Dolphins are like humans in many ways: They're part of complex social networks and, just as in people, a dolphin's brain is big, relative to the size of its body. But there's something else, too — a study published Monday shows these acrobats of the sea use name-like whistles to identify and communicate with each other.
"In the underwater environment, animals use their own signature whistles to broadcast their identity and say, 'I'm here, I'm here,' " says Stephanie King, a marine biologist at University of St. Andrews and author of the study.
In the first few months of its life, every bottle-nosed dolphin develops its own unique whistle.
Scientists have known about these signature whistles for decades. And earlier this year, in a separate study, King and her colleagues showed that when bottle-nosed dolphins in captivity get separated from each other, they call out to their loved ones by imitating their whistles.
"They were calling the unique identity signal of a friend they wanted to reunite with," she says.
But because that study mostly involved pre-existing recordings, King couldn't tell whether the other dolphin really answered the calls. And she didn't know if this behavior happened in the wild.
To try to find out, she and a colleague recorded the identity whistles of 12 dolphins living off the east coast of Scotland. Then they modified those whistle sounds slightly so it would sound like a second dolphin was making the first dolphin's whistle sound. Then the researchers played back these modified whistles using underwater speakers.
"It was very exciting to see that every time a dolphin heard its signature whistle, it called back, sometimes multiple times," King says.
Not only did the dolphins call back, but they even swam toward the speakers that were playing the sound. It was behavior you might expect if two friends were trying to find each other in a crowd. King and her colleague have published their findings in the Proceedings of the National Academy of Sciences.
"This new study shows that when a dolphin hears an imitation or copy of its own signature whistle, it will respond immediately," says Peter Tyack another marine biologist at University of St. Andrews.
But are these whistles the dolphin version of human names? That, Tyack says, is harder to tell. "To get at the issue of naming," he says, "we have to go beyond the function of the communication to a more cognitive question."
For example, he says, does hearing another dolphin's whistle bring up in the dolphin's mind an image of that particular animal? These are obviously hard questions to answer, Tyack says, but they're well worth asking.