Marine mammals produce sounds that are associated with reproduction. These sounds can function in two ways. First, males can produce vocalizations to compete with other males for access to a female. Second, females can compare males based on the vocalizations they produce. In both cases, the males produce the vocalizations associated with reproduction. The best known example of marine mammals using sound as a reproductive advertisement comes from the humpback whale.

Humpback whales are known for their songs. These songs, most often heard on their breeding grounds, are associated with courtship displays. Photo ©Tsuneo Nakamura (Go to larger version)

Humpback males produce a series of vocalizations that collectively form a song. These songs can be heard by whales up to 10 km (about 6 miles) away. Humpback songs are heard most often in tropical waters during the breeding season. Songs of the humpback are also heard in cooler waters as the whales travel to and from breeding grounds, but these songs are not heard nearly as often as those on the breeding grounds. Humpback songs are complex in structure and long in duration. Whales have been known to sing the same song for hours and hours.

A typical humpback song is made up of 3 to 9 themes sung in a particular order that creates a series. It takes approximately 10-15 minutes for a whale to sing the entire series before returning to the beginning. Each theme is made up of its own phrases that are repeated until the theme is changed. The phrases are composed of repeated parts or variables. For example, suppose a humpback song is composed of 5 themes labeled 1 through 5. Each theme is made up of phrases labeled A, B, C, D, and E. Phrases A, B, C, D, and E are composed of variables a, b, c, d, e, f, and g. Putting this all together, you get a song that looks like this in structure.

Songs from different whales on the same breeding area have very similar themes. However, these themes change on a monthly and yearly basis. It is not completely known how or why the song themes change so often, but the changes do not seem to be associated with a change in the function of the song or its meaning. It is thought that one function of a humpback song is to establish hierarchy among males on the breeding grounds. Songs appear to maintain spacing between singing males. Aggressive interactions have also been observed between singing males and non-singing males. A second function of the song of the humpback is to provide females with information for choosing between competing males.