Cats – and, by extension, their keepers – have major effects on the wellbeing of other animals. As with other domestic carnivores, cat keepers can generally reduce suffering by avoiding overfeeding, and by choosing cat food made from larger animals, fewer of whom are killed to produce comparable amounts of products in those industries. However, far more important is to eliminate painful animal deaths and injuries that result from letting cats outdoors. Cat keepers can prevent a large amount of serious and avoidable suffering by keeping cats in their homes. The purpose of this article is to share a detailed look at the cost of letting cats out, and to convince cat keepers that in general keeping cats inside is the right thing to do. It also suggests some steps cat keepers can take to reduce the harms of letting cats out, and ways to reduce dissatisfaction cats may experience from not going out.

In general, people who let their cats out do so because they recognize that their cats want to go out. This motivation reflects an intention to do well by animals – to imagine what they experience, to empathize with them, and to act in their interests as best we can. However, it extends this consideration only to some animals, neglecting the large number of others whose lives are affected by this choice. Most cats attack other animals whether or not they need to eat them. Moreover, the particular hunting behaviors of cats frequently result in drawn-out killings that involve long periods of fear and pain. Cats often claw animals until they apparently die from shock or heart attacks, rather than from direct wounds or blood loss, which quicken lethal encounters with many other kinds of predators.

Outdoor cats cause these kinds of deaths on a huge scale. According to the first large-scale study of its kind, outdoor cats are likely the single greatest source of human-caused wild mammal and bird deaths in the U.S. This means more mammals and birds in the country are killed by cats than by accidents involving planes, cars, and other vehicles, or by collisions with buildings, wind turbines, and other human structures, or by intentional and unintentional human-caused poisoning of all kinds, or by every kind of construction and development activity. Using fairly conservative methods, the authors concluded that in a single year, cats kill 2.4 billion birds and 12.3 billion mammals, amounting to a total of 14.7 billion (14,700,000,000) animals. This is 5.5 billion more than the number of farmed mammals and birds slaughtered in the country in 2015 (the most recent year for which a complete count is available) according to the USDA. And it completely neglects cat killings of reptiles and amphibians, which likely number in the hundreds of millions annually.

When people discuss this tremendous loss of life, they usually frame it as an environmental issue. But it is also a serious animal welfare issue. As I’ve emphasized, cats are often inexpedient killers who mutilate animals over prolonged periods of time. You can attest to this fact if you have ever received a “half-dead” animal from your cat. Importantly, we can acknowledge the exceptional suffering involved in these killings without vilifying cats at all, since there is no evidence that they have a theory of mind encompassing the subjective wellbeing of any of the animals they commonly kill. But however we wish to qualify it, a balanced perspective must acknowledge that the suffering cats inflict in their attacks makes their presence outside a serious detriment to outdoor animals’ wellbeing. When we choose to let cats out, we choose to affect other animals in this way.

This choice is being made on a scale with a high cost in suffering, and there are clear reasons not to make it. Most people do not let their cats out when they know other animals outside might kill or maim them. For example, coyotes frequently attack and kill cats where I live in Massachusetts, and many people try to keep their cats indoors during the times that coyotes are most active. Clearly, the implication of such choices is that letting a cat outdoors is not worth the risk of that cat being severely hurt or killed. But when no such predators threaten cats, regularly letting a cat out actually results in a larger number of animals being as severely hurt or killed – and typically in a more painful and frightening way, since predators that kill cats almost always kill them in quicker and more direct ways than cats kill other animals. With this fact in mind, letting a cat out only makes sense if we believe the cat’s experiences are much, much more important than the experiences of these other animals. And since the pain capacities of cats are very similar to the pain capacities of other mammals as well as birds, this belief is clearly unwarranted.

The best move for all animals is to simply keep cats indoors. This is true even if they find it dissatisfying, since the dissatisfaction they experience is not worse than the prolonged fear and pain of being maimed or killed (and certainly not worse many times over – the appropriate consideration since individual cats attack many animals outdoors). Fortunately, cats who are provided with adequate stimulation indoors do not seem to experience such dissatisfaction. Yanking around soft toys on strings is a good way to provide cats with exercise and outlets for their hunting behavior. You can buy toys or make them – a string tied to any safe, soft object with enough weight to bounce around works fine. (Just make sure to keep toys with string or similar parts inaccessible when you’re not using them so cats can’t eat them.) You can also buy scented toys that your cat might like to chew on. Or, again, you can make them by spraying nontoxic scents onto toys you already have. If you don’t have a lot of time to play with your cat, you can also ask any available friends or family for help, or make it a chore required of kids in your house. These are also opportunities to spread awareness of wild animal suffering in your community.

Finally, there are a number of ways to reduce the likelihood that cats will harm animals if let out, although none comes close to full prevention. The most important thing is to be absolutely sure they are spayed or neutered. A large population of feral cats is a major contributor to wild animal deaths as well as suffering by cats, since strays face many kinds of diseases, parasites, and injuries from vehicles and infrastructure, as well as scarcities of food, water, and shelter. One method for directly preventing attacks is to use reflective and/or brightly colored collars that visually alert animals. However, these collars do not effectively alert many animals – including most mammals, who do not have especially vivid color vision. It is worthwhile to note that while most amphibians, reptiles, and birds see the same colors as humans (and many see more), most mammals other than apes do not see reds, so only collars with flashy blues and yellows stand even an outside chance of alerting them. Another method is to attach a bell to your cat’s collar. But cats learn to adapt their movements to keep bells quiet, and not all animals can hear them in the first place. You can increase this method’s effectiveness by using multiple bells, or by changing the bell regularly. If you will not keep your cat indoors, I encourage you to use both of these methods. But ultimately neither is sure to protect animals from consequences that you likely would not risk for your cat by letting him or her out.