A scientist from outer space scanning the earth for life forms might exclaim “There be whales here.” For the most powerful voice on our planet belongs to the blue whalethe largest animal ever to have lived on the planet. Comparable in sonic energy to the twin booster rockets of the space shuttle, the blue whale’s moan can cross an ocean and echo from the other side.
Such long-distance calls also represent the first infrasound of biological origin accurately described. Nonbiological sources of infrasound abound, including thunder, air turbulence, jet engines, volcanoes, earthquakes on land, and waves and ships in the ocean. In the early 1950s, with new electronic underwater listening devices spun-off from World War II research, scientists recorded infrasonic pulses of sound. Electronics revealed one-second-long tones at 20 Hz, about the lowest bass humans can hear. First thought to be Russian submarines, then a whale’s heartbeat, scientists finally realized the sounds were the vocalizations of fin whales.
Fin and blue whales belong to the order Cetacea, which also includes killer whales and sperm whales, as well as dolphins. But the blue whale and its relatives, such as the right, fin and humpback, all lack the teeth so obvious in killer whales, for example. They eat small crustaceans, filtering them from huge mouthfuls of water with a plate called baleen. Baleen, made of a material like our fingernails, gives this group its name.
The mode of eating is not the only difference between toothed whales and baleen whales. Baleen whales’ eating habits require them to migrate long distances. The humpback, for example, mates in Hawaiian waters and feedsonly in the summernear Alaska. Baleen whales also differ in growth and social structure, both of which affect their means of communication. Besides being the biggest animal, blue whales get big the fastest. A blue whale calf grows by 175 pounds and more than an inch a day. She only nurses for six monthsat which time she’s at least half her adult sizeand sexually matures in less than five years.
The relationship between a mother and her calf, however short, is the longest lasting one in baleen whale society. Although groups migrate, feed and breed together, they remain fluid, and a particular group structure may last only hours. No well-studied species of baleen whale forms monogamous mating pairs, so when males find females, the competition heats up.
Male whales, like males of many other species, appear to advertise themselves vocally. But no other animals do so in such an elaborate way. Humpback whales sing a complex song, which can last up to 20 minutes. The songs comprises several parts, each of many notes, ranging from a bass rumble to a shrill squeak. Each male sings the song over and over, part for part, note for note, sometimes spending hours in a single concert.
Dolphins identify themselves and each other with signature whistles. But scientists have yet to determine whether baleen whale songs identify an individual. Whales singing with any one group, however, all sing slight variations on a single song. This observation could lead to the conclusion that the song is genetically hardwired, but for the fact that the song changes over time. Gradually throughout the singing season, note by note, the song evolves, with the result that a given community song may bear little resemblance to the song of a year before. This change does not come about by a complete change in the makeup of the group, as individual whales can be identified by markings from year to year.
What are whales doing with their songs and infrasonic calls? No one knows for sure. The songs appear important in mating, and infrasonic calls may allow whales to keep in touch over long distances. One scientist estimated a fin whale could pick up a broadcast by another fin 3,000 miles away. Infrasonic calls travel such distances intact under water because the sound waves bounce off the under surface of the water, as well as off boundaries between cold and warm water. So instead of spreading as sound does in air, infrasound travels in a corridor, dissipating much less quickly than it would in air. Furthermore, the wavelength of a particular pitch increases more than four times in water, making it even better as a long-distance signal.