Massive migrations of birds occur at night across much of the Americas. Many species give short vocalizations as they fly, presumably for contact with other migrating birds, to work out flight spacing to avoid mid-air collisions, and for echolocation. Thousands of calls a night can be heard in some locations. Much of this migration is well above the average altitude of the terrain and not easily heard by ear, but a microphone can be built or purchased to help tune in and amplify flight calls of migrating birds. One can do this for listening pleasure or go a step further and document the number of calls and species of birds flying over a specific location. Once your recording system is functional it can be integrated into regional networks of recording stations to help produce a bigger picture of bird migration and begin logging data on regional bird migration patterns. Long term monitoring provides a unique index for changes in bird populations.