You know what they say: Birds of a feather flock — and migrate — together.

Fun fact: As of Oct. 8, ~43 million migratory birds have flown over Louisville this fall on their way south for the winter.

However, not all of them will make it to their wintry destinations. The Smithsonian estimates that 300 million to 1 billion birds are killed each year due to collisions with lit buildings.

That's why the Louisville Audubon Society is encouraging Derby City to turn off the lights during peak migration in the spring and fall: April and May + September and October.

It's called Lights Out Louisville. Here's what to do, from 11 p.m. to 6 a.m. each night — you could say a little bird told you:

Turn off unnecessary lights both indoors and outside
For outdoor lighting that is necessary, use a motion sensor and keep the lights pointed downward
Close your blinds, curtains, and shades
Use warm-colored bulbs — avoid white and blue colors

Birds usually begin to migrate 30 to 45 minutes after sunset, with most taking to the skies two to three hours afterward.

If you're ready to take off and do your part, sign the pledge to join the cause — there's even a separate pledge for businesses and organizations — or make a tax-deductible donation to the Louisville Audubon Society. A donation of $10+ gets you a free sign for your yard or window to help spread the word.

Bonus: Want to know which birds are currently migrating? Check out BirdCast to see the list, plus learn how many birds flew over Louisville last night.