This is bird note. Ornithologist Bill Evans has helped us better understand the sounds

that birds make as they migrate at night. Known as nocturnal flight calls, many

species can be identified based on their signature sound, like this green heron.

Using special handmade microphones left outside overnight, Evans, his colleagues, and many volunteers, recorded countless nocturnal flight calls

to catalog and identify the sounds. But we're still working to understand these calls.

Some are very similar to each other. Others have never been identified, some of the many modern-day

mysteries that biologists face. But for now, take a moment to revel in the beauty of the calls that birds make at night

while flying hundreds or even thousands of feet in the air.

This clip is from a six-hour recording of squeaks, whistles, and peeps from thousands of birds

passing over a hayfield in central New York State.

You'll hear a few crickets, too.

Learn more about nocturnal flight calls and how you can record them on our website, birdnote.org.

I'm Michael Stein.