The vocalizations of humpback whales, between secrets and mysteries

Humpback whale vocalizations are performed only by males and only during the mating season, suggesting that the purpose of the songs is to aid natural selection

by Lorenzo Ciotti
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The vocalizations of humpback whales, between secrets and mysteries

Humpback whales are found in waters all over the world, with the exception of some areas near the equator, in the high Arctic and in some enclosed seas. The northernmost point where they have been reported is at 81° north along the northern coast of Franz Josef Land.

They are generally coastal creatures and tend to congregate in waters above the continental shelf. Their winter breeding grounds are found around the equator, while their summer feeding grounds are located in colder waters, even near the polar caps.

In the North Atlantic there are two distinct wintering populations, one in the West Indies, between Cuba and northern Venezuela, and the other in Cape Verde and northwest African waters. During the summer, West Indian humpback whales congregate off New England, eastern Canada, and western Greenland, while the Cape Verde population congregates around Iceland and Norway.

Humpback whale vocalizations are performed only by males and only during the mating season, suggesting that the purpose of the songs is to aid natural selection. Whether songs are competitive behavior between males following the same potential mate, a system for defining territory or a male-to-female courtship technique is not known and is still being studied.

Interest in whale song was sparked by researchers Roger Payne and Scott McVay, who analyzed the songs in 1971. The songs follow a distinct, hierarchical structure. The basic units of singing are unitary and uninterrupted emissions of sounds that persist up to a few seconds.

These sounds range in frequency from 20Hz to 10kHz. The units can be frequency modulated or even amplitude modulated. A collection of four or five units is known as a sub-sentence, lasting perhaps ten seconds. A collection of the two sub-sentences constitutes a sentence.

Also, each whale song evolves slowly over time. For example, over the course of a month a particular unit that started out as an upward-grading tonality. Humpbacks can also make isolated sounds that are not part of a song, particularly during courtship rituals.

Humpback whales also produce a third class of sounds called meal calls. This is a sustained sound of five to ten seconds, with an almost constant frequency. Humpback whales generally feed cooperatively by grouping, swimming under schools of fish and cutting vertically through the fish and out of the water simultaneously.

Before these movements the whales make their feeding calls. The exact purpose of the calls is not known, but research suggests that fish recognize them.