The birds are singing!
Birdsong is a favorite aspect of spring and summer. While we might romanticize the singing as expressions of joy, it's serious business for the birds.
Although virtually all birds communicate by making sounds, passerines (the "song birds") excel at making complicated music. Bird "songs" are more complex than bird "calls," often having several distinct sections or phrases.
Most bird species evidently hatch with an innate, rough template of the primary song their species sings. It appears that hatchlings begin warbly subsongs, the bird equivalent of baby talk, when less than three weeks old. During the young birds' first spring and summer they hear the songs of the adult male in their home territory and learn the details of their song in the local dialect. They'll have learned a plastic "rehearsal song" by their first spring as an adult, then will fine tune their "primary song" that will last unchanged through the rest of their lives.
The babies of most species of birds can be taught to sing some variation of the wrong song.
That understanding about how birds learn to sing is based, in part, on research done with white-crowned sparrows. Since that landmark research, it’s been found that some species are hatched knowing the full song for their species.
Adult songbirds end up with a suite of songs; in a few species as many as 20. In addition to the primary song, most males sometimes sing a "secondary song." The song may change somewhat for those birds that sing through the winter, becoming a "muted song." A "whisper song" may be sung by males or females when it's dark, quiet, or rainy, or when the bird is uneasy.
Most species sing their primary song from one or more exposed, strategic perches. Some species add a showy, visible flourish, such as the raised bright shoulders of the red-winged blackbird.
In most North American songbirds it's the male singing the primary song. In some tropical species of birds, males and females sing in unison or in harmony as part of their courtship.
So, why do birds sing? Primarily, birds sing to pronounce their species and to define their territory. "I'm a white-crowned sparrow and this is my territory!" advertises to interested females and wards off competing males. It also teaches the chicks in the nearby nest what song they should sing as adults.
While this white-crowned sparrow was singing in the middle of the day, most songbirds sing their declarations from daybreak to early- or mid-afternoon, often starting up again at dusk. During the long days of summer, an individual male may sing his primary song several thousand times a day.
While we enjoy listening to birdsong and use it as a way of identifying unseen birds, it plays a critical role in birds’ lives.