening to make extinct several of the world's rarest bird species.

The organisation, which runs the Red List of endangered bird species, raised both the Tristan albatross, of which only a few remain in the world, and the Gough bunting, a small finch found nowhere else in the world, on to the list of the world's most critically endangered species, the highest category of threat. Five other bird species on the island are also said to be threatened.

"Things are getting worse on Gough. In the presence of house mice, the albatross and bunting have no chance of survival. The only hope for these threatened birds is the complete eradication of mice", said Dr Geoff Hilton, an RSPB scientist who has been researching conservation problems in UK overseas territories.

"The world's greatest seabird island is being eaten alive, as the mice are likely to be affecting the fortunes of many seabirds on the island. Without help, Gough Island will be likely to lose the majority of seabirds," said Hilton.

Studies suggest that about 60% of all Gough's bird chicks die in their nests, probably because of predation by the mice. "It is a catastrophe. The albatross chicks weigh up to 10kgs. Ironically, they evolved on Gough because it had no mammal predators - that is why they are so vulnerable. The mice weigh just 35g; it is like a tabby cat attacking a hippopotamus", said Hilton.

Yesterday, the RSPB proposed hiring helicopters to drop thousands of tonnes of rodent poison on the island. "A government-funded feasibility study done with New Zealand, which has eradicated rats from many islands, shows it is possible. They mice would take the poison and just go to their nests and die. We think it could be done fairly easily and would cost about £2.6m", said a spokeswoman.

"The study shows there is a glimmer of light showing that we might be able to fix this problem. The UK government has supported us in discovering the problem, in conducting the feasibility study, and now in finalising our plan for the mouse eradication. The big question is whether the UK will take its international commitments seriously and do what the governments of New Zealand and Australia have done, and provide the big money needed to actually do the mouse eradication. If they don't, we won't be able to give two critically threatened species the lifeline they need"

Britain has long been criticised for not maintaining the ecology of its overseas territories which are mainly made up of groups of islands like Pitcairn, Tristan da Cunha, and the Falklands. Of the world's 190 most endangered birds, 32 are now officially British responsibility.

The discovery that the mice had supersized themselves and adapted their diets was made by Richard Cuthbert, a professional ornithologist who spent a year on the island in 2001 and only stumbled on the phenomenon as he was leaving the island. "It sounds incredulous, implausible that a mouse could attack a chick, but these chicks are really big spherical balls of fat covered in down, and because they are so fat and big they cannot defend themselves", he said later.