One of the lessons that evolution teaches us is that you really shouldn’t release alien species onto remote, isolated islands (or other such isolated habitat). This is because 1) these places often contain unique species that have evolved to fit their particular, often predator-free locale. And 2) newly introduced species, finding abundant prey and few of their own predators, are likely to run amok, quickly adapting to local conditions and killing everything in sight. If you care about biodiversity, keep the aliens away.
Unfortunately, we’ve got this kind of problem on our hands in the South Atlantic. While the victims of the feast are not some flightless, defenseless animal that’s been living in paradise too long, they are mostly dependent on one particular island for nesting, meaning that the sudden predation they’re suffering could threaten them with extinction. And the best part is, the perpetrators are… house mice! Mice that have quickly evolved to 3 times their normal size, and have recently started taking on prey that is much, much larger than themselves, acting extremely aggressive and voracious. If not for the threat this poses to endangered sea birds, this would actually be cool. Here is the story :
“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.
The image of rapacious packs of killer house mice devouring prey which dwarfs them in size is really too much. I don’t think I’ll be sleeping well tonight.