The means and ends of these communications are most astounding to humans perhaps because we are accustomed to viewing communication as a sign of intelligence, and probably most people believe that humans are the only truly intelligent species on this planet. One way scientists attempt to quantify the intelligence of a species is to measure the ratio between brain size and body mass and compare it to that of a human. While no species matches human brain proportionately, some whale species come very close. Scientists do not agree on the exact level of intelligence of whales, but there are some truly astounding examples of whale communication that provide strong evidence in their favor.
Many species of whales hunt prey in groups called pods, and communication plays a vital role in their success. Some pods of humpback whales, including those from the Chatham Strait in Glacier Bay, Alaska, use a fascinating technique called bubble net hunting. When one member of the pod detects a school of prey fish it emits a feeding call that both the fish and the whale pod members respond to. The fish shy away from the feeding call while the pod members position themselves underneath the school.
Long before the internet and television, before Bell summoned Watson in that first telephone call, even before Marconi invented the radio and Morse the telegraph, whales were calling each other literally from opposite ends of the oceans. This amazing discovery was made using the US Navy's Sound Surveillance System (SOSUS) that was installed to track and monitor Soviet subs during the Cold War. It turns out that SOSUS can track whales just as well as it can submarines. SOSUS data showed that a single whale in the Atlantic Ocean could call to others across nearly the entire ocean. Long-term records have also showed that this distance has decreased over time as shipping traffic has increased. Scientists estimate that doubling shipping traffic has nearly halved the distance over which whales can effectively communicate. Researchers suspect that prior to propeller-powered shipping, whales could call across entire oceans and even from one ocean basin to another.
These long-distance communications are carried along a natural underwater network of acoustic waveguides. Sound traveling deep in the ocean is bent by changes in the speed of sound, just as light is bent when it enters the water. The speed of sound in the ocean depends on varying conditions such as temperature, pressure, and salinity. At certain depths and locations, sound waves travel along channels called "acoustic waveguides" because sounds waves attempting to radiate away from the channel are bent back toward it by changes in the sound speed around the waveguide. SOSUS relies on these waveguides to detect Russian submarines, and whales rely on them for communication and navigation. Like most natural systems on the Earth, waveguides are constantly evolving and are affected by the Earth's climate, so communication may have been very different during the last ice age than it is today.
The whales sing across nearly the entire range of human hearing with a vocal range no human could match. They lack vocal chords, so they probably create the sounds by circulating air through their respiratory systems. But during their singing they do not move their mouths, and no air leaves their blowholes either. Nevertheless, the whales' remarkable musical instrument can be heard as much as 20 miles away.
Their songs are organized in a "Russian doll" hierarchy beginning with single units or notes that are grouped in sub-phrases that last approximately ten seconds long. Two sub-phrases comprise a phrase that is repeated for several minutes as a single theme. When one theme is complete, the whales will sing another, and another, continuing for about thirty minutes. This collection of themes makes up a whale song that the male repeats frequently for hours or even days.
Researchers do not know the precise reason for the humpback whale song, but it is suspected to simultaneously attract females and ward off competitor males. What they do know is that these songs do not remain constant throughout the season. The males listen to each other and adjust their songs over the course of the mating season and throughout the years. New songs form gradually, and while they may contain themes from previous songs, the old songs will not be repeated. Whales from different areas sing in different "dialects" that may reflect the local conditions of each population, and the unique evolution of their songs.
Whale songs became a popular cultural icon in the 1970s as albums of recorded songs were best-sellers in record stores, and the two Voyager spacecraft were launched carrying gold-plated records with recorded whale songs. Many younger folks, like myself, may have been first exposed to humpback whale songs by Star Trek IV: The Voyage Home. The popularity of humpback whale songs (and others, such as a type of Indian Ocean blue whale) created a great deal of popular support for the "Save the Whales" campaign. Proponents (and the Star Trek writers) claimed the songs implied that the whales were fellow intelligent creatures, while scientists in whaling nations have played down these notions and equated them with the mooing of a terrestrial cow.
Either way, they must be heard to be fully appreciated.