Humpback whales are well known for their songs

Only a few hundred years ago the bays and inlets of the world were alive with the slow, restful breathing of whales and the songs whales make to communicate.

The word "song" is used in particular to describe the pattern of regular and predictable sounds made by some species of whales (notably the humpback) in a way that is reminiscent of human singing. The mechanisms used to produce sound vary from one family of cetaceans to another. Marine mammals, such as whales, dolphins, and porpoises, are much more dependent on sound for communication and sensation than land mammals are, as other senses are of limited effectiveness in water. Sight is limited for marine mammals because of the way water absorbs light. Smell is also limited, as molecules diffuse more slowly in water than air, which makes smelling less effective. In addition, the speed of sound in water is roughly four times that in the atmosphere at sea level. Because sea-mammals are so dependent on hearing to communicate and feed, environmentalists and cetologists are concerned that they are being harmed by the increased ambient noise in the world's oceans caused by ships and marine seismic surveys.

Bermuda has a small place in history when local Frank Watlington made some of the first recordings of humpback whales. Mr Watlington was an electronics specialist responsible for recording and identifying underwater sounds using hydrophones. In the 1950s and 1960s local Mr Frank Watlington was stationed at the U.S Government's Naval Underwater Systems Centre sonar listening base here in Bermuda. His job was to monitor underwater sounds for the tell-tale signs of Soviet submarines. Each spring unidentified sounds were recorded by the sonar devices, much to everyone's bafflement. It was Frank Watlington who solved the mystery, identifying the sounds as humpbacks and recording the songs. His recordings, some from as early as 1952, drew the attention of scientists including Dr Roger Payne and set in motion a series of studies of humpbacks and how they communicate. The recordings of Frank Watlington and Dr Roger Payne were included as a freebie in National Geographic and millions of readers were treated to 'Songs of the Humpback Whale', the 1979 sound sheet that made millions of readers put down their magazines and listen.

Topics covered;

• Production of sound

• Toothed whale sound production

• Baleen whale sound production

• Purpose of whale-created sounds

• The song of the Humpback Whale

• Other whale sounds

Production of sound

Toothed whale sound production

Baleen whale sound production

Purpose of whale-created sounds

While the complex and haunting sounds of the Humpback Whale (and some Blue
Whales) are believed to be primarily used in sexual selection (see section below), the simpler sounds of other whales have a year-round use. While toothed dolphins (including the Orca) are capable of using echolocation (essentially the emission of ultra-sonic beams of sound waves) to detect the size and nature of objects very precisely, baleen whales do not have this capability. Further, unlike some fish such as sharks, a whale's sense of smell is not highly developed. Thus given the poor visibility of aquatic environments and the fact that sound travels so well in water, human-audible sounds play a role in such whales' navigation. For instance, the depth of water or the existence of a large obstruction ahead may be detected by loud noises made by baleen whales.

The song of the Humpback Whale

Two groups of whales, the Humpback Whale and the subspecies of Blue Whale found in the Indian Ocean, are known to produce the repetitious sounds at varying frequencies known as whale song. Marine biologist Philip Clapham describes the song as "probably the most complex [songs] in the animal kingdom" (Clapham, 1996).

Male Humpback Whales perform these vocalizations only during the mating season, and so it is surmised the purpose of songs is to aid sexual selection. Whether the songs are a competitive behaviour between males seeking the same mate, a means of defining territory or a "flirting"
behaviour from a male to a female is not known and the subject of on-going research.

Interest in whale song was aroused by researchers Roger Payne and Scott McVay, who analysed the songs in 1971. The songs follow a distinct hierarchical structure. The base units of the song (sometimes loosely called the "notes") are single uninterrupted emissions of sound that last up to a few seconds. These sounds vary in frequency from 20 Hz to 10 kHz (the typical human range of hearing is 20 Hz to 20 kHz). The units may be frequency modulated (i.e., the pitch of the sound may go up, down, or stay the same during the note) or amplitude modulated (get louder or quieter).

A collection of four or six units is known as a sub-phrase, lasting perhaps ten seconds. A collection of two sub-phrases is a phrase. A whale will typically repeat the same phrase over and over for two to four minutes. This is known as a theme. A collection of themes is known as a song. The whale will repeat the same song, which last up to 30 or so minutes, over and over again over the course of hours or even days. This "Russian doll" hierarchy of sounds has captured the imagination of scientists.

All the whales in an area sing virtually the same song at any point in time and the song is constantly and slowly evolving over time. For example, over the course of a month a particular unit that started as an "upsweep"
(increasing in frequency) may slowly flatten to become a constant note.
Another unit may get steadily louder. The pace of evolution of a whale's song also changes-some years the song may change quite rapidly, whereas in other years little variation may be recorded.

Whales occupying the same geographical areas (which can be as large as entire ocean basins) tend to sing similar songs, with only slight variations. Whales from non-overlapping regions sing entirely different songs.

As the song evolves it appears that old patterns are not revisited. An analysis of 19 years of whale songs found that while general patterns in song could be spotted, the same combinations never recurred.

Humpback Whales may also make stand-alone sounds that do not form part of a song, particularly during courtship rituals. Finally, Humpbacks make a third class of sound called the feeding call. This is a long sound (5 to 10 s
duration) of near constant frequency. Humpbacks generally feed co-operatively by gathering in groups, swimming underneath shoals of fish and all lunging up vertically through the fish and out of the water together. Prior to these lunges, whales make their feeding call. The exact purpose of the call is not known, but research suggests that fish do know what it means. When the sound was played back to them, a group of herring responded to the sound by moving away from the call, even though no whale was present.
We need a section on "why to humpback whales sing?"

Humpback whales produce a wide array of sounds, including the highest and lowest frequencies humans can hear.

Only the males sing and in each region of the world's humpbacks has its own song. This regional song changes over time, evolving and transforming year to year.

But why, and how do the whales sing?

Other whale sounds

Most baleen whales make sounds at about 15-20 hertz. However, marine biologists at the Woods Hole Oceanographic Institution reported in the New Scientist in December 2004 that they had been tracking a whale in the North Pacific for 12 years that was "singing" at 52 Hz. The scientists are currently unable to explain this dramatic difference from the norm; however, they are sure the whale is a baleen and extremely unlikely to be a new species, suggesting that currently known species may have a wider vocal range than previously thought.

Most other whales and dolphins produce sounds of varying degrees of complexity. Of particular interest is the Beluga (the "sea canary") which produces an immense variety of whistles, clicks and pulses.