Each spring and fall, about 5 million birds (from 250 species) migrate through Chicago. They’re often attracted by building lights and lighted glass areas—with fatal results.

We humans have long feared the dark. That’s where scary monsters hide and criminals lurk. So that’s why, for most of our history on the planet, we’ve been trying to dominate the night by filling it with light.

In many cases, illuminating our nights has worked. Crime often decreases by a significant percent, and the perception of safety soars.

But our penchant for eradicating the darkness has had its costs, too. Thousands of hatching sea turtles on Florida’s coast die every year by becoming disoriented by Miami’s lights. And Field Museum of Natural History volunteers annually collect thousands of dead birds—victims of collisions with brightly lit buildings and confusion caused by artificial light—from Chicago’s city sidewalks.

Lighting near the shore can cause sea turtle hatchlings to become disoriented and wander inland, where they often die of dehydration or predation. ©oksana.perkins/Shutterstock.com

That’s why Ian Cheney, a Brooklyn-based documentary filmmaker, asked himself the simple question, “Why do we need the stars?” In his 2011 film, The City Dark, he sets out to explore the science of darkness and investigates the effects of light pollution on our health and on the health of the natural world.

So before turning on your big yard light tonight, watch the movie trailer below.

Here’s to finding your true places and natural habitats,