From Mice To Penguins
As 92 year-old David Attenborough launches his namesake polar ship, popularly known as ‘Boaty McBoatface’, I’m reminded that planet management never gets easier.
On the island of Macquarie, between Australia and Antarctica, problems started soon after it was discovered in 1810. The island’s fur seals, elephant seals and penguins were killed for fur and blubber, but it was the rats and mice that jumped from the sealing ships that started the problem.
Cats were introduced to keep the rodents from food stores. Rabbits followed some 60 years later, as part of a tradition to leave the animals on islands to give shipwrecked sailors something to eat.
Given easy prey, cats feasted on the rabbits and feline numbers quickly grew. The island then lost two endemic flightless birds, a rail and a parakeet. The rabbits bred rapidly and ate the island’s vegetation.
By the 1970s, some 130,000 rabbits were causing so much damage that myxomatosis was the latest foreign body introduced to Macquarie, which took the rabbit population down to under 20,000 within a decade.
The island’s vegetation then began to recover, but what was good for the vegetation proved bad for the island’s wildlife. With fewer rabbits around, the cats turned to local burrowing birds. By 1985, conservationists deemed it necessary to shoot the cats.
The last cat was killed in 2000, but the conservationists were horrified to see rabbit populations soar. Myxomatosis failed to reduce them and the newly strong rabbit population quickly reversed decades of vegetation recovery. Without vegetation roots, the soil shifted. In 2006, the rabbits were blamed for a massive landslip that wiped out much of an important penguin colony.
From mice to penguins – the chain of events is a rare example of ‘trophic cascade’ leading to ‘ecosystem meltdown’.