The cassowary, the largest bird in the world after the ostrich, has a booming call to match its bulk. New research suggests that the birds communicate with low-frequency infrasound, a rarity among terrestrial animals. (Only elephants are known to use it.) Infrasound would be appropriate for this solitary animal because the sound carries well through long stretches of dense jungle, the researchers say.
Conservation biologist Andrew Mack of the Wildlife Conservation Society and Josh Jones of the University of California, San Diego, recorded cassowary calls in the jungles of New Guinea. The calls dip down to 23 Hz, just at the threshold of human hearing, they report in the October issue of the journal Auk.
The finding may shed light on the purpose of the cassowary's prominent headpiece, or casque. Scientists have theorized that the casques may somehow amplify the birds' calls. But the casques are too small to amplify such deep tones, says Mack, who now suspects that the casques are involved instead in receiving signals. The horny exterior and interior dark "sludge" could act like a boundary-layer microphone, Mack says, if the casque somehow vibrates or connects to the inner ear. He has yet to put this hypothesis to the test, however.
The research should help both conservation and science, says Mack, who is now developing an acoustic monitoring system to keep track of cassowaries. He predicts that understanding sound production and reception in these primitive birds will provide insights into crested dinosaurs. Dinosaur expert Tom Holtz of the University of Maryland, College Park, agrees that if cassowary crests are indeed involved in communication, it's possible that crested dinosaurs such as the cassowary-sized oviraptors "could have used their crests in some sort of sound system. ... This new study is getting me thinking about that."