Parents have often been heard telling kids not to caw like a crow. Now, a new study by University of Utah ornithologists has shown a striking similarity between the birds signature caw caw call and a low, raspy sound produced by humans.
London, Aug 29 : Parents have often been heard telling kids not to caw like a crow. Now, a new study by University of Utah ornithologists has shown a striking similarity between the bird's signature caw caw call and a low, raspy sound produced by humans.
As part of his study, Franz Goller and his team took high-speed video shot from inside a crow's voice box.
"We used an angioscope, which are small optic fibre devices that doctors use to investigate blood vessels in humans," said Goller, whose team shot the video.
Goller said he first used the technique in the mid-1990s. At the time, it allowed him to solve the mystery of how the vocal organ of songbirds works.
The syrinx is the bird equivalent to a human's larynx and is remarkable in that it is essentially a double voice box. Whereas in humans air passes through a single "valve", in songbirds each lung is hooked up to its own valve.
Earlier videos revealed that sound was produced when muscles pulled two heavy folds of tissue on either side of the valve apart. Outrushing air set the folds of tissue vibrating, just as it happens with human vocal cords.
But this all happens very quickly, so in the early videos the researchers could not discern the details of how this was happening.
In the new experiment, Goller used newer angioscopes that are able to take better-quality high-speed video images. He and his colleagues filmed the inside of a hooded crow's syrinx.
To activate the syrinx, they pressed on the anaesthetised crow's chest, pushing air out of its lungs, through the double voice box and into the trachea, which produced the crow's signature caw.
The video further showed that the cawing was produced when the valves opened briefly, then remained shut before briefly opening again, and at a speed which was impossible to see without high-speed cameras.
Goller said the mechanism is very similar to a hoarse, raspy sound produced by humans called "vocal fry" - a very low frequency crackling, sounding a bit like static radio noise.
"Vocal fry is produced when the human larynx opens very briefly for a pulse then has long closed phase," Goller told New Scientist.
"It looks like birds do the same, but with two openings," he said.
The findings appear in the Proceedings of the Royal Society B.
ANI