Feral Cats & Wildlife

The Australian hatred of cats, especially ferals is well known. The idea that feral cats are responsible for the decimation of indigenous wildlife underlies this sentiment. However a recent article in The Sydney Morning Herald, August 29, 2013 sheds new light on this controversial issue:

According to the article by Gabriel Popkin, titled, Feral cats help some endangered mammals survive, foxes and feral cats, who are both very unpopular among conservationists are basically misunderstood. These two animal species are infamous for killing off the Australia’s native species, and have been the targets of numerous government-backed eradication campaigns. The article argues that new research suggests that on islands, these predators help control an even more destructive one: the black rat. As a result, eliminating cats and foxes could actually leave native mammals more vulnerable to predation, competition, and ultimately extinction.

In order to plan successful eradication campaigns, scientists must first understand how introduced predators interact with native fauna and with each other. For instance, cats and foxes are infamous for hunting birds and other wildlife, but they can also control rats, which are themselves ferocious killers of and competitors with native animals like the bandicoot. To date, few studies have looked at which type of predator is actually most likely to drive native animals extinct.

To determine which island invaders were doing the most damage, scientists created and analysed a large database comprising 934 living and extinct populations of 107 mammal species on 323 Australian islands between the early 1800s and today. For each island, the researchers recorded the presence or absence of various native mammals, and of rats, cats, foxes, and dingoes, which some scientists believe help control invasive predators. The researchers also included other factors that might affect extinction risk, such as the size of the island and distance from the mainland. (Ecologists have found that island populations close to continents are more easily replenished, while more distant populations more easily go extinct.) Researchers then analysed the data to find which factors most often correlated with native mammal extinctions.

The study yielded some surprising results: Native mammals were most likely to die off on islands that had rats, but not cats, foxes or dingoes. Extinction rates on such islands ranged from 15 per cent to 30 per cent, but when cats, foxes or dingoes were present, the rates plummeted to just over 10 per cent – not much higher than on islands without any introduced predators, the scientists reported in the journal Global Ecology and Biogeography.

The scientists also found that native mammals fared only slightly worse on islands with cats than on islands without them. Moreover, the presence of foxes and dingoes on islands seemed to give native species a slight overall boost.

Despite the apparent benefit of cats and foxes, conservationists do not advocate introducing the animals to islands that don’t already have them. Importantly, this study raises raise questions about the strategy of trying to kill top predators off while ignoring rats.