It is a true New York Times story that involves issues of conservation substance. In Texas, a Jim Stevenson shot a feral cat that was attacking an endangered bird species – the Piping plover. Feral cats are among the most destructive animals in the natural environment. Stevenson was put on trial with some competing groups baying for blood (the cat lovers see it as ‘natural’ for cats to kill birds) and others seeing him as a heroic defender of the natural environment. Finally, the jury reflected the complex mix of moral issues here and could not agree on a verdict - he was acquitted.
I don't dislike cats on an individual level and recognise the great pleasure they bring people. Generally I am interested in pets that live with humans. Recent economic theory extends models of the household to include pets – which are treated as complementary or substitute inputs into the services provided by households. In Australia we spend huge amounts on pets. We have about 2.4 million domestic cats and far more than that are feral – unlike children people routinely buy and then dump pets that are unwanted.
Some identify positive benefits on people from owning pets are claimed to arise in the form of biophilia or ‘biological fitness’ benefits from an association with non-human life. Of course one can enjoy nature and non-human life without keeping pets.
But I do have specific problems with cats that are not constrained, by being kept inside a house or on a leash, from killing native wildlife. I recognise that restraining them limits their welfare and perhaps that of their owners but because I place weight on the natural environment I can live with that. The positive benefits that can be gained from having pets can then be gained without imposing negative external costs on the environment.
(Parenthetically I also have problems with dogs inside a house – the pervasive doggy smell that runs through carpets and furnishings puts me off.)
It is however very difficult to rid the environment of feral cats and indeed foxes. In fact shooting them is not very effective since – like foxes – they bread prolifically. A few crushed aspirin tablets mixed with tuna fish will kill unwanted cats in bushland or your backyard but, of course, approach any known owners with concerns, before you employ such solutions.
There is some limited work on the biodiversity effects on cats in Australia. A longer report is here. Everyday observation confirms that they are, in close competition with foxes, one of our most destructive environmental forces. This motivates my preference for trying to introduce nature as a part of our urban environments and to enjoy this rather than to keep environmentally destructive pets that cost society so much in private costs and external costs to the environment.