Killer Mice On The Loose

Mother petrel birds on Gough Island have a serious concern on their hands. Their young are being ravaged by strangers introduced to the island 150 years ago. House mice, which have grown far larger than they are normally, are massacring up to 75% of their chicks - and it looks like there's no end in sight.

This phenomenon is so severe that researchers are afraid that the birds might actually be wiped out.

"The sheer densities of the numbers of birds there-that's why Gough Island is so special. But the mice seem to be chewing away through those," commented co-author of the paper, Ross Wanless from the University of Cape Town to the National Geographic.

Gough Island is an important nesting ground for Atlantic seabirds. The island hosts up to ten million birds of more than 20 species - and not all of them are safe. Studies have shown that even the giant, endangered Tristan albatross has fallen prey to these super mice.

The mice on Gough Island have grown to more than 50% their size, putting them at approximately ten inches long without the tail. The mice, at 1.2 ounces, are so hungry that they are able to overcome the baby petrel and the much larger baby albatross, which can weigh up to 22 pounds. In other words, the albatrosses are about 300 times larger than the mice.

In Wanless's words, "Essentially, these are babies. If you put an extremely hungry rat in a room with a human baby, [the infant] wouldn't be able to defend itself."

The mice have no predators on the island and have bred mercilessly. There are around 300 of them per hectare, putting about 1.9 million mice on a 25 square mile island.

The study was done over four breeding seasons by Wanless and his colleagues. They used infrared cameras to monitor 178 petrel nests for any invading mice and checked up on the nests once a week.

"If this has been going on at this rate for 150 years, which is entirely possible, there could have been 30 million pairs of Atlantic petrels" before mice were introduced, Wanless said.

Petrels used to breed on another island in the South Atlantic, Tristan de Cunha, however, researchers believe they were wiped out by black rats.