cat killer_2015_02_09
The restaurant menu of species consumed by Australia's feral cats is exhaustive. In all, researchers have found evidence for predation on 400 different vertebrates. Image: sunphlo, Flickr

The feral cat is a relentless predator, lurking in the shadows behind every tree and beneath every bush, just waiting for an unsuspecting bird or small mammal to wander by ... and then SNAP! the domestic-cat-turned-wild has caught it between its teeth, the poor animal destined to become yet another statistic.

According to a 2013 study in the journal Nature Communications, outdoor cats – both pets and street cats – in the United States gobble up between 1.4 and 3.7 billion birds each year. And another 6.9 billion to 20.7 billion small mammals. 

Clearly, it's not as if our feral cat problem will be solved by not leaving pet food unattended in our backyards (that will certainly help with plenty of other problems, though). "Reducing the impacts of feral cats is a priority for conservation managers across the globe and success in achieving this aim requires a detailed understanding of the species’ ecology," argues researcher Tim S. Doherty of Australia's Edith Cowan University.

So Doherty and his colleagues rounded up data on what feral cats were eating in Australia and its nearby islands, and they compared that to geographic location, temperature, rainfall and other environmental factors. They published their findings online this week in the Journal of Biogeography.

Understanding the ecology of feral cats is key not just because they are such a nuisance; it's because they're a major threat to Australia's native wildlife. They're considered a "contributing factor" to declines in Australia's mammals and are classified as a "key threatening process" under the Environment Protection and Biodiversity Conservation Act.

The laundry list of species consumed by Australia's feral cats is exhaustive. In all, the researchers found evidence for predation on 400 different vertebrates including 123 birds, 58 marsupials, 57 reptiles, 27 rodents, 21 frogs, five bats and nine exotic mammals. Of those, a whopping 28 species are listed as threatened by the IUCN: three critically endangered species, five endangered, eight vulnerable and 12 near threatened. That's in addition to the multitude of invertebrates that found their way into a cat's digestive system, including insects from 13 different orders, plus spiders, scorpions, centipedes and crustaceans. It seems as if the only animals not on the menu were those physically too large to fit in the cats' jaws.

But the important finding? Although rabbits are the staple prey of feral cats throughout Australia, the feline predators will feast more often on rodents and small rodent-sized marsupials (called dasyurids) in areas where their choice prey can't be found. To a feral cat, a rabbit may be like a pricey filet mignon, but the cats are scrappy: if there's no rabbit around, they can easily switch to other sources of nutrition. 

Rabbits, like feral cats, are invasive in Australia. They were initially brought there as food, but as is so often the case, the rabbits eventually escaped or were let loose for sport hunting, eventually colonising the entire continent. Like the cats, the rabbits have made severe impacts on Australia's native ecosystems. Native plants are like a salad bar for them. Overconsumption doesn't just impact vegetation, but also geology. By eating up so many plants, the rabbits have caused widespread erosion. They also help themselves to crops, making them particularly unwelcome on agricultural farmlands.

What this means is that control programs aimed at culling rabbits may have the unintended consequence of increasing the likelihood of feral cat predation on other small native mammals. Of course, the answer to the feral cat problem is not to introduce more rabbits. Nor is more cats a suitable solution to the rabbit dilemma. 

"The interplay between cat diet and prey species diversity and abundance at a continental scale is complex," the researchers conclude. There is probably no good answer to the compounded problems of feral cats and invasive rabbits in Australia. Instead, the researchers suggest, conservation managers are probably limited to working at the "local landscape level." Which probably means trying to keep both rabbits and cats as far away as possible.

Top header image: Chriss Haight Pagani, Flickr

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