When meeting up at sea, bottlenose dolphins exchange name-like whistles
When we meet a group of strangers, one of the first things we’ll do is to introduce ourselves by name. Nicola Quick and Vincent Janik from the University of St Andrews have found that groups of bottlenose dolphins do something similar. 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 – but what is their role?
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.”
Quick and Janik also found that the dolphins don’t mimic each other’s signatures when they meet up. Justin Gregg from the Dolphin Communication Project says, “In other words, dolphins are not shouting out “Hey there Jerry” to each other, they are saying “it’s me, Tim!” He adds, “We really have no idea when or why they use these whistles. This study has uncovered a brand new function for the signature whistle, which makes it rather exciting. They appear to be identifying themselves to social partners after a prolonged separation.”
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. Quick and Janik have four possible explanations for this odd pattern.
First, it’s possible that the spokes-dolphin is the leader of the group. However, these animals don’t live in a particularly hierarchical society, and there’s no good evidence for the existence of dolphin leaders. Second, dolphins might not be very choosy about who they associate with, so they don’t need to know who they’re hanging out with. Again, this seems unlikely, since we know that bottlenose dolphins do have preferred companions. Third, the dolphins might already know who’s part of which group, so they only need to hear an individual signature to remember all the others.
Janik favours the fourth option: “it’s very specific animals that are interested in joining up”. As he says, “Just like in a group of people, not everyone wants to join up with others.”
“It would be of great interest to know whether these groups join and split from each other numerous times per day or even per hour, or if they encounter one another only rarely,” says Laela Sayigh, who studies dolphin communication at the Woods Hole Oceanographic Institution. “[That] would help to differentiate among the possible interpretations.”
That’s what Janik plans to do next. He also wants to try some playback experiments – the cornerstone of animal communication research – to see if he can provoke a specific response by playing a chosen signature whistle. He also wants to see if the dolphins ever use their signature whistles to call to others who they haven’t seen in a while.
More, including an interview with one of the researchers, at the link.
Link to the full study here.
