Our environment is facing a crisis. No, I’m not talking about the runaway carbon emissions that are ruining our climate. Rather, I’m talking about a threat that lives inside of our very own homes: the domestic house cat. 

For all of their cuddly cuteness, when left to roam the outdoors on their own, domestic cats are the number one threat to birds and small mammals. As soon as they get a taste of fresh air, they transform into vicious predators, reigning terror over the local habitat. By one estimate, domestic cats kill 1.4–3.7 billion birds and 6.9–20.7 billion mammals every year. That’s more birds than have been lost to habitat loss and pesticides in the last 40 years. 

According to the authors of the study these numbers come from, free-ranging domestic cats are the “single greatest source of anthropogenic mortality for U.S. birds and mammals.” The International Union for Conservation of Nature listed domestic cats as one of the world’s 100 worst invasive species

In other words, Sprinkles McFluffington and her buddies are a disaster for the planet.

How did we get here?
The Near Eastern Wildcat

Archaeologists estimate that cats, as we know them today, find their origins in the middle east and northern Africa. They believe people started domesticating the near eastern wildcat about 12,000 years ago. The domestic cat initially served as a religious symbol, but later, we found how useful they could be in controlling pests. As humans transitioned from hunters to farmers and began the practice of storing surplus grain, cats kept pests, such as mice, away from their food.

But then, people started distributing cats all around the world. And that’s when the trouble started.

When people introduce a non-native species to a new region, it disrupts the natural environment, throwing off the delicate balance between predator and prey that has been established over eons. Invasive species eat the prey of native predators, leaving them with nothing to eat. That prey is also predator to smaller things, such as insects and plants, and without anything to feed on them, they overgrow. Since cats are not native to the United States, ,they become the apex predator outdoors, killing all the small animals they can find. By all accounts, the domestic cat is an invasive species.

The Size of the Problem

Americans own an estimated 85.8 million cats, and about two out of every five cats are allowed to roam outside. A survey of veterinarians tells us that people let their cats outside to provide them a more “natural” environment. Cat owners see their cats crying at the door and escaping outside as signs that the cat would be happier outdoors. This makes intuitive sense – animals, after all, do belong outside. But as I mentioned before, animals don’t belong in their non-native habitat.

Indoor/outdoor cats are only part of the problem. We can attribute the majority of cat-caused environmental destruction to feral cats — cats that were born outside and aren’t owned by anyone. By some estimates, there are more feral cats than house cats, perhaps up to 160 million. Of all cat-caused animal deaths in the United States, feral cats account for about 70% of bird deaths and 90% of mammal deaths.

Wherever in the world you find people, you’ll find feral cats. Their impact is especially troubling on islands, the home of Earth’s greatest source of biodiversity. Researchers have found that feral cats are responsible for the extinction of 14% of all mammal, bird, and reptile species on islands, and they are the primary threat to 8% of those that are left.

You may have heard of groups starting trap-neuter-release (TNR) programs in your neighborhood as a humane solution to the feral cat problem. This process involves grabbing feral cats off the street, neutering them so they can’t have kittens, and putting them back outside. The goal is to reduce the feral cat population. But, unfortunately, there is no evidence that these traditional TNR programs actually work. 

Part of the problem is that TNR proponents are seeking the wrong solution. They often discuss a program’s success based on the welfare of the animals, and not on the health of the environment. For example, some programs aim to reduce accidental cat deaths, decrease euthanizations, and reduce the economic cost of feral cat colonies. In the meantime, feral populations have not budged. In reality, at least 3 out of 4 feral cats need to be neutered for the population to decrease, and there’s no evidence that any communities have been able to obtain that level of TNR. 

Fortunately, researchers are developing better TNR methods that show signs of success in reducing feral cat populations. But it takes years to see if a new method is working and to get the word out so it gets adopted across the country. So, we cannot simply rely on others so solve the problem.

How Can You Help?

While scientists and activists work to reduce the feral cat population, there’s one simple trick to keeping your own cat from harming the wildlife in your backyard: keep your cat inside! If the thought of keeping your cat in your dark, musty apartment doesn’t work for you, you have other options. Here are some tips on how to give your cat some fresh air without letting them pose a threat to other animals:

  • Get a cat leash and “walk” your cat without letting them roam free.
  • Build a “catio,” or an enclosed space outside where your cat can get some fresh air and some exercise.
  • Open your windows (but leave the screen shut), so your cat can take in some sun and air but not any birds and mice. 

If cat walks and catios are not an option, there are still ways you can enrich your cat’s life and give them some exercise indoors:

  • Give them toys. They don’t need anything elaborate – a string on a stick, a clothespin, or a hairpin might be enough for them.
  • Get a laser pointer. Many cats love chasing the dot. Get them running after it.

If you want to make a difference in your community, start talking about this problem with people who can make a difference. Most cat owners don’t realize the harm that their sweet little pet can bring to the environment. But with some awareness, your fellow cat owners will learn the importance of keeping their cats inside, and like you, they will become advocates for change. Furthermore, with the right pressure, policymakers can start taking action to reduce the feral cat population through research and the adoption of more effective TNR programs.

Keep one cute animal indoors, and save so many more.


  • Ben Marcus

    Ben Marcus is a public relations specialist at CG Life and a co-editor-in-chief of Science Unsealed. He received his Ph.D. in neuroscience from the University of Chicago.

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