Brimful Bill

 How many of us have had our parents exhort us not to talk when our mouth is full? Not only is such behavior bad manners, but our speech can become quite unintelligible, as food gets in the way of our tongue and lips, as they try to perform their nimble job of shaping sounds. Our speech and song is produced by the vibrating vocal cords in our larynx, which is then modified and shaped by muscles in our throat, nasal passages, tongue, and lips. It is a complex process that allows us to create a very wide variety of utterances. It gives rise to many kinds of sounds.

Several years ago I watched a goldfinch at the bird feeder, filling its beak with seeds, crunching the hulls off, as it shifted the particles around inside its beak, with its dexterous tongue. As I was watching, I heard a goldfinch song and looked around to see if another one was nearby, but the one at the feeder was the solitary goldfinch in the area. It dawned on me that this bird was singing at the same time that its bill was full. It seemed as if it had violated the etiquette of not singing with a stuffed bill; yet its song—unlike what emanates from a human's full mouth—was clear and clean. What was going on?

A visit to my bird books soon gave me the answer. A bird's song is created in its syrinx (analogous to our larynx), which is situated well down its throat, at the entrance of its two windpipes (tracheae). At the junction of each side of the syrinx and its adjacent trachea are a set of tiny, complex muscles. Vibration of thin membranes (like our vocal cords) creates sounds that are then manipulated and altered by these muscles. A bird's throat and mouth muscles play no role in its song—hence they can independently do their feeding job, without interfering in their singing.

This song mechanism is quite amazing. Virtually all of the air exhaled through a bird's syrinx is used for singing. In contrast, we humans use only about 2% of our lung air in vocalizing—which is why these little critters can sing so fully and loudly. Furthermore, a bird can literally sing a duet with itself, as air exhaled from each windpipe flows across the muscles on each side of its syrinx. The complex song of a thrush is an example of this self-duet. Two songs at once! In fact, a bird is even able to vocalize through one side of its syrinx as it breathes through the other. That beats the feat of a human ventriloquist!

All mammals are outfitted with a larynx, rather than a bird's intricate syrinx. I guess that means all mammal mommies urge their children not to speak with a full mouth? What other kinds of lessons of etiquette do bird mommies teach, when their kid's bill can be full to the brim and still sing out clearly and beautifully?