An article titled “Vocal copying of individually distinctive signature whistles in bottlenose dolphins” is in the news this week. This is the latest in a series of studies from researchers at the University of St Andrews looking at how dolphins use “signature” whistles. Signature whistles are unique vocalizations that each dolphin develops at a young age that (sometimes) remains stable throughout their lives. It’s easy for humans, and presumably dolphins too, to hear the difference between dolphins’ signature whistles, which makes them useful for recognizing individual animals.
This study found that dolphins occasionally copy the signature whistles of their close associates (e.g., mothers and calves, male alliance partners), which is evidence that dolphins are using these whistles for friendly purposes, as opposed to territorial defense or aggression (which is often how bird species use copied sounds). The dolphins also appear to purposefully introduce very subtle changes in the copied whistles, which suggests they are not trying to deceive each other by pretending to be someone else.
It’s rare that animal communication results in animals having labels for objects in their environment – in this case it’s possible that the signature whistle is a kind of label that refers to individual dolphins. The most common examples of referential communication in the animal kingdom are alarm and food calls, which are found in diverse species (e.g., monkeys, rodents, chickens). Signature whistles are unique insofar as they are not used to refer to threats or food, but appear to refer to themselves, and possibly other dolphins. While we know from experiments that dolphins are able to learn both visual and acoustic labels for objects and concepts (something birds, primates, dogs and other animals can do as well), this is one of those rare cases where an animal might have a label for something in its natural communication system.
Unfortunately, this study was not able to tell us if dolphins copy the signature whistles of other dolphins in order to specifically refer to and/or get the attention of that individual or not. They might simply be copying the whistles/sounds which they hear most often in their environment and reproduce them as a general contact or distress call in times of trouble, which would explain why they copy the whistles of their close associates. It’s worth noting that the dolphins in this study didn’t actually copy each others’ whistles all that much – only 12 of the 121 individual dolphins in the capture-release scenario copied whistles at all, and then at a rate of only 0.18 copies per minute, which suggests that whistle copying is a rare-ish event. Although the media is keen to suggest that dolphins call each other by name, this is a bit of an oversimplification or exaggeration insofar as we still don’t know how label-like or referential these whistles really are, of if the dolphins producing the whistles of their associates truly intend to refer to or label that animal or not. As the lead author of this study, Stephanie L. King, noted in an interview with Wired: “We still need to show that experimentally, but that’s why it’s quite exciting.” Indeed! Hopefully the St. Andrew’s group will get to the bottom of this in future studies.
King SL, Sayigh LS, Wells RS, Fellner W, & Janik VM (2013). Vocal copying of individually distinctive signature whistles in bottlenose dolphins. Proceedings. Biological sciences / The Royal Society, 280 (1757) PMID: 23427174
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