The ASPCA estimates that 74 million to 96 million cats are owned in the United States, making them the country’s most popular pet. While many of these cats are kept indoors, others are allowed to come and go as they please or even roam outside full-time — an allowance that’s become a growing source of controversy in recent years.

What’s all the feline fuss about?

A 2012 study by the University of Georgia and National Geographic found that U.S. cats could kill as many as 4 billion birds and small mammals a year, and in 2013, similar research by the Smithsonian’s Migratory Bird Center and the U.S. Fish and Wildlife Service concluded the real numbers were even higher.

The majority of these animal deaths were attributed to feral cats or stray cats, but the 2013 study notes that domestic cats allowed to roam outdoors “still cause substantial wildlife mortality.”

Conservation groups like the National Audubon Society encourage cat owners to keep their pets indoors for the protection of wildlife. And animal welfare agencies, including the Humane Society and the American Veterinary Medical Association, have echoed this sentiment, pointing out that indoor cats also live substantially longer than outdoor ones because they’re not exposed to traffic, disease and other animals.

However, many cat owners — including animal experts — continue to let their pets outside despite these risks, and they have convincing arguments of their own.

For one, domestic cats remain genetically quite similar to their ancestors, meaning they still have many of their wild instincts.“ Unlike our canine companions, our felines have retained their wild streak. To see a cat outside is to see a creature in its element,” David Grimm, author of “Citizen Canine: Our Evolving Relationship with Cats and Dogs,” told The Washington Post. “You could keep your cat indoors and give him a comfortable, safe life. You could also keep your race car in a garage.”

In addition to this, there’s a wealth of evidence that an indoor-only life can actually be unhealthy for some cats. Felines that spend nine lives inside can suffer from health issues like obesity and diabetes, and they also may display boredom-related behavioral problems such as aggression and eliminating outside the litter box.

When it comes to whether or not to allow cats outside, animal writer Hal Herzog says he’s “more morally conflicted about [it] than any other animal issue,” but ultimately, it’s up to each cat owner to decide what’s best for their pet.

Luckily, there are numerous ways you can keep your cat physically active and mentally stimulated — both indoors and out — while still protecting the local wildlife.

Venture outside safely

white cat walking outside on a leash You can let your cat explore safely outdoors while walking on a leash. (Photo: denrz/Shutterstock)

If your kitty craves outdoor time, let him outside under supervision. Many cats can adjust to wearing a harness and walking on a leash — some simply require more training than others. Not all cats will want to go on a walk like a dog; however, they may enjoy exploring the backyard, nibbling on grass and soaking in the sun.

“Just like a dog, a cat can be attached to a long line when in a fenced back yard or other space,” said veterinarian Jennifer Stokes, a professor at the University of Tennessee’s College of Veterinary Medicine who walks her cat Simon on a leash. “But they should be monitored closely at all times to be sure they do not get caught or tangled on a structure.”

Another safe way to allow your cat to enjoy the great outdoors is by giving him access to a screened-in porch or another enclosed outdoor space like a catio. “Simon and my other cats have access to enjoy their screen porch and cat enclosure at all times,” Stokes said.

If you decide to take your feline friend outdoors, make sure he’s microchipped and wearing a collar with identification tags. Also, be sure your cat is up to date on flea, tick, heartworm and intestinal parasite preventatives.

Make the indoors more stimulating

gray kitten playing inside Keep indoor kitties happy with lots of playtime. (Photo: casey christopher/Shutterstock)

While the natural world offers kitties endless opportunities for exercise and entertainment, your cat doesn’t necessarily have to go outside to enjoy them. There are many ways you can give your cat stimulation similar to what nature provides.

Enrich your cat’s environment. Felines need space to climb, scratch and hide, so outfit your home with kitty furniture, cardboard boxes and scratching posts. Vertical space is especially important to cats, so consider purchasing or building a cat tree. “Providing vertical space increases the relative size of a cat’s environment, as well as helps to meet its instinctual need for safe space off the ground,” Stokes said.

You can further enrich your cat’s living space by setting up some “Cat TV.” Place a bird feeder or birdbath within view of a window, and, if you have narrow window sills, consider installing an indoor window perch, so your cat can sunbathe and enjoy the view.

Play with your cat. Playtime is important for your cat because it allows him to engage in natural behaviors like hunting and pouncing. “Nothing is more stimulating or bonding for cats and their owners than interactive play,” said holistic cat behaviorist and celebrity cat consultant Layla Morgan.

Keep in mind that when you’re engaging your cat in play, how you play is just as important as the toys you use.

Introduce a puzzle feeder. Studies show that felines are happier and healthier when they have to work for their meals, so consider feeding your cat from a food puzzle, a device that releases kibble when a cat interacts with it.

Mix it up. Just as children can get bored playing with the same toys, so can cats. Rotate your cat’s toys from time to time, putting some out of sight and reintroducing old favorites. Also, change up your play sessions and try out new games from time to time.

“The biggest issue I see is complacency and boredom,” said Morgan. “Life is constantly in flux. The perch next to the window may have worked six months ago for bird TV, but might be boring now. Mix it up. Move it to a new location, or add a new interactive toy. Introduce new sights, sounds and natural smells regularly. It can be spontaneous like coming home from the grocery store and placing a treat inside a paper bag or a planned weekly kitty fun date with homemade toys.”