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By Virginia MorellScienceNOW • Tuesday February 26, 2013 3:25 PM

Every bottlenose dolphin has its own whistle, a high-pitched, warbly “eeee” that tells the other
dolphins that a particular individual is present. Dolphins are excellent vocal mimics, too, able to
copy even quirky computer-generated sounds. So, scientists have wondered if dolphins can copy each
other’s signature whistles.

“It’s a wonderful study, really solid,” says Peter Tyack, a marine mammal biologist at the
University of St. Andrews in Britain who was not involved in this project. “Having the ability to
learn another individual’s name is . . . not what most animals do. Monkeys have food calls and
calls that identify predators, but these are inherited, not learned sounds.” The new work “opens
the door to understanding the importance of naming.”

Scientists discovered the dolphins’ namelike whistles almost 50 years ago. Since then,
researchers have shown that infant dolphins learn their individual whistles from their mothers. A
1986 paper by Tyack did show that a pair of captive male dolphins imitated each others’ whistles,
and in 2000, Vincent Janik, who is also at St. Andrews, succeeded in recording matching calls among
10 wild dolphins.

“But without more animals, you couldn’t draw a conclusion about what was going on,” says
Richard Connor, a cetacean biologist at the University of Massachusetts Dartmouth. Why, after all,
would the dolphins need to copy another dolphin’s whistle?

Unraveling dolphin calls is not easy; they produce their sounds underwater, often in murky
conditions, which makes it difficult for scientists to identify which animal is emitting which
call. To get around this problem, Stephanie King, a marine biologist also at the University of St.
Andrews, and her colleagues analyzed the acoustic recordings of dolphin signature whistles that
scientists with the Sarasota Dolphin Research Program made of more than 250 wild bottlenose
dolphins briefly captured between 1984 and 2009 in Sarasota Bay, Fla. She also recorded the
signature whistles of four captive dolphins and made detailed observations of their behaviors while
whistling.

The scientists with the Sarasota program had captured pairs and groups of dolphins and held
them separately in nets for 108 minutes on average. During this time, the marine mammals could not
see each other, but they could hear each other, and they whistled at a high rate, sometimes giving
more than five calls per minute. In the wild, too, dolphins use their signature whistle at a high
rate, King notes; it is one of the most common sounds they make.

King and her colleagues compared the spectrograms or visual representations of the wild
dolphins’ whistles and one pair of the captive dolphins, looking for evidence that the dolphin
pairs copied each other’s sound. They identified whistle-matching in 10 of the 179 dolphins
recorded in the Sarasota study, and one of the captive pairs. The males in two pairs had copied
each other’s whistles, as had eight mother-and-calf pairs, the team reported last week in the
Proceedings of the Royal Society B. The dolphins did this quickly, too, repeating the other’s
whistle within one second of hearing it. Those dolphins who copied whistles also only imitated the
call of their closest social partner.

“It means they were calling a specific individual,” King says. “They produce the copies when
they are separated, which we think shows that they want to reunite with a particular individual.”
It’s what we do if we get separated from our friends at a fair or the mall, she adds. “You don’t
call out your name; you call the name of your friend. That’s how you get back together.”

Dolphins don’t copy just anybody’s signature whistle; they are very selective in how they use
this talent, using it solely to maintain bonds between mother and calf and between allied males,
King says. The scientists recorded one pair of males twice, once at the beginning of the project
and then 12 years later. Even after all that time, each dolphin “copied the fine details of the
other’s whistle,” King says, an indication of the pair’s especially tight bond.

“There’s been some evidence before that dolphins are imitating each other’s whistles,” Connor
says. “But this is the first really convincing paper. It’s very exciting.”

“It is fabulous,” adds Karl Berg, an ornithologist at the University of California, Berkeley,
who specializes in parrot calls. He notes that dolphin results are “strikingly similar to recent
work on parrots,” which also imitate each other’s vocalizations, sometimes as a way of negotiating
foraging or roosting decisions.

King found no evidence that the dolphins used their whistle-copying to be aggressive or to
deceive other dolphins, as some have hypothesized. The dolphins that imitated another dolphin’s
whistle did so only to reestablish contact with a specific individual. But in some cases, the
dolphins added parts of their own signature whistle to the copy of their friend’s, which suggests
that they may also be including additional information - which would not surprise either Berg or
Connor. “The ability to imitate social companions can lead to more complicated exchanges of
information,” as well as disagreements, Berg says.

Connor notes that King’s study focused on the signature whistles of captured dolphins that
were separated from their social partners, and so may not be representative of how wild dolphins
more typically use their calls. “How do they use these calls in the wild? Can they add ‘help’ to
someone’s signature whistle?” he asks, noting that male dolphins come to each other’s aid when
battling over females. “Can they add sounds that say they like or dislike someone? If you can say
somebody’s name, there’s no reason why you can’t talk behind his back.” King is already tackling
these questions with a new round of experiments.