Ever wonder why some birds tweet, some sing, some quack, and the ones outside our bedroom windows at 5:00 in the morning caw?

A bird’s “voice” comes from the syrinx, which is the avian variety of the human voice box. The syrinx contains membranes that vibrate when air from the bird’s lungs are passed over them. But while the human larynx is positioned high in the throat, birds’ syringes (that’s the plural of “syrinx”) are located down closer to the chest, where the bronchial tubes branch off into each lung. That means that the syrinx has two sources of sound, one from each bronchus, which gives birds a wider range of vocal sounds than humans.

But even in the bird kingdom, life isn’t fair. The melodiousness and versatility of a bird’s voice is a product of evolution—the more and higher-developed muscles a bird has around his syrinx, the sweeter his song. Birds that don’t have to rely on conversing with others to find a food source, like ostriches and vultures, have no syringeal muscles. Ducks spend their days paddling around lakes and waddling along the shore, in clear view of one another, so they don’t need elaborate songs to attract a mate. A simple “quack!” and the shake of a tail feather is sufficient.

But birds that spend most of their time in trees need voices that carry, since all those leaves act as sound dampeners. And they also need distinctive sounds, so that sparrows can communicate with other sparrows. As a result, songbirds have from five to nine pairs of muscles around their syringes that squeeze out the tunes that serve as everything from a danger signal to a dinner bell to a love song.