July 26, 2005
Rare Island Birds Threatened by ‘Super Mice’
JOHANNESBURG -- "Monster mice" are eating meter-high albatross chicks alive, threatening rare bird species on a remote south Atlantic island seen as the world's most important seabird colony. Conservation groups say the avian massacre is occurring on Gough Island in the South Atlantic, a British territory about 1,600 kms (1,000 miles) southwest of Cape Town and home to more than 10 million birds.
"Gough Island hosts an astonishing community of seabirds and this catastrophe could make many extinct within decades," said Dr Geoff Hilton, a senior research biologist with Britain's Royal Society for the Protection of Birds (RSPB)."We think there are about 700,000 mice, which have somehow learned to eat chicks alive," he said in a statement.
The island is home to 99 percent of the world's Tristan albatross and Atlantic petrel populations -- the birds most often attacked. Just 2,000 Tristan albatross pairs remain.
"The albatross chicks weigh up to 10 kg (22 lb) and ... the mice weigh just 35 grams; it is like a tabby cat attacking a hippopotamus," Hilton said.
The house mice -- believed to have made their way to Gough decades ago on sealing and whaling ships -- have evolved to about three times their normal size.
This is a common phenomenon on island habitats -- for reasons much debated among scientists -- where small animal species often grow larger while big species such as elephants display "dwarfism" and become smaller.
In the case of the mice of Gough Island, their remarkable growth seems to have been given a boost by a vast reservoir of fresh meat and protein.
The rapacious rodents gnaw into the bodies of the defenseless and flightless chicks, leaving a gaping wound that leads to an agonising death. Scientists say once one mouse attacks the blood seems to draw others to the feast.
While predation by oversized mice is unusual, birds on small islands are especially vulnerable to extinction from human activities such as the introduction of alien species.
This is because many birds that have evolved on isolated islands with no predators have become what biologists term "ecologically naive" -- meaning they do not recognize danger from other animals.
Flightless species -- or chicks that cannot yet fly -- are especially at risk. The predatory nature of the mice was confirmed by researchers from the RSPB and the University of Cape Town.
The ground-nesting Gough bunting, a small finch found nowhere else in the world, is also at risk.
Gough Island is the most southerly of the Tristan da Cunha group. There are 22 bird species nesting on the island of which 20 are seabirds.