Dolphins say hello with signature tunes

Wild dolphins use specific melodies called signature whistles to introduce themselves when they come across new groups of dolphins, researchers have discovered.

They say the tuneful exchanges are an important part of a greeting sequence that allows dolphins to recognize each other in the wild.

Dr. Vincent Janik from the University of St. Andrews led the study. He explained:

These signature whistles are special, because they contain the dolphin’s identity in the modulation pattern, or tune if you like, which the dolphin invents.

Signature whistles were first discovered in the 1960s. Janik said:

Researchers had already brought up the idea that they’re whistles that dolphins use to identify themselves.

Scientists also noticed that captive dolphins use these whistles when apart from the rest of the group. But no-one had actually demonstrated their use in the wild – until now. Janik said:

People thought that dolphins use signature whistles to update others about where they are. After all, they live in a 3D world, with no real landmarks. Beyond that, we didn’t know much about what they use signature whistles for.

Janik and his colleague, Dr. Nicola Quick – also from the University of St. Andrews – figured that if these intelligent creatures use signature whistles to tell others who they are, they should exchange them when groups meet. So, they decided to analyse when and how a 200-strong dolphin population around the east coast of Scotland uses these whistles.

Janik and Quick expected every individual in the pod to introduce themselves whenever they came across a new group. But – much to their surprise – they didn’t find that at all. Instead, it seems that it’s enough for just one dolphin to identify itself to elicit a reply from a member of the other group. Janik said:

It’s like a greeting ceremony between a couple of individuals in two different groups. These individuals have a close interaction, but the others are more passive.

Dolphins have a huge repertoire of whistles, which make it hard to work out which one was the signature. Not just that, but the creatures whistle with a special structure in their foreheads. This means they don’t open their mouths. So once Janik and Quick had identified which whistle could be labelled a signature whistle, they then had the added problem of working out which dolphin it came from. Janik explained:

We used four sensors and then worked out the time of arrival of the whistle to say which dolphin made the tune.

They also noticed that when individuals meet a new group, they repeatedly replay their signature tune. Janik reports in Proceedings of the Royal Society B that this almost certainly helps with correct identification.

Dolphin social structure is much like ours; they have a fission-fusion system, in which individuals in each group change all the time. So if only one individual from a fairly fluid group introduces themselves, how does the group know who the others are?

Janik explained that it’s likely the dolphins also use active sonar to identify each other. But right now, they’re not sure how much. He said:

We know their echolocation is incredibly finely tuned: they can pick up an object which is just seven centimetres across from 100 metres away. So they could be using this to identify features in others.

He says the next step will be to see how bigger populations of dolphins which live in larger area of the ocean use these signature whistles.

To complete the picture, it would also be important to look into how echolocation is used to perceive who’s around them.

Bottom line: New research suggests that wild dolphins use specific melodies, called signature whistles, to greet and recognize other dolphins.

March 7, 2012

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