Bird Songs are Increasing in Spring
Ro Wauer, Feb 23, 2003, The Victoria Advocate, © 2003
Bird songs are all around during these spring mornings, a sure sign that warmer days are just ahead. Although a few bird species, such as cardinals, Carolina wrens, titmice, and mockingbirds, have been vocalizing almost since the first of the year, many other species are joining the bird chorus as springtime progresses. All our doves have begun their varied songs, red-shouldered hawks are screaming overhead, chickadees are singing aloud, and our welcome purple martins are brightening the dawn skies with their mellow songs.
Springtime solicits the greatest amount of bird song than any time of year. That is when birds are signaling their neighbors to stay away from their territories, attracting mates, and, once mated, to stay away from their nesting grounds. A bird's song also contains details about individual identity, allowing others to recognize the individual. Song length, frequency range, and the order and length of the song phrases provide the necessary clues. Experiments with several colonial birds, such as terns and gulls, show that individuals respond to the taped calls of their partners but not to the calls of nonmates. Vocal recognition between parents and offspring is especially important.
In closely related species, vocalization might be the only way individuals can make distinctions among themselves. Examples include several of the flycatchers that look so similar, such as Couch's and tropical kingbirds and willow and alder flycatchers.
Researchers have shown that unrelated species that live in the same habitats have songs that are more similar than closely related species that live in different habitats. Forest birds typically have songs or calls markedly different from species common to open country or grassland habitats. Deep forest birds, such as thrushes, generally produce pure tones with little modulation or harmonic structure and lower frequency than birds of open country. Grassland birds have evolved songs or calls that have high-frequency ranges and contain rapidly repeated buzzy trills and complex modulations. High-frequency notes travel more rapidly than notes of low frequency.
The question of whether the bird songs are inherited or learned is one that many researchers have studied. And the results vary. Many birds, such as meadowlarks and cardinals, learn their songs from other meadowlarks and cardinals. When raised by foster parents, they sing abnormal songs. Other birds, such as song sparrows, sing normal songs no matter where they were raised.
Researcher David Mizrahi suggests that young birds learn their songs in four stages. The first two are silent ones. The first lasts two to twelve months while the youngsters are learning structure and pitch variation. In the second step, lasting about eight months, the youngsters learn syllables or phrases. Once those two stages end, the young bird begins to practice, listening to themselves, matching what they hear with what they memorized during the earlier stages. The final "crystallization" stage is when the bird's songs are stabilized and transformed into one that others of the same species will recognize.
For some species, such as mockingbirds, learning new song phrases continue throughout life. The diversity of songs in their repertoires can change throughout and increase as they grow older. But how or why vocal mimics select the songs that they imitate is unknown.
Springtime is when we can hear an amazing assortment of bird songs. While the majority of the songs are typical songs that can be expected from whichever species is vocalizing, we can also hear bird songs from youngsters that are not yet fully prepared to defend a territory and mate.