In a recently published study, my Smithsonian colleagues and I demonstrated that cats are the primary predators of young catbirds soon after they leave the nest. In fact, in some areas, less than 15 percent of these fledglings survived, largely because of cat predation. Free-ranging cats have turned the D.C. suburbs into ecological traps for birds — sites that attract them for nesting but ultimately cause high levels of reproductive failure.
The free-ranging domestic cat, both pet and feral, has become by far the most abundant mammalian predator on Earth, numbering 80 million to 120 million in the United States alone. You need only look into a neighbor’s yard or down an alley to find one. Unlike our native bobcat and lynx, free-ranging cats are as invasive and disruptive to native ecosystems as gypsy moths or West Nile virus.
Whether they are pets allowed to roam, fully feral animals or feral members of a trap-neuter-release (TNR) colony, domestic cats are by nature predators of small animals such as reptiles, birds and mammals — even when they are well fed. It’s not surprising, then, that they have been responsible for numerous animal extinctions on islands. The millions of free-ranging cats in the United States are inflicting similar devastation on wildlife populations here.
I don’t enter lightly into the long-standing debate about free-ranging cats. On one side are people who think cats have a right to roam freely; on the other are those who believe a cat’s only proper place is inside a home. I come down with the latter because, apart from their impact on wildlife, outdoor lifestyles ironically also have negative consequences for cats. The American Veterinary Medical Association estimates that free-ranging cats have half the life expectancy of indoor cats. Causes of cat death can be gruesome — getting hit by cars, being mauled by dogs or becoming a meal for foxes and coyotes. Life outdoors also means greater exposure to diseases such as toxoplasmosis and feline leukemia. Cats are now the most common domesticated animal to carry and transmit rabies to humans and other wildlife.
The most egregious example occurs with feral cats living in or near TNR colonies. Maintenance of such colonies remains common in many urban and suburban parks and even some national wildlife refuges. The cats in these colonies, although fed, not only suffer the same fates as those described above for free-ranging ferals but the places in which they live can become devoid of most wildlife. Worse, these colonies encourage the dumping of unwanted cats. While neutering can slow a colony’s growth, it is rarely fully effective because more than 70 percent of the cats must be sterilized. New cats arrive, and many go unneutered and unvaccinated. The result is reproductively active colonies that continue to devastate wildlife.