The story of the Stephens Island Wren is one of the more predictable parables in the annals of extinction. The wren was a tiny flightless songbird that lived on an island measuring just 150 hectares in New Zealand’s Marlborough Sounds, and it was doomed from the moment it was proposed that a lighthouse be erected there in the late 19th century.
The lighthouse was operational by early 1894. The wren was discovered a few months later, in the jaws of the lighthouse keeper’s cat Tibbles; the species was lost forever by the winter of 1895. As the Christchurch newspaper The Press editorialised at the time, “This is probably a record performance in the way of extermination.”
For years, poor Tibbles was held responsible for nibbling his way through the island’s entire population of wrens. In fact, the island was heaving with feral cats after the accidental escape of a pregnant female in early 1894. It took another three years for them to also kill off the Stephens Island Piopio, a type of thrush.
I’m not sure which scientific or historical literature Adrian Franklin reviewed in his defence of the feral cat – he doesn’t say. Franklin claims detestation of introduced animals is linked to our national paranoia about, wait for it, asylum seekers. This seems rather a long bow to draw, but let’s come back to it later.
Franklin claims these (unnamed) scientists agree that there is no evidence linking feral cats to wild extinctions “apart from a few very exceptional island sites” – a rather cavalier dismissal of the fate of the Stephens Island Wren, but then again, it’s only a Kiwi, and I don’t mean that other flightless bird.
So why, Franklin asks, have cats not been reclassified as harmless animals? Why isn’t the innocent moggy naturalised, as in Britain? (I confess I nearly scratched my own eyes out at this point.)
Firstly, cats don’t act in isolation in the threat they pose to our native fauna. Habitat clearance, disease, grazing, changes to fire regimes, pollutants and, of course, other feral animals all play their parts. I look forward to Franklin’s defence of the fox, Cane Toad, carp, rabbit and non-native rats and roaches.
In Europe, cats, foxes and rabbits have all been part of the natural environment for millennia. That’s not the case in the Antipodes, where there are few land-based top-order predators. Introduced ones have filled the breach. In New Zealand especially, native animals have been annihilated by cats, rats, stoats and possums.
The feral problem is so bad in the Land of the Long White Cloud that many native birds – Kokakos, Kakapos, Saddlebacks and others – are now largely confined to or have themselves been introduced (at considerable public expense) to islands where foreign predators and competitors aren’t waiting to devour them.
The picture is no prettier in Australia, where we hold the world record for mammalian extinctions: 22 have been extirpated since European settlement, with over 100 more considered endangered. Cats and foxes have played a determining role in most of these. The proof can be found in Tasmania, which mostly retains its mammalian diversity (aside from the elimination of its biggest top-order predator, the Thylacine).
Until their recent accidental or malicious introduction, foxes have not existed in the island state, and Tasmanian Devils – the largest surviving marsupial predator – have probably kept a lid on feral cat numbers. The Tasmanian government has spent a fortune trying to suppress the foxes; it will need to, especially given the crash of the devil population due to facial tumour disease.
On the mainland, predator-free sanctuaries, such as those at Scotia in western NSW, are reintroducing quaintly-named animals like the Bilby, Boodie, Woylie and Numbat. Such sanctuaries may be their only hope. At Currawinya National Park in south-west Queensland, cats destroyed one of the last remaining wild colonies of Bilbies last year after a protective fence was found to have rusted.
In Arnhem Land, the Australian Wildlife Conservancy recently conducted an experiment with the near-threatened Pale Field Rat. The rats have been regionally extinct in Arnhem Land for years and had to be sourced from – surprise, surprise – predator-free Quoin Island off the Northern Territory coast.
The AWC set up two 10-hectare enclosures. One was secured with an electrified six-metre fence, the “control” enclosure was not. Twenty rats fitted with radio collars were introduced into each. Within a week of two cats finding the unsecured enclosure – captured on film by motion sensor cameras – the rats were gone.
I’m still not sure what all of this has to do with our national xenophobia over immigration. Perhaps, as one wag suggested on the Australian birdwatching forum Birding-Aus, when asylum seekers start eating us, Professor Franklin may have a point.
First published in The Age, January 13 2013