Comment by ses4j

Many enthusiasts and scientists are recording and identifying birds from nocturnal audio recordings. Some references:

- https://www.facebook.com/groups/NocturnalFlightCalls

- https://github.com/HaroldMills/Vesper

- http://oldbird.org/pubs/fcmb/start.htm

- https://nightmigrants.com/main/page_home.html