Bats use echolocation to hunt. But they also sing to woo females and mark their territory.
The recording you can listen to here is from the Pipistrellus nathusii, a small European bat (see photograph). The actual sound is ultrasonic – so very high – but it has been slowed down so the frequencies are audible for humans.
What is the bat actually/potentially saying:
Nobody has learned to speak fluent bat, but Virginia Morell says a team of researchers from the Czech Republic recorded and analyzed nearly 3,000 recordings of P. nathusii at 33 different places in southern Bohemia, and they think they’ve got the gist. The song, they say, opens with a hello, then a gender identification, then some geographic information, then a “let’s talk” section.