Basso profundo

Natural History, March, 2007 by Rebecca Kessler

Blue whales, the biggest creatures on Earth, have the deepest voices: most of their vocalizations are pitched far too low for people to hear. Their songs repeat a series of eerie tones, blips, and creaks and may carry on for hours or even days. To human ears, the alien, barely audible songs are all but indistinguishable. A new study shows, however, that the leviathans sing several variations on the "blues," each correlated with a particular region of the sea.

Mark A. McDonald, an acoustician at Whale Acoustics, a company in Bellvue, Colorado, and two colleagues examined thousands of sound spectrograms computed from bluewhale songs recorded around the world since 1959. They found they could visually classify the spectrograms into nine distinct groups, each corresponding to a particular geographic region.

Blue whales of both sexes make short calls, but only the males are known to sing, suggesting the songs may enable them to attract mates or advertise their presence to other males. (Under certain conditions their songs can travel thousands of miles, communicating to other whales across vast ocean distances.) If so, each song group may be characteristic of a particular blue-whale population: after all, mating calls should attract compatible mates.

Songs, McDonald's team proposes, could become a convenient, noninvasive, tow-cost way for biologists to keep track of blue-whale populations and subspecies--though distinguishing animal groups by their behavior instead of their physical or genetic characteristics remains controversial. (Journal of Cetacean Research and Management)