Recently, on Reddit, I was called “a bad person. Bad.” Why? Because I asked those in my neighborhood to stop putting out bowls and bowls of cat food in public parking lots for feral cats. (Cat food, by the way, is dangerous for deer and many other animals, and it attracts rodents.) Others, who didn’t resort to name-calling, said it was cruel to let these favored—because that is what we are talking about here—animals starve.

I like cats—I grew up with them and they are marvelously self-contained. But you know what I like better than cats? Our ecosystem. And outdoor cats are ruinous for our world.

Apart from habitat degradation—caused by agriculture, deforestation, and urban growth—cats are the single largest killer of birds. Most scientists estimate that cats in North America kill two and a half billion birds a year. (The annual net population loss is, conservatively, sixty million birds.) Feral cats are the largest contributor here—they account for almost 70% of all cat-caused bird deaths. Each feral cat kills thirty to forty birds a year.

So if you feed a feral cat, you are deciding—whether consciously or not—that one cat is worth more than thirty to forty birds.

This, if you ask me, is nuts. (And, again, I like cats.)

Since 1970, North America’s bird population has declined by 30%. That adds up to almost three billion missing birds. Without birds, our planet and its people are unlikely to survive. Without birds, insect and rodent populations will explode. Diseases will multiply. Forests and plants will disappear. Our food chain will break down. Our world without birds will ultimately become uninhabitable.

Bad person or not, I’m willing to let feral cats starve and to hector others to keep their pet cats indoors at all times. That may be hard on cats, but it is long past time we stopped being harder on birds.