Environmental Engineering Reference
In-Depth Information
up by the British government's Overseas Territories Environment Programme noted, there is “a risk that
these populations will rapidly increase after the removal of rats.” So, in 2013, the rat eradication plan
was augmented by a separately funded mouse-killing trial.
12
When I asked people at the trust about all this, they admitted that mouse eradication in other places
had only a 50 percent success rate. But they were sanguine about the risks to seabirds from a boom in
the mouse population, because “there are no rats present in the areas where mice have been detected, so
removing rats should have no effect on those mouse populations if the mouse eradication is unsuccess-
ful.” Maybe, but equally this suggests that mice live where rats don't, and if the rats are removed while
the mice survive, then the mice may spread. Given the alarming history of super-sized mice eating their
way through the birds of Gough Island, the saga may not be over.
The perils of such efforts to reengineer even simple island ecosystems is shown starkly on Macquarie
Island, another bleak, treeless speck of rock in the Southern Ocean, halfway between Australia and
Antarctica. After being discovered by Europeans in 1810, it was regularly visited by hunters eager to
slaughter its penguins and seals in pursuit of fur and blubber. It also had huge colonies of seabirds. Every
Royal penguin on Earth nests here. Thanks to the human visitors, however, the island soon stocked up
on foreign animals.
First came rats, jumping from the sealers' ships. The rats ate food stores that the sealers left buried
in wooden barrels. So the sealers brought in cats to hunt the rats, and then rabbits as a living larder to be
taken for the pot during their visits. Despite being hunted by both humans and cats, the rabbits enjoyed
the damp and chilly terrain rather too well. By the mid-twentieth century, there were some 150,000 of
them, 2,000 for every square mile of the island, nibbling their way through its tussock grasses.
By then, conservationists were in charge of the island. They decided something had to be done
before the rabbits turned the place into desert. That something would be a flea,
Spilopsyllus cuniculi
(Dale)
, which lives in the fur of rabbits and carries the myxomatosis virus.
13
Introduced in 1968, the
virus cut the rabbit population by 90 percent. The island's vegetation began to recover. But there was
still a problem: the cats. Without rabbits to eat, the cats turned their claws on the island's ground-nesting
seabirds. On Macquarie, as elsewhere, birdlife is conservation's royalty. So, starting in 1985, the Aus-
tralian government started shooting the cats. Many ecologists at the time thought this was a dumb move,
and they were right. Fifteen years later, the island was cat-free. But without the cats, the rats ran riot,
eating the birds in ever-greater quantities. And the rabbits had never gone away. Without the cats, their
numbers also revived dramatically. Their renewed nibbling of the grass began to cause soil erosion, cul-
minating in a landslip in 2006 that buried alive an important penguin and albatross colony.
14
grand plan, costing around $21 million. Everything had to go. They would eradicate rats, rabbits, and
the increasing numbers of mice by mass poisoning using brodifacoum, with any survivors taken out by
follow-up teams of hunting dogs.
16
Sometime in 2012, the dogs finally nailed what were thought to be the last thirteen rabbits. Job done?
Scientists back in Australia, sitting at their screens running computer models of the island's ecosystem,
believe so. But don't hold your breath. For the poison seeped into the soils and vegetation and began
killing hundreds of the birds, including kelp gulls, giant petrels, black ducks, and skuas.
17
The story
seems far from over. Nobody yet knows if the eradications have been achieved.
18
And if rabbits start
popping their heads out of their burrows again, there may be a call to bring the cats back.
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