Far from land in the sub-Antarctic region of the Indian Ocean lie the Prince Edward Islands. There are just two small islands in the group – Prince Edward Island and Marion Island – and the only human inhabitants are the South African National Antarctic Program’s staff at a research station.
After intermittent occupation by sealers, wreck hunters and those collecting guano for fertilizer, the islands were claimed by South Africa in 1947 and the research station was established on Marion Island, a rocky volcanic peak around 19 km (12 mi) long and 12 km (7 mi) wide, surrounded by towering cliffs.
When the new buildings suffered a mouse infestation, a simple solution was adopted. In 1949 five domestic cats were imported to see off the unwelcome rodents; but someone forgot to have them neutered. The consequences were disastrous. Within 30 years there were 3,500 feral cats on Marion Island, feasting not on mice but the very birds the scientists were there to study.
The fearsome felines were particularly fond of petrels, burrowing birds that were easy meat in the breeding season. Some species became extinct on Marion Island and it was only a matter of time before they all went, with even penguin and albatross chicks suffering severe depredation.
It had to stop, and stop it did – not in the kindest of ways. In 1977 a specific feline virus was introduced, wiping out most of the cat population, and thereafter resistant animals were culled by trapping and night shooting. By the mid 1990s the cats were gone, though some suggest a few hardy moggies may still lurk in hidden corners.
The unintended consequences of introducing non-native animals to a balanced natural habitat were plain to see, but in this case it was ultimately possible to limit the damage. It isn’t always so.
Where: Marion Island, Indian Ocean
Death toll: innumerable seabirds that perished as a result of feline predation
You should know: One of the more unusual – unique, actually – sights the researchers on Marion Island have seen was a seal trying to mate with a penguin, which just goes to show there’s no accounting for taste… even in Nature.