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Vocal Development

Young birds develop their singing abilities in strikingly different ways, depending on their species. For example, songbirds such as wrens, sparrows, thrushes, and warblers learn their songs from others. In contrast, flycatchers and their relatives don't need to learn their songs--they inherit all the genetic instructions they need to sing the appropriate song.

Inherited abilities--flycatchers

Flycatchers and their relatives are called suboscines, a group of more than 1,000 species that includes pittas, broadbills, antbirds, cotingas, manakins, and others. Studies show that young flycatchers have the innate ability to sing their species' song. 

In one experiment, for example, young Alder and Willow flycatchers were taken from their nests when they were about 10 days old. Researchers attempted to teach the birds the incorrect songs. They played recordings of a Willow Flycatcher's FITZ-bew song to the young Alder Flycatcher. They played the fee-BE-o song of an Alder Flycatcher to the Willow Flycatcher. Despite this confusing situation, both birds developed normally and sang their own species' song.

Left to right: Alder Flycatcher, Willow Flycatcher

Studies of Alder Flycatchers in the wild show that as soon as they leave the nest (at 14 days), they are already uttering a scratchy rendition of the fee-BE-o-song, which they use to keep in contact with their siblings and possibly their parents.

Learned skills--songbirds

Songbirds, or oscines, are a worldwide group of more than 4,600 species, including orioles, warblers, wrens, thrushes, and other birds known for their beautiful singing. Unlike suboscines, all songbirds that have been studied so far must learn to sing.

Classic studies of the White-crowned Sparrow showed that a nestling taken from a nest at eight or nine days of age and raised alone in a laboratory would develop an abnormal song. However, young White-crowned Sparrows housed with a "tutor" (a singing adult White-crowned Sparrow), learned their songs from that bird.

Young White-crowned Sparrows don't just learn any song they hear, however. It is as though they are predisposed to learn their own species' song. If housed with a Song Sparrow and a White-crowned Sparrow, the young bird will learn the song of its own species. If only housed with a Song Sparrow, however, White-crowned Sparrows sometimes learn to sing as a Song Sparrow does.

All songbirds are equipped with a more complex sound-producing organ than suboscines have. Called the syrinx, this structure is what allows songbirds to make such a bewildering variety of whistles, trills, and warbles. Interestingly, not all songbirds produce complex melodic songs. Crows, for example, use their syrinx to produce only coos, caws, rattles, clicks, and grating noises instead of a melody.

Window of learning

Most songbirds seem to have what is called a "sensitive period" for song learning. It is during this brief period that birds are best equipped to memorize details of a tutor's song. For the White-crowned Sparrow, this period is between about 15 and 50 days of age. After that, learning becomes more difficult.

Fledgling White-crowned Sparrows begin to practice singing shortly after leaving the nest, at about three weeks of age. Apparently, they recall the sounds they heard during the sensitive period, and try to match it with their practice singing, called a subsong.

Subsongs begin very quietly and become louder, more persistent, and more structured over time. Corrections to the practice song eventually result in a perfect copy of the remembered song. Like humans, songbirds must be able to hear themselves vocalize during the developmental process in order to sing properly.

Big repertoire or small?

The number of different kinds of songs that a bird sings depends on the species and, in some cases, age. The Eastern Phoebe sings just two songs: fee-bee and fee-b-be-bee, alternating between them. In contrast, birds that are capable of learning throughout their lifetimes, such as Northern Mockingbirds, may accumulate hundreds, adding more songs to their repertoire every year.

The chart below shows a comparison of repertoire sizes for a few common birds. The numbers indicate averages for each species, since the repertoire size may vary depending on geographic location, lifestyle, or age. Repertoire size does not necessarily indicate the complexity of vocalizations. For example, each male Indigo Bunting sings just one complex song, but he produces this song by combining six to eight notes in different ways.

Changes over time

Many songbirds keep learning even after setting out on their own as a youngster. The songs of a particular bird can change over time. During his first nesting season, for example, a young male Indigo Bunting sings an odd song unique to himself, and typically different from his father's. Over time, however, he usually changes his song to match details of his neighbor's song. If you listen to Indigo Buntings in different places, you may notice that neighboring males have songs similar to one another, but different from those in more distant locations.

Mimics--champion singers?

Some birds are adept at mimicking the calls of other species, and add to their repertoire throughout their lives. Northern Mockingbirds may eventually learn more than 200 different songs; Brown Thrashers may sing as many as 2,000!

Other species have the uncanny ability to mimic manmade sounds and even human speech. The best known of these--the parrots--aren't even members of the songbird group

For more information on why birds use mimicry, visit the Bird Sounds FAQ.

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