A little anatomy today. In Chicago when I was a kid of about 10, I was sitting on my home’s front porch when a parakeet landed on my head, obviously an escapee. A tame and lovely blue bird, I kept him for several years. I used to watch him warble (or whatever the semi-musical sound was he made) and was fascinated to watch the feathers of his throat stick out from their usual flat position. I thought there was a hole in his throat that he sang through. Turns out it’s the syrinx making the throat vibrate.
Let’s look at the inxes and ynxes involved here. In mammals, the pharynx is the space in the back of the throat leading to the respiratory and digestive systems. The epiglottis, a flap in the back of the pharynx, prevents food from going into the glottis, the opening into the lungs. Below the pharynx is the larynx which consists of a number of cartilages and is held together by ligaments and muscles; the larynx, commonly termed the voicebox, contains membranous folds which produce sounds as air passes over them, hence the moos of cows and the barks of dogs.
Birds have an oropharynx but no epiglottis. A bird’s tongue shape and grooved mouth aid in food movement past the tracheal opening, the glottis, and into the esophagus. The syrinx, Greek for pan pipes, is the vocal organ of birds. Instead of being located at the bottom of the pharynx as in a mammal’s trachea, the syrinx is located where the trachea branches into two bronchi, each entering the lungs. Air flowing over the membranes stretch and vibrate via the use of five to nine pairs of muscles, making sounds, amplified by the air sac surrounding the syrinx. The podcast BirdNote notes that “In many songbirds, the syrinx is not much bigger than a raindrop. Extremely efficient, it uses nearly all the air that passes through it. By contrast, a human creates sound using only 2% of the air exhaled through the larynx.”
As you would expect, the syrinx of birds varies considerably among species, being most complex in the songbirds (Passeriformes). The song structure can be very complex as the two sides of the syrinx can vibrate independently. In the Northern Cardinal, for example, the left side of the syrinx produces a low pitch while the right side produces the higher pitch. Also, birds are not restricted to singing while exhaling as we do, but can sing while inhaling. The Skylark can sing a song continually for up to 18 minutes.
Some birds do not have a syrinx, such as New World Vultures and syringes differ considerably among species and often between sexes of the same species, the male often having a more complex song or call than the female.
The syrinx, like feathers, is only found in birds. How the voice box switched from the larynx to the syrinx is unknown although there are a couple of ideas noted in an article in Science Daily.
(I’m not sure where the terms syrinx, larynx, and pharynx come from, but the inx suffix means “resembling.” Sphinx, the statue we all know, comes from the Greek sphinx meaning “strangling or closing up.” So maybe the inx and ynx endings refer to the closing and opening of the throat. Just my speculation.)