[Coen] Elemans, the study’s first author, now is a postdoctoral researcher in biology at the University of Southern Denmark. He conducted the study with Franz Goller, a University of Utah associate professor of biology; and two University of Pennsylvania scientists: Andrew Mead, a doctoral student, and Lawrence Rome, a professor of biology.
To conduct the study, the biologists measured vocal muscle activity in freely singing birds and made laboratory measurements of isolated muscles.
They found the zebrafinch and European starling can contract and relax their vocal muscles in 3 to 4 milliseconds, or three-thousandths to four-thousandths of a second, which is 100 times faster than the 300 milliseconds to 400 milliseconds (three-tenths to four-tenths of a second) it takes for humans to blink an eye, Elemans says.
The birds’ vocal muscles move structures analogous to “vocal folds” in humans. The muscles change the position and stiffness of these folds to alter the volume and frequency of the sound.
Superfast muscles can produce mechanical work or power at more than 100 hertz (times per second) and these superfast vocal muscles at up to 250 hertz, which means the birds can turn elements of their song on and off 250 times per second, Elemans says.
© 2009 ION Publications LLC
We could not grasp this fact about muscles were it not for concepts and methods developed by a line of scientists going back to the 1600s and beyond: Newton’s definition of force; Watt’s definition of power; scientists’ ideas and discoveries on repetitive motion, “work,” sound, and more. At one point, people had to develop the idea that sound was a disturbance in air (and other media), then prove it. Such knowledge was a prerequisite to applying the concepts of force, power, and work to sound. What’s more, people had to discover that air was substantial, that it had mass, weight and density. (No mass, no force.)
As always, the hierarchy of knowledge is at work.