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. Using special handmade microphones left outside overnight, Evans, his colleagues and many volunteers recorded countless nocturnal flight calls — and not all of them have been identified yet. In this show, revel in the beauty of the calls that birds make as they fly high in the air.More info and transcript at BirdNote.org. Want more BirdNote? Subscribe to our weekly newsletter. Sign up for BirdNote+ to get ad-free listening and other perks. BirdNote is a nonprofit. Your tax-deductible gift makes these shows possible.