Posted by "CavalierZee"
Courtesy Of "Discover Magazine"
Nicola Quick and Vincent Janik from the University of St Andrews have found that groups of Bottlenose Dolphins, When they meet one another in the wild, they exchange “signature whistles”. These whistles are unique to each individual, and they’re strikingly similar to human names. And it seems that they’re a standard part of a dolphin’s meet-and-greet etiquette.
Signature whistles were first discovered by Melba and David Caldwell in the 1960s, but we still know relatively little about how they’re used. We know that bottlenose dolphins develop their signatures when they’re a few months old, possibly modelling them on those of their mothers. They can go unchanged for decades, although males will sometimes change their whistles to resemble that of a new ally.
The signature whistles seem to act like badges of identity. One dolphin can learn information about another by listening to its whistle. But they’re not entirely like human names. For a start, they’re invented, rather than bestowed. They also convey more than just identity – they reveal the caller’s motivation or mood. “It’s a bit like in human language, where you can hear if a person sounds happy or sad, not in the choice of words they make, but in subtle acoustic features in their speech,” explains Janik.
In captivity, a dolphin will emit its signature whistle if separated from the rest of its group. This suggests that the whistles could act as contact calls, which they continuously make to stay in touch. Dolphins can even mimic each other’s signatures, perhaps just as we call each other by name. But in the wild, no one knows exactly how the whistles are used. They’re clearly common part of dolphin life – half of all the calls recorded from wild dolphins are signature whistles.
To investigate the role of signature whistles, scientists needed to work with free-swimming dolphins. That’s easier said than done. In the past, people have captured wild dolphins, recorded their calls, identified the signature whistles, and released the animals. How do you parse out a specific signal from the underwater cacophony of a fast-moving dolphin pod?
Janik found a way in Florida, while working with Randy Wells. Together, they noticed that the signature whistles have a distinctive rhythm. “The whistles occurring within 1 to 10 seconds of each other,” he says, “and you can use this pattern to identify signature whistles in free-swimming animals. Using the methods he perfected in Florida, Janik returned to Scotland, to work with a group of dolphins he had been studying since 1994.
Quick and Janik recorded the calls of swimming dolphin pods using underwater microphones. From 11 such recordings, they worked out that dolphin groups use their signature whistles in greeting rituals, when two groups meet and join. Only 10 per cent of such unions happen without any signature whistles. And the dolphins use their signatures nine times more often during these interactions than during normal social contact.
The signature whistles clearly aren’t contact calls, because dolphins hardly ever use them within their own groups. Mothers and calves, for example, didn’t exchange signature whistles when travelling together. And they’re not confrontational claims over territory, because bottlenose dolphins don’t have territories.
Instead, Janik thinks that dolphins use the whistles to identify themselves, and to negotiate a new encounter. The human equivalent would be saying, “My name is Ed. I come in peace.” Janik explains, “You often see ritualised behaviour sequences when animals meet. We say hello or shake hands. That doesn’t have much meaning – it’s just what you do when you meet someone else.”
But the recordings threw up a big surprise: not every dolphin exchanges its signature whistle when two groups meet up. Usually, just one member of each group does so.
Reference: Quick & Janik. 2011. Bottlenose dolphins exchange signature whistles when meeting at sea. Proc Roy Soc B. http://dx.doi.org/doi:10.1098/rspb.2011.2537
Photos by NASA and BBMI explorer
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