Two years ago, musician Stuart Hyatt had no idea that the endangered species called the Indiana bat would be such a huge part of his life. But then in 2018, he chaperoned his 10-year-old son on a weekend school trip to the Great Smoky Mountains. On the final night of the trip, the group took a walk into the woods to observe bats. “We could see them, but we couldn’t hear them, because bats echolocate at a frequency higher than what our ears can hear,” he told Earther. But then, a park ranger pulled out a small, silver device and pointed it at the sky. By changing the frequency of the bat noises, the device transformed them into something audible to the human ear. The experience set Hyatt onto a multi-year mission to record the creatures. Thanks to a grant from National Geographic, Hyatt was able to travel with scientists to observe and record bats in rural Indiana. He focused on the Indiana bat, which is losing ground to climate change and disease. Rising temperatures are degrading the caves, marshes, and forests where the bats live and a fungal infection called white-nose syndrome have further hurt their numbers. There are only 500,000 of the species left in the U.S., and as global warming worsens, the population may continue to dwindle. By using a variety of specialty recorders and other equipment, Hyatt was able to record the bat sounds and bring them down to frequencies humans can hear. He then enlisted a group of composers, and handed them the field recordings to transform into music. The culmination of all of this work is an album called Ultrasonic: Making Music with Endangered Indiana Bats. When he passed over his recordings, Hyatt didn’t instruct the other musicians to specifically make pieces that reflect the plight of the endangered Indiana bat. But there are signs of the species’ hardship throughout the music. One track called “Night Swimming,” made with multi-instrumentalist Jefre Cantu-Ledesma, has an eerie melancholy about it that reminds you that these creatures are dying out. And a more hopeful piece named “Dusk Tempi,” composed by ambient recording artist Eluvium, mixes the bat sounds with cascading violin lines, creating an almost heavenly effect. You can listen to Ultrasonic: Making Music with Endangered Indiana Bats on Spotify here.