This is Bird Note.

You just heard the grunt of a comorant,

the whistle of a cardinal, and the song of a song sparrow.

Nearly all birds produce sound through an organ unique to birds,

the serencs.

The serencs is a set of muscles and membranes located

where the two branches of the bronchial tubes converge to become the trachea.

An adjacent air sac helps build pressure in the serencs.

In many songbirds, this whole song-producing apparatus

is not much bigger than a rain drop.

The serencs is extremely efficient at creating sound,

using nearly all of the air that passes through it.

Let's listen again to the limited vocal range of the comorant

whose serencs is controlled by only one set of muscles.

The cardinal, a familiar bird of central and eastern states,

creates its pure whistle by producing sound

in its left and right bronchial tubes simultaneously.

The song sparrow, like many other songbirds,

has five to seven pairs of muscles that govern the serencs.

It puts forth a cascade of trills and notes

as if singing a duet with itself.

For bird note, I'm Michael Stein.

...