Despite misleading figures published by news agencies about the rodents eating one million seabirds each year, the threat is real. The projections are for example that the current 1.8m breeding pairs of petrels could be reduced by 50% over the next sixty years because of incredible attacks by predatory mice.
Gough Island, a world heritage site in the South Atlantic, is probably the most important seabird colony in the world with more than ten million birds. The island hosts 99 per cent of the world’s Tristan albatross and Atlantic petrel populations - the birds most often attacked by the overgrown mice. Just 2,000 Tristan albatross pairs remain.
An RSPB-supported research team which included Ross Wanless who did work on Aldabra, found that the house mice, three times the size of those normally found in Seychelles, attack at night. There are about 700,000 mice, which have somehow learnt to eat chicks alive, a behavior not found in mice elsewhere.
The chicks weigh up to ten kilograms, are nearly a metre tall and 250 times the weight of the mice but are largely immobile and cannot defend themselves. The mice weigh just 35 grams; it is like a tabby cat attacking a hippopotamus, Geoff Hilton of the RSPB told me.
Scientists suspect that the mice are also eating the eggs and chicks of the rare, ground-nesting Gough bunting, a small bird endemic to Gough. This species is one of the most worrying because there is no other population in the world.
Cousin and Cousine are the only seabird islands in Seychelles that are both rat and mice free. Important seabird islands like Bird and Aride do have mice and an obvious fear is that the rodents could start behaving like those on Cough.
This is of concern to the management of other islands where rats (but not mice) have been successfully eradicated recently and are in the process of island restoration by introducing rare birds. Birds like the Seychelles Magpie robin, Warbler and Fody may be vulnerable to “super mice”.
It is well known that flora and fauna can evolve to large sizes on isolated islands. Giant tortoises are a good example. However, this usually takes hundreds of thousands to millions of years, ending up with new species. In cold environments, like on Gough island, growing to a larger size in a much shorter time may be more common and more adaptive for small animals like mice.
Whatever the case may be, the last thing we want after spending so much money and effort ridding islands of rats is a new problem with predatory mice.
By Nirmal Jivan Shah, published on The People Newspaper on 28th July 2005