Function of Signature Whistles

Signature whistles are thought to function as markers for identity of individual dolphins. As was mentioned in the section on structure of signature whistles, the whistle itself is composed of both the stable signature portion as well as a variable section. The variable section is thought to convey information related to the dolphin’s environment.

As soon as the calf is born, it begins to develop its own unique signature whistle. Mother and calf pairs use signature whistles to keep in contact with each other as the calf begins to venture away from its mother. Observations have revealed that a greater number of signature whistles occur just before the mother-calf pairs reunite (Catton 1995).

Interestingly, males tend to develop signature whistles similar to that of their mother’s whistle, while females tend to create new ones. It is thought that the unique signature whistle of females is needed so that when mature females return to the female band, their whistle is not confused with that of their mother’s whistle (Catton 1995).

Sex differences in animal vocalizations are widespread. Previous studies have assigned categories to sex-specific vocal differences. Such categories include vocalizations produced by only one sex (for example mating calls), as well as vocalizations shared by both sexes, but used for different purposes (Sayigh et al. 1995).

This sex difference with respect to signature whistles is accounted for by the tendency of females to develop close bonds with each other. On the other hand, males are able to retain a whistle similar to that of their mother’s because they will not return to the female band which there mother is associated with. If a female dolphin had developed a signature whistle similar to that of her mother, upon returning to the band confusion would develop, as two dolphins would possess the same identifying feature in their whistle. Therefore, a selective pressure exists for females to develop unique signature whistles (Sayigh, Tyack, Wells, Scott, Irvine 1995).

Selective pressures exist mainly on the female bottlenose dolphins. Females benefit from having distinct signature whistles so that they can differentiate their own offspring from those of other parents (Sayigh, Tyack, Wells, Solows, Scot and Irvine 1998).

It was found in a study conducted that 100% of females produced highly distinctive signature whistles from that of their mothers, while 100% of males produced highly similar whistles to that of their mothers. The researchers noted that the sex difference in signature whistle vocalizations is unique to bottlenose dolphins, and has not been observed in terrestrial males (Sayigh 1995).

Research has also shown evidence that bottlenose dolphins are able to mimic other dolphin’s signature whistles (Tyack 1997). Catton (1995) reported that females learn the whistles of other females so that they can call them by name. On the other hand, males may use the signature whistles of their cohorts to avoid aggressive encounters from other groups of males. If the male is able to give the impression that he is with a large group of males, then he may be able to avoid potential conflicts.

Return to Index