Chirping is the second way to communicate in Journey, other than writing in sand. You can chirp by pressing or holding Circle, the longer you hold it, the bigger the radius. When you chirp, a transparent dome of sound appears with the travelers or companions randomly generated glyph.
Chirping can also help you find companions if you get separated from each-other by when they chirp, a white light on the screen shows on which side of the screen they are on.
Chirping can only be used as communication by using Morse Code.
And Chirping can also recharge a companions scarf so they can fly longer, use this with a fellow companion when flying side by side for longer flying. It can also quickly activate the stones near the Ancient One's shrine near the end of a area.