Flesh-eating Mice, the Tristan Albatross and looming extinction

House Mouse and Albatross chick. Pic. Ross Wanless

The sorry story of the Tristan Albatross Diomedea dabbenena and the depredations caused by a feral population of the House Mouse Mus musculus on Gough Island in the south Atlantic has been around for a few years.

I first saw reports about this aberrant Mouse behaviour in about 2005 and have been keeping a watching brief on it for a while.

As the UK Telegraph noted in 2007, quoting my colleague, Ross Wanless of the Percy Fitzpatrick Institute at the University of Cape Town:

“…about 1,000 endangered Tristan Albatross chicks – about 70 per cent of all those born – are being taken by the mice.

The island, a British territory 1,700 miles off the coast of South Africa, is the breeding ground for almost the entire world population of these rare birds. The scale is sufficient to drive extinctions,” said Ross Wanless, an ornithologist at the University of Cape Town, who has been researching the killer mice. “We had no idea that mice could do this sort of thing.”

Swarms of 10 mice at a time can be seen gnawing at the chicks’ bodies until they eventually die through blood loss or destruction of vital organs. Chick carcasses found later are reduced to little more than skin and bones. An albatross chick weighs more than 20lb, about the size of a goose, while a mouse weighs just two ounces.”

Now a new report from the international bird conservation group BirdLife International has found that the mice are decimating the by now Critically Endangered Tristan Albatross population on Gough Island.

The mice are also affecting Gough Island’s other Critically Endangered endemic species, the Gough Bunting Rowettia goughensis. The BirdLife International report notes:

“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”, said Richard Cuthbert, an RSPB scientist who has been researching the mice problem on Gough Island since 2000. “We also know that the mice are predators on the eggs and chicks of the Gough bunting and mice predation is the main factor behind their recent decline.”

A complete survey of the Tristan Albatross on Gough Island in January showed there were 1764 adult albatrosses incubating eggs. A later survey revealed that only 246 chicks had survived to fledging.

This is evolution in action – the mice have fundamentally changed their behaviour:

Geoff Hilton, another RSPB research biologist. “We think there are about 700,000 mice, which have somehow learnt to eat chicks alive – much like blue tits learnt to peck milk bottle tops. The albatross chicks weigh up to 10kg and, ironically, albatrosses evolved to nest on Gough because it had no mammal predators – that is why they are so vulnerable.

Mr Wanless said: “There are mice on other South Atlantic islands but Gough is the only site where this is known to be happening. Once one mouse has attacked a chick, the blood seems to attract others. They gnaw into the chick’s body, create a gaping wound and the chick weakens then dies over several days.”

And they have dramatically increased in size – a typical House Mouse in the UK and elsewhere (think of your kitchen!) weighs in at about 15 grams – the monsters on Gough Island weigh between 27g and 40g.