Posts Tagged ‘syrinx’

Vocal Virtuosity

October 11, 2019

This post is based on “The Genius of Birds”, a book by Jennifer Ackerman. The vocal virtuosity of birds is evident. What was only discovered fairly recently was special organ birds have that enables this virtuosity. This unique instrument is called a syrinx. It took a long time for scientists to learn its details because the syrinx is buried in the bird’s chest, where the trachea splits in two to send air to the bronchi. Only recently did a researcher produce a stunning high-resolution three dimensional image of the organ in action, using magnetic resonance imaging and microcomputer tomography.

The syrinx is made of delicate cartilage and two membranes that vibrate with airflow at super fast speeds—one on each side of the syrinx—to created two independent sources of sounds. Gifted songbirds such as the mockingbird and canary can vibrate each of their two membranes independently, producing two different, harmonically unrelated notes at the same time—a low-frequency sound on the left, a high-frequency sound on the right. These birds can shift the volume and frequency of each with breathtaking speed to produce some of the most acoustically complex and varied vocal sounds in nature. In contrast, when humans talk, all of our pitch, all the harmonics of our vocalizations, move in the same direction.

Songbirds such as European starlings and zebra finches can contract and relax these tiny vocal muscles with sub millisecond precision at more than a hundred times faster than the blink of an eye. The winter wren is a bird known for its swift song delivery. It sings as many as 36 notes per second, which is much too fast for our ears or brain to perceive or absorb. Some birds can manipulate their syrinx to mimic human speech.

Not surprisingly, birds with a more elaborate set of syringe muscles can produce more elaborate songs. The mockingbird has seven pairs that allow him to perform his vocal gymnastics over and over with little effort. This can be 17, 18, 19 songs per minute. Between the notes, he takes tiny breaths to replenish his air supply.

Of course, more than the syrinx is involved. Songs must be initiated and coordinated with the bird’s brain. Nerve signals from an elaborate network of brain areas control each of the muscles, coordinating nerve impulses from his left and right brain hemispheres to the muscles of the two halves of his syrinx, creating just the right airflow in each necessary to produce the hundreds of different imitated phrases he sings.

Scientists use sonograms or spectrograms to assess the accuracy of this sounds. These are visual printouts of sound (with frequency or pitch on the vertical axis and time on the horizontal axis) that scientists use to detect subtle differences in birdsong. Sonograms comparing a prototype song and the mockingbird’s copy show that the imitator sings nuthatch and thrush and whip-poor-will with almost perfect fidelity. When a mockingbird sings a cardinal’s song, it actually mimics the muscular patters of the cardinal. If the notes of his model fall outside his normal frequency range, he substitutes a note or omits it, lengthening other notes to match the song in duration. If he’s facing a too-rapid-fire delivery of notes such as a canary’s, he clusters the notes and pauses to breathe while maintaining identical song length.

The mockingbird is not the only mimic. A cousin Mimidae, the brown thrasher, can mimic ten times the number of songs a mockingbird sings, thought not with as much accuracy. European starlings are also accomplished mimics, as are nightingales, which can imitate some 60 different songs after hearing each only a few times. Marsh warblers sing a wild, urgent, international pastiche of a song peppered with the tunes of more than one hundred other species.

Some birds, the African grey parrot, the mynah, and the cockatoo excel at imitating human speech. There are a few others in the corvid and parrot families, parakeets being one example.

It’s quite an accomplishment for birds to imitate human sounds. Humans form vowels and consonants with their lips and tongue, which are among the most supple, flexible, and indefatigable parts of the human body. For birds, with no lips and with tongues that generally aren’t used for making sounds, it is a tall order indeed to take on the nuances of human speech. Parrots are unusual in that they use their tongues while calling and can manipulate them to articulate vowel sounds.

Parrots have been known to teach other parrots to talk smack. People have reported wild cockatoos swearing in the outback. An ornithologist speculated that the wild birds had learned from once-domesticated cockatoos and other parrots that had escaped and survived long enough to join a flock and share words they have picked up in captivity. Ms. Ackerman comments, “if true, a fine example of cultural transmission.”