Published: 6/12/2021 8:57:51 PM
Spring and early summer are times when the air is filled with bird song. Even people who don’t consider themselves “birders” often appreciate the sounds of birds as a nice backdrop to their surroundings. It’s perfectly fine to just enjoy the sounds, but keep reading if you are interested in learning more about who the singers are and how they do what they do.
Most bird singing is done by the males as part of spring courtship or territorial pronouncements. It seems that females are more attracted to strong singers, perhaps indicating a healthier and more robust mate.
During the height of the “dating time” there is a wide variety of vocalization that comes out of the mouths of birds. If you have a discerning ear and a patient teacher, i.e. someone who knows more about bird sounds than you do, you can learn to distinguish various species of birds from each other by their sounds. That is also how a bluebird finds another bluebird and not a blue jay. Like a child who can distinguish her mother’s voice from that of other women in a crowd, birds find their kind, in part, by sound.
So how is the vast array of whistles, twitters, tweets and gorgeous melodies produced? Birds have a unique sound organ called the syrinx located at the base of the trachea where it splits to enter the two lungs. Sound is caused when air comes down the windpipe and vibrates the membranes within the syrinx. The sound is modified by pairs of muscles which a bird controls to create whatever variety of sounds are characteristic of its species. The number and configuration of the muscles is one of the things that contributes to the variety of sounds that are possible. Pigeons, known for their gentle cooing, only have one pair of syringeal muscles, while most song birds have at least three pairs. Six or more pairs of muscles enable virtuosos such as catbirds and starlings to have a more extensive repertoire.
The branched aspect of the syrinx also enables birds to create two different sounds at the same time. This is something that humans cannot do and is one of the other reasons that birds are able to make such a wide variety of sounds. Extreme examples of this occur when a single thrush creates ethereal flute-like duets that echo through the evening woods.
Still, how does a bird use its muscles to make the proper sound? Extensive research has been done on the development of bird songs and calls. It has been determined that both instinct and learned behavior play a role in song development. Depending on the species, one strategy may be more prominent than the other.
There are also different phases of learning. The first happening when a chick is still in its nest, during what scientists call the “sensitive period”. This is why the birds with more complex songs are the ones that are born naked and helpless, needing to spend more time in the nest to develop and thus having a longer time to be hearing the sounds of their parents and learning their species songs. Sounds made by precocial young like ducks or shorebirds who are able to be up and about shortly after hatching, and song birds who aren’t exposed to parental songs still make innate sounds. But the development of complex vocalizations comes from extensive tutoring and extended learning in later phases.
That brings me to my favorite bird, the mockingbird. These gray and white birds are not much to look at but can stop me in my tracks when I hear them. Because of an open-ended learning period, they continue to learn and repeat the sounds of other birds or sounds such as car alarms. How they do this is still not completely understood but it involves a complex interaction of physical structures in the syrinx, ear and brain, chemical triggers and hormones and individual experiences. The interaction of all of those elements, enable a mockingbird to emit the songs of 15 or 20 different bird species (or more) in rapid succession. It’s hard not to be in awe and enjoy that music.
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