Domestic cats have become notorious in recent years as one of the most destructive invasive species on the planet, now threatening dozens of bird and mammal species with extinction. (That’s on top of the 30 or so species they have already eradicated.) When conservationists are trying to restore a threatened species to its old habitats, a single murderous cat can be enough to destroy the entire project.
Now frustrated scientists in Australia are proposing to apply criminal forensics and even a poison pill to identify and eliminate problem cats—and possibly spare other cats that are innocent of the killing. In an article in the journal Biological Conservation, they call these experimental techniques “predator profiling.”
A team of researchers led by ecologist Katherine Moseby at the University of Adelaide looked at restoration attempts for what they call “challenging species.” That generally means mammals that are big enough, toothy enough, or just plain mean enough that you might not think the average outdoor cat would pose a threat. Many of these species—the western quoll, the burrowing bettong, the rufous hare-wallaby—are largely unfamiliar outside Australia, and that’s the point. They are endemic species found nowhere else in the world and an essential part of Australia’s natural heritage. Cats, introduced to Australia about 200 years ago, aren’t—and they have proved capable of killing native species weighing as much as 12 pounds.
The cats have become a nightmare for restoration biologists. In one reintroduction attempt, 13 of 31 rufous hare-wallabies quickly vanished, and feral cats seemed to be the culprit. The researchers trapped and euthanized a single 11.2-pound cat, and the killing stopped. The same thing happened in a brush-tailed bettong reintroduction, with the radio collars of 14 animals—a fifth of the total—giving out the “dead” signal one by one over a period of four months. Eliminating a single 12.6-pound cat ended the problem.
For their study, Moseby and her colleagues looked at an attempt to reintroduce 41 western quolls—a predatory marsupial once common throughout Australia—into Flinders Ranges National Park. They retrieved the 11 animals that died and, among other forensic techniques, took swabs of the saliva on the radio collar and on the carcass for matching with samples from captured cats. In one typical case, a professional shooter killed a large male cat near a quoll kill site, and not only was its DNA identical to that found on the dead quoll, but its teeth matched the bite marks on the victim, and it had quoll fur in its stomach.
The problem for challenging species reintroductions, said Moseby in an interview, is that certain cats—generally large males—learn to deal with the challenges and then specialize in that prey, coming back again and again. Ducks aren’t exactly challenging, but swimming usually is for cats. Yet in one notorious case, a cat was shot while swimming out to gray teal nests—and it had gray teal in its stomach. It was a serial killer. Moseby likened the proposed response to the way society generally deals with other “problem predators”: The conventional practice is not to eliminate all tigers or polar bears, say, but to target only individuals that have become a menace to humans.
In the case of cats, attempting to eradicate the entire free-roaming population isn’t generally practical, except on small islands. It can be more efficient, said Moseby, to identify and eliminate just the problem felines. Or, because DNA and other forensic techniques are still relatively expensive, it may require eliminating the type of cats, those large males that are prone to causing problems for challenging prey. That can mean setting large box traps or using auditory signals to target those cats. “We’re trying to show that not all cats are created equal,” said Moseby. “Only a proportion of the animals are doing the damage.”
But aren’t some cat owners going to interpret that to mean their cat is innocent and should be free to roam outdoors? “I can see that there’s a potential for that,” she acknowledged. “But we’re only talking about challenging species—prey species that are larger, more aggressive, and have defensive mechanisms. Whereas for things like native lizards or native mice, they might be vulnerable to any cat.” That’s why Australia recently launched a “war on cats,” with a plan to cull 2 million feral cats over the next five years. Environment Minister Greg Hunt described the program as an attempt to “halt and reverse the threats to our magnificent endemic species.” (In New Zealand, where cats have also devastated endemic species, an economist and an environmentalist have proposed a ban on all domestic cats.)
But cats are unlikely to go away anytime soon. So Moseby is working on one initiative to make native species more cat-savvy. Researchers now have 450 burrowing bettongs, small marsupials, in a nine-square-mile fenced paddock with two cats. The aim is to fast-track evolution and over a few generations breed up populations that can survive even with cats in the area. “We don’t want to be building fences forever and excluding these animals completely,” she said. That just encourages prey animals to become more naive about predators.
Another more radical initiative in the works at the University of Adelaide would automatically target and kill problem cats at the scene of the crime: Researchers are developing “toxic microchips,” said Moseby, that could turn a prey animal into “a toxic Trojan horse.” The chip, implanted in an animal’s skin, would not harm the carrier. It uses a local toxin to which indigenous species have adapted but introduced species haven’t. The chip is designed to break open during the shredding and rending of a predator attack and thus poison the killer—specifically a cat or another introduced species. That may sound like cruel and unusual punishment to cat lovers. But if their cats are really as innocent as they like to say, they won't encounter the problem in the first place.
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