How do birds chirp?

Okay, I’m still obsessing on my catbirds.

I see the parent catbird going from perch to perch with something in its beak, presumably a tasty morsel for the baby catbirds (kittenbirds?). It is also chirping away (why? signaling the babies? signaling other birds) – but its beak stays firmly closed around the morsel.

Does the chirping happen further back in its throat, or what?

A bird’s vocal apparatus is very different from that of humans. The sound-producing organ, the syrinx, is deep inside the chest where the trachea (windpipe) branches to go to the lungs. Birds don’t need to open their mouths to produce sounds, though they often do in order to project the sound farther.

The musculature on the two sides of the syrinx is under independent control, so that some birds are able to sing two different songs at the same time.

Excellent link! Thanks, Colibri!