If you sleep with the window open at night or enjoy waking up before the rest of the world, you have probably discovered that the hour before a spring dawn can be magical. That’s when songbirds raise their voices in what birders call the dawn chorus. Larger birds like robins, blackbirds and doves are the early birds, with sparrows and finches joining last. The first birds to sing are the ones with the largest eyes because they can detect predators better in low light.
Birds vocalize to advertise themselves as attractive mates, claim a nesting territory, communicate with their young, orient themselves during flight, and warn other birds. Vocalizations are made possible by a special organ called the syrinx, a bony structure located between the windpipe and the bronchial passages to the lungs. When birds pass air over the syrinx, membranes lining the walls of the syrinx vibrate at different frequencies, producing different sounds.
Birds have two general types of vocalizations: songs and calls. Songs are melodious and can be long and fairly complex. In contrast, calls are louder and shorter, often just a single note, and are used to alarm other birds or to communicate while in flight. A robin that has been startled by a predator or a house sparrow whose nest is being attacked issues a harsh alarm call as opposed to the song it sings in the morning.
With practice, we can identify birds by their songs, and most often we’re hearing the male. While they have a species-specific song, some sounds are uniquely their own so that nearby birds can recognize them as individuals. Thrashers, mockingbirds and catbirds are excellent mimics and can be mistaken for other birds. They pick up phrases they hear and incorporate them into their own repertoire. The male northern mockingbird can string together a series of more than 100 different phrases during the course of his lifetime. The American crow can learn to mimic a variety of sounds in captivity.
Mockingbirds also sing at night, especially if they don’t yet have a mate. Some birders claim that by listening to a mockingbird, it’s possible to identify other species that live in a particular area. Another bird that sings after dark is the whip-poor-will, which can repeat its name more than 1,000 times consecutively in one night.
The way that birds learn to sing parallels the way human children learn to speak. The young bird first memorizes the song of the parent or other adult, then learns to do a poor imitation of the song. In some species like the northern cardinal, oriole, starling and house sparrow, both the male and female sing. As young birds mature, they refine their vocalization until they “get it right,” and eventually the song becomes crystallized. Parental attentiveness plays a role in song clarity.