In recent years, many cat-lovers have participated in a growing trend of letting their domestic cats "do what's natural," allowing them outdoors to play and wander like their wild counterparts -- which isn't actually natural at all. Cats are technically an invasive species, and they've been shown to kill more than one billion birds in the United States each year. As Richard Conniff writes in the New York Times, outdoor cats are contributing hugely to a "second Silent Spring" that's putting the world's wildlife at risk:
The National Audubon Society tracks 20 common North American bird species - Eastern meadowlarks, field sparrows and the like - that are now in decline. Their numbers have dropped by 68 percent on average since 1967, because of a variety of factors. In Britain, likewise, farmland bird populations have plummeted just since 1995, with turtle doves, for instance, down by 85 percent, cuckoos by 50 percent, and lapwings by 41 percent.
According to Conniff, the growing population of household cats (84 million and counting) combined with an estimated 30 to 80 million stray cats is causing the incremental destruction of many species -- not just birds:
Using deliberately conservative assumptions, federal researchers recently estimated that free-ranging cats killed about 2.4 billion birds annually in the Lower 48 states, a substantial bite out of the total bird population. Outdoor cats also kill about 12.3 billion small mammals a year - not just the proverbial rats and mice but also chipmunks, rabbits and squirrels - and about 650 million reptiles and amphibians. In some cases, they are pushing endangered species toward extinction.
But here is the number that sticks in my mind: Letting my own cat, Lucky, outdoors may have consigned as many as 33 birds and dozens of mammals to death every year. If you have ever seen a cat toy with its victim, you know these are not quick, or pretty, or painless deaths. So you might expect animal welfare groups to be ardently campaigning against outdoor cats, and particularly against the care and feeding of feral or stray cats, which do most of the killing.
Many animal welfare groups and shelters, however, rely on T.N.R. (trap-neuter-release) policies to keep feral cat populations down, which Conniff argues do little to control stray felines' numbers. Although T.N.R. can bring down euthanasia rates, it might not be the most effective strategy for making the great outdoors safer for cats, or for the humans the interact with them.
Instead, Conniff advocates keeping all felines indoors, which he predicts many cat-owners will begin to take seriously as the rates of death and disease become increasingly frightening for animals and the humans who love them. "Cats are three to four times more likely than dogs to carry rabies, according to the Centers for Disease Control and Prevention," he writes. "They also share many other parasites or infectious microbes with humans, including roundworms, hookworms, giardia and campylobacter. When cats live outdoors it is almost impossible to predict what they will bring home next." And that, Conniff says, is reason enough to keep them home in the first place.