In the deep ocean, giant mammals swim in sightless waters and find each other using mysterious songs. While the Navy has known about whale songs since the 1960s (at least), and sailors have long heard their eerie cries through the hulls of ships, it’s remained a mystery how whale songs were actually sung—until recently.
Land mammals such as apes have finely tuned eyesight with vivid color sensitivity. Human beings live in civilizations driven by visual communication. Such is not the case for these great mammals of the deep sea, whose beady eyes take a backseat to the world of sound.
Underwater, sound travels nearly five times faster than overland. Sound is essentially the vibration of particles forming into waves that travel through air or water, which the ears interpret as sound. The relatively higher density of particles in water means they are in closer contact with each other, thus having less distance to travel to pass on the vibration from one to the other, and so sound waves travel much faster. Marine mammals parley this sightless realm to their advantage.
Whales have adapted to this special environment, using sound to “see” and communicate beneath the waves. Since the Navy gave us the first recorded whale songs in 1967, scientists have learned how whales hear such sounds: they have ears specially outfitted with an air pocket; yet it remained a mystery how whales produced their enchanting songs. The Navy would continue its research into this unique ability and develop the technology of sonar.
Now, however, a new study has examined the larynx of whales that had died after being stranded and built computational models to uncover the mystery behind their vocal anatomy.
Baleen whales, in particular, are the largest mammals on Earth. Among them are the humpback, blue, and gray whales. The research team who conducted the study, published in the prestigious journal Nature, was led by Coen Elemans, from the University of Southern Denmark’s Department of Biology, and Tecumseh Fitch, from the University of Vienna’s Department of Behavioral and Cognitive Biology.
Examining the dissected larynx of humpback whales, they found the organ to be, in some ways, similar to those of land mammals; the larynx of baleen whales retains its key role as a vocal organ under the sea. Yet there were distinct differences. In particular, the researchers isolated the mechanism responsible for whale songs, which consists of several parts:
Whales have an elongated U-shaped apparatus called the arytenoid. Consisting of two horizontally oriented lengths of cartilage, this serves the purpose of changing the position of vocal cords in many mammals.
Nestled on top of the arytenoid lies a fibrous “cushion.” In whales, this can either be used in the respiratory position to blow air through their blowholes; or the phonatory position to cause a vibration that makes a whale song.
In the phonatory position, air from the lungs is captured in a laryngeal air sac which, they hypothesized, allows the recycling of air during their singing.
Also noteworthy, whales have a feature absent in land mammals: a set of “mysterious” nasal and oral plugs that protect the airways from water.
The area of this mechanism where the “cushion” and U-shaped arytenoid meet is the source of the vibration, causing the sound of whale singing. Powered by the whale’s explosive lungs, an aerodynamically driven vibration occurs in the cushion when in the phonatory position.
Testing further, they were even able to match the sound frequency which this part of the anatomy would generate with that of humpback whales. This matching was accomplished by constructing a computational model of the larynx that was able to successfully simulate the effects of this air-powered vibration and subsequent sound.
Their computer-generated predictions closely matched the natural vocalizations—the singing—of humpback whales.
“The first acoustic recordings of humpback whale song by Roger and Katy Payne in 1970 resonated with humanity profoundly, started the flourishing field of marine bioacoustics, and sparked global interest in marine conservation efforts,” Mr. Elemans said. “These recordings were so politically important then that they are aboard the Voyager space missions.”
