If you own one of the 3.3 million pet cats in Australia, spare a thought for the 75 million native animals that die every night at the claws of their feral cousins (believed to number between 10 to 20 million). These ruthless killers are a hot political topic, with Federal Environment Minister Greg Hunt last year announcing a 10-year plan to eradicate “all the significant populations of feral cats around Australia”.
But although culling feral cats might sound attractive, we need to think holistically about any knock-on effects removing them may have, says Tim Doherty, whose research into feral cats is forming the basis of his PhD at Edith Cowan University in Perth.
Feral felines are the same species as an ordinary house cat – only bigger. One massive specimen shot in Gippsland, Victoria, in 2008 measured 176 centimetres from nose to tail tip. Their size means they’re able to catch larger prey than a pet cat can tackle – up to 5.5 kilograms. More than 400 vertebrate species are on their menu in Australia, including at least 16 globally threatened species.
To date, feral cats have wiped out at least 22 mammal species. “Cats are enemy number one for mammal conservation in Australia,” Doherty says. But the first step to eradicating them is figuring out where they sit in Australia’s ecosystem.
Doherty’s research has focused on the habitat and diet of feral cats. He performs field experiments at the Charles Darwin Reserve, a 686-square-kilometre patch of land 355 kilometres northeast of Perth, trapping feral cats and looking at their scats to determine where they live and what they eat.
New research suggests that dingoes, as a top predator, may actually suppress and exclude feral cats from certain areas.
The most important message to emerge from Doherty’s research is that pest control must take into account all species – not only feral cats. The relationship between feral cats and another pest – rabbits – is a perfect example. Doherty found that where cats could feed on rabbits they ate fewer native mammals. So by eradicating rabbits, you run the risk of the cats switching prey. Conversely, when feral cats were culled from Macquarie Island from 1985 to 2000, rabbit numbers exploded and threatened to devastate the World Heritage-listed island, prompting a huge follow-up program to eradicate the rabbits as well.
Feral cats are having the biggest impact in northeastern Australia. Since the early 1990s, small and medium-sized mammals such as the northern quoll have severely declined in places such as Kakadu and the Kimberley, says Doherty. He says inappropriate fire management and grazing practices are helping the cats by removing the grass cover that protects native mammals. The Australian Wildlife Conservancy has used GPS collars to show that feral cats will head in a straight line towards freshly burnt or grazed areas and decimate the native mammals there, Doherty adds.
So what’s the best way to control feral cats? Enter the dingo. In some areas, feral cat numbers are inversely correlated with dingo populations – that is, where you find many dingoes there are fewer cats (and the other way around).
“There’s a lot of new research suggesting that dingoes, as a top predator, may actually suppress and exclude feral cats from certain areas,” Doherty says. Dingoes tend to prey on larger, more plentiful animals such as kangaroos, rather than threatened small mammal species. In fact, a study published in February advocates for dingoes to be reintroduced into some areas to measure their impact on feral cats. But people’s perceptions of dingoes remain polarised – some farmers don’t like them because they can kill livestock.
While we work out where and how to remove feral cats, Doherty suggests establishing “insurance populations” of threatened species, either by placing them on predator-free islands or within fenced mainland reserves.
In the meantime, he plans to keep digging into the hidden habits of Australia’s most efficient hunter. “There are lots of studies on controlling feral cats, but certain things like their habitat use are not well-understood,” he says. “There is no one-size-fits-all response either. In one part of the world cats might like forests but avoid grasslands, and it might be in the inverse in another area.”
This story was sponsored by Edith Cowan University