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Gangs of mice are eating seabird chicks alive on a remote Atlantic island
It is estimated that mice are killing up to two million chicks per year on Gough Island, threatening the survival of many endangered seabirds.
Gough Island - located in the middle of the southern Atlantic, far from any major land mass - is listed as a UNESCO World Heritage site due to its pristine environment.
But for the last two decades, scientists monitoring the millions of seabirds living on Gough Island have realised that all may not be as it seems. In the dead of night, they have uncovered a series of gory events.
As the Sun sets on the breeding colonies of birds, an ominous threat emerges from the undergrowth.
At two times larger than normal, the mice on Gough Island have grown into giants.
They've also developed a taste for blood.
The mice seek out the chicks of seabirds and start to eat away at their flesh. So pervasive are these invasive rodents that a new paper published this week in the journal IBIS estimates that every year a staggering 1.7 million chicks are killed by the mice.
Seabirds nest all over Gough Island's rugged landscape © Ben Dilley/RSPB
Dr Alex Bond, a Senior Curator of Birds at the Museum and co-author of the new study, says 'It is absolutely shocking.
'We've observed mice attacking Tristan albatross chicks, where the rodents will eat through the body wall near the rump of the bird while they are still alive. It can take up to four days for the chicks to die.'
No natural predators
Located some 2,800 kilometres from South Africa to the east and 3,200 kilometres from South America to the west, Gough Island is one of the most remote islands in the world.
This splendid isolation is an ideal nesting ground for a whole host of seabirds free from predators. It is currently home to some 22 species of seabirds and two species of landbirds that breed right across the rugged terrain.
These include rare species such as and the endangered Atlantic petrel and the critically endangered Tristan albatross. And there are also many endemic species on the island such as the Gough finch and the MacGillivray's prion, which means that they are found nowhere else in the world.
The mice, however, are not native to Gough Island. Introduced at some point in the mid-nineteenth century by passing boats, they have rapidly spread over the entire site as their population boomed.
The rodents predate a wide variety of seabird chicks, many of which are close to extinction © Peter Ryan/RSPB
But they have no natural predators, which leaves the chicks vulnerable.
This means that a single mouse weighing just 30 grams can kill an albatross chick that weighs 10 kilograms.
It has also been found that sometimes the mice will travel around in gangs. 'You can see up to eight or nine mice attacking a single albatross chick, but typically they forage alone,' says Alex.
'The chicks simply have not evolved the behavioural defences. An albatross has a lifespan of 60 years, and so if you look at in evolutionary terms it is going to take a long time for new behaviour to come into that population.'
By looking at the number of chicks that are successfully raised on Gough Island from a selection of species, and the comparing them to other predator free colonies, the researchers could estimate that in just a single year 1.7 million chicks are killed by mice.
For an island with around four million breeding pairs of seabirds, the predation has been catastrophic. In some years, for example, the MacGillivray's prion has failed to raise a single chick, while up to 70% of the Atlantic petrels' young are lost to the mice.
If nothing is done, many species will simply go extinct.
The RSPB plan on dropping rat poison right across the island using two helicopters © Ben Dilley/RSPB
Rodent eradication
The Royal Society for the Protection of Birds (RSPB) is planning a programme to eradicate every single mouse from Gough Island by 2020. This will involve using helicopters to drop poisoned bait across the entire island.
'The helicopters fly a very precise and intricate pattern across the island twice over a period of six weeks dropping the rodenticide,' says Alex. 'The idea is that you do two drops within a very short window and that will get rid of the mouse problem.'
While this sounds deceptively simple, it has taken years of planning to get to this stage, and the logistics of doing so in such a remote location are huge. But the results will be worth it.
Having already been carried out on almost 700 islands before, the scientists can be sure that the poison will have no adverse effects.
It is hoped that within just one year the entire island will be completely mouse-free for the first time in generations, giving the seabirds back a safe place to raise their young.
