The team found that the listening dolphins responded strongly to recordings of the names of their relatives and close group members but largely ignored those of other dolphins.
Janik says the recordings were synthesized electronically to rule out the possibility that the dolphins recognized each other simply by the sound of their voices.
"It's the equivalent of a computerized voice, where you can't tell who is speaking by the voice alone," he said.
The study team says whistles that identify an individual would be especially useful to bottlenose dolphins, because they live in large groups and have complex social interactions.
"Group changes are incredibly dynamic, and you need a way of knowing exactly who's around you," Janik said. "Dolphins often prefer to spend time with particular individuals."
But living in the murky ocean makes it hard to hook up with your dolphin buddies.
"Finding each other isn't so easy in marine environments, because visibility is very poormaybe just a couple of meters," Janik said.
"Instead of looking around, they really need some other obvious and reliable system to find another animal."
The researchers suggest the dolphins use acoustic communication and signature whistles to locate and identify individual animals.
"You really have to have something more than a voice. You need something that's as different as a name," Janik said.
The ability to develop individually distinctive calls requires vocal learning, a relatively rare skill that's seen in humans, dolphins, elephants, and a few other animals including certain birds.
(Read related news: "Elephants Can Mimic Traffic, Other Noises, Study Says.")
Bottlenose dolphins are among the most versatile vocal learners and show cognitive abilities similar to those of primates.
The study team says young dolphins appear to create their own signature whistles from those of adult dolphins.
"They are listening to a lot of other whistles in the environment, then take parts of some that they've heard and put them together as a new one," Janik said.
Other researchers, however, have argued that dolphins don't have signature whistles.
In 2001 Brenda McCowan of the University of California, Davis, and Diana Reiss of the New York Aquarium in Brooklyn published a study suggesting that bottlenose dolphins don't use individual names but rather a shared contact call.
Their research was based on captive dolphins, which, Janik says, wouldn't have the same difficulties wild dolphins have with staying in touch.
"They don't live in the kind of complex environment that wild dolphins inhabit," he said. "They are in relatively small environs, in very clear water, and can see each other all the time."
Janik says that bottlenose dolphins may turn out to be just the first of various animals that use their own names.
Researchers have identified what could be signature whistles in other dolphin species, including spotted, white-sided, and dusky dolphins.
Some birds possibly also use names to communicate with each other, Janik adds.
"The one group of birds where that's possible is parrots," he said.
"Parrots have a very similar social structure to dolphins, and it seems they may also have a similar [naming] system."
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