It is widely accepted that indoor cats tend to live longer and healthier lives than cats allowed to roam outside. An indoor cat will likely never get hit by a car or attacked by a marauding domestic dog or coyote. They will not contract the retroviruses that are common in feral cat populations, nor be affected by the various other parasites and infections to which outdoor cats are susceptible. Cats do not necessarily need to be let outside to live happy and fulfilling lives as long as appropriate environmental enrichment is provided to maintain their mental and physical well-being; I have owned and known many indoor cats that were content watching the world around them from a cozy windowsill or lounging on a screened porch. Plus, keeping cats indoors has benefits beyond enhancing well-being—native wildlife also benefits when cats are kept indoors.
Humans have introduced domestic cats around the world, at times with dire consequences to native wildlife, especially on islands. Free-ranging cats introduced to islands are estimated to be responsible for ~15% of documented extinctions of island birds, mammals, and reptiles, and are the major threat to many imperiled species of island fauna1. Additionally, feral cats are believed to have played a significant role, along with other introduced species, in the decline and extinction of numerous mammals in Australia.
Cats do not necessarily need to be let outside to live happy and fulfilling lives as long as appropriate environmental enrichment is provided to maintain their mental and physical well-being.
The number of native birds, mammals, and other vertebrates killed by outdoor cats in the U.S. each year is staggering, and enough reason for cat owners to keep their pets inside. Studies conducted by Smithsonian Conservation Biology Institute scientists estimated that outdoor cats (owned and feral) kill 1.3 to 4 billion birds and 6.3 to 22.3 billion mammals each year,2 most of which are native species as opposed to introduced vermin (eg, house mice, black rats), although this varies across habitat type. Additionally, the scientists estimated that several million reptiles and amphibians also fall prey to outdoor cats each year in the U.S. They concluded that free-ranging cats are likely the “single greatest source of anthropogenic mortality for U.S. birds and mammals.”
Outdoor cat owners often are under the false assumption that collar-mounted warning devices (eg, bells, sonic devices) will prevent their cats from killing wildlife, and some studies have shown that these devices can reduce the number of animals killed by cats.3,4 Nonetheless, cats outfitted with such devices still kill many wild animals, and cats may learn to adapt their hunting skills over time,3 reducing the effectiveness of the devices. In addition, because reptiles rely largely on visual, chemical, and temperature cues to sense their environment, auditory cues likely provide little warning that a cat is ready to pounce. Fledgling birds and baby mammals are unable to escape a predatory cat even when they are aware of the cat’s presence.
A second misconception is that fed cats don’t kill wildlife. Hunting is an inherent instinct in the feline family tree—cats (domestic and wild) are highly evolved predators. A controlled experiment conducted in the 1970s showed that domestic cats would cease eating a preferred food to attack and kill a live rat.5 After killing the rats, the cats took them back to their food dish and resumed eating their preferred food. In another study, 3 free-range, daily fed house cats killed an average of 750 small mammals annually over a 3-year period.6
Outdoor domestic cats—both hungry feral or well-fed owned felines—are prolific hunters and kill billions of native birds and mammals each year in the US. Here and abroad, domestic cats have contributed to the decline of many terrestrial vertebrates, and have even caused the extinction of species once endemic to oceanic islands.7 These devastating ecological effects far outweigh any potential benefits for allowing cats to range outdoors. Veterinarians need to take a strong and unwavering stance with their clients and insist they keep their cats inside.