The sounds that they're just describing and the ones you're currently hearing, the " chips, " " cheeps, " " zeeps, " " whistles" and " trills, " — these are the sounds of birds migrating at night.
科学快报-科学美国人2023Science Quickly, from SCIENTIFIC AMERICAN 2023
The sounds they're describing and the ones you're currently hearing, the " chips, " " cheeps, " " zeeps, " " whistles" and " trills, " —these are the sounds of birds migrating at night.