"Killer" Cats?

The past fifteen years have witnessed a rising tide of invective directed by conservationists against cat owners. However, hard evidence connecting pet cats – as distinct from unowned aka “feral” cats – with long-term damage to wildlife populations has been hard to come by. Unowned cats are a different story: they have undoubtedly caused extinctions on oceanic islands, and a recent review by the Smithsonian Institute of data from the United States came to the conclusion that unowned cats are responsible for far more bird and small mammal mortality than pet cats are. In Australia, where cats are an introduced predator and might reasonably be expected to have a disproportionate impact on local wildlife, restrictions imposed on ownership of cats or restricting their outdoor access have not resulted in surges in the numbers of their common prey species.

Although many pet cats do not hunt at all, or with only minimal success, estimation of the numbers that they do kill (usually based upon their owners’ records of prey brought back to the home) can produce superficially alarming numbers. For example, the Smithsonian study indicated somewhere between 500 million and a billion small birds each year in the USA alone. At first sight it is difficult to square such figures with the observation that not only are the animals brought home by cats not necessarily in decline, but some are actually thriving: in the UK, blue tits (chickadees) are among the commonest birds that cats bring home as corpses, yet over the past quarter-century their numbers in British gardens have increased by about a quarter.

There are several possible factors that may ameliorate the potential impact of pet cats on the populations of their prey. One is that pet cats, being largely well-fed, are not hunting “seriously”, and so only have the skill and/or the motivation to kill animals that are already weakened by other factors. Indeed, this was the conclusion of a study conducted in Bristol, UK; that predation by pet cats, in ecological language, “represents a compensatory rather than additive form of mortality”, i.e. making no difference to next year’s populations. Another is that urban birds seem rather adept at avoiding getting caught, somehow more so than their rural cousins who presumably have a wider range of predators to worry about. A third is that even pet cats are not the only predators involved, and, by preying on animals such as rats that themselves eat birds’ eggs and the young of both birds and mammals, may actually have a positive impact on wildlife numbers in some areas. Indeed, this may be the case in New Zealand, where (also introduced) rats are rated as the most serious pest (cats – including ferals – come in a distant fifth). It must also not be forgotten that in the USA, cats are the victims of predation well as perpetrators: in some areas, cats form about 10% of the diet of coyotes, and fear of coyotes seems to restrict their ranges, especially at night.

Evidently, the ecology of predation by pet cats is more complex than a simple one-to-one relationship between deaths and wildlife populations, yet this does not seem to deter conservationists from scapegoating owners of pet cats. In the USA, the risk that coyotes pose to cats has been posited as a useful weapon in urban wildlife managers’ campaigns to have all cats restricted indoors. A recent study conducted in villages in Cornwall, England, and in Scotland has examined cat owners’ attitudes to their cats’ predatory habits: the authors concluded that ‘Cat owners failed to perceive the magnitude of their cats’ impacts on wildlife and were not influenced by ecological information. Management options for the mitigation of cat predation appear unlikely to work if they focus on “predation awareness” campaigns or restrictions of cat freedom.’ However, since ecologists have failed to produce concrete evidence that pet cats actually affect wildlife populations year-on-year in the UK – even the Royal Society for the Protection of Birds blames habitat destruction – perhaps cat owners’ resistance to such strident calls for their re-education is not only justifiable, but perfectly logical.