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A Whale Expert is Called in to Decipher Odd Elephant CallsWHOI biologist's expertise in marine mammal communication proves useful in studies of other large (albeit terrestrial) mammals |
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| Enlarge ImageCalimero, a male African elephant in a zoo, learned to imitate the sounds made by female Asian elephants he was housed with. His ability to learn through imitating sounds, called “vocal learning,” is rare among animals and was previously only known in birds, bats, and marine mammals. (Photo by Angela S. Stoeger-Horwath, University of Vienna) |
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| Enlarge ImageWHOI biologist Stephanie Watwood studies the sounds whales make to communicate and forage under water. She was asked to apply her expertise to decipher the calls of elephants, which use similar types of sound to communicate. On the screen is the wave form (amplitudes of the call vs. time) of a "chirp" sound made by an Asian elephant. (Photo by Tom Kleindinst, WHOI) |
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Stephanie Watwood had no reason to expect that two elephants would
cross her path. Nor did she anticipate their surprising vocal
impersonations.
Not that Watwood was unfamiliar with leviathan-sized mammals. As a
biologist at Woods Hole Oceanographic Institution, she studies whale
and dolphin communication. Marine mammals are known to forage for prey,
broadcast their identity, and establish social bonds using sounds that are
transmitted efficiently through water. They can even learn to
make new sounds by imitating what they hear—a process known as “vocal
learning.”
“We know that humpback whales, for example, sing during the breeding
season,” Watwood said. “They learn songs from each other, and the songs
change. All the whales within one area will imitate one another and
help spread the change in songs from year to year.”
“It’s an ability that’s not very common among animals,” she said.
“Songbirds and parrots have this ability, and bats, cetaceans, and
pinnipeds (such as seals and walruses), and that’s pretty much it.”
At least until the elephants showed up in her lab. It happened this way.
Strange sounds
Joyce H. Poole, a researcher at the Amboseli Trust for Elephants in
Kenya, was studying vocal behavior in African elephants, Watwood said.
“She had friends who were running an orphanage for elephants, and they
had heard this female elephant, Mlaika, making strange sounds, so Joyce
went to check it out.
“When Joyce was sitting near the elephant compound, she could hear
trucks in the far distance,” Watwood said. “And then, when she was
sitting there listening to Mlaika, instantly she said, ‘Wow, she sounds
like those trucks I’m hearing!’ ”
Meanwhile, another elephant communication researcher, Angela S.
Stoeger-Horwath of the University of Vienna, had discovered a male
African elephant named Calimero living in a zoo with female Asian
elephants—a different genus and species. He didn’t make any normal male
African elephant sounds, but mimicked the chirping calls of his female
roommates.
Stoeger-Horwath shared her findings with Poole, and they agreed: These
elephants seemed to have learned to imitate unusual sounds. Then they
remembered hearing a lecture by Peter Tyack, a WHOI biologist and an
expert on vocal learning in marine mammals. That’s how two elephant
researchers in Europe and Africa ended up in contact with Watwood in
Woods Hole.
“They were looking for someone who would believe that their elephants made funny sounds,” Watwood said.
Pachyderm mimicry
The two elephant researchers sent Tyack numerical data on the
elephants’ calls. Watwood, an expert in analyzing similar data from
marine mammal sounds, compared the frequencies and duration of Mlaika’s
and Calimero’s calls with the sounds of the trucks and the Asian elephant
females. The work of Poole, Tyack, Stoeger-Horwath, and Watwood
demonstrated for the first time that elephants, too, have the ability
to learn and imitate vocal sounds.
Like whales and dolphins, elephants have strong social structures and
they use low-frequency sound to communicate over wide expanses. “People
have speculated that elephants communicate over many kilometers,”
Watwood said, “and one study showed they can recognize who produced the
calls, over considerable distance from at least a kilometer away.”
“Elephants do make those loud trumpet calls, which is what they show on
the movies all the time,” Watwood said, “but most of the sounds made by
adults are really low-frequency rumbles, below the human range of
hearing.”
The sounds that Mlaika and Calimero made did not exactly match the
trucks and the Asian elephants, Watwood said, but it was clear that
they were trying hard to mimic those sounds to the best of their
abilities.
“Truck sounds are very low frequencies, well within the range of sounds
that elephants produce,” Watwood said. “The truck sound that Mlaika
imitated was a lo-o-o-o-o-ong sound—much longer calls than she normally
would make.”
“Calimero is much bigger than an Asian elephant female and so had a
lower voice; he called at a lower frequency than females would,”
Watwood said. “But he put more of his vocal energy in frequencies that
were much higher than a typical elephant of his size would make. He was
doing his best to sound like a smaller elephant.”
— Kate Madin
This research was funded by Woods Hole Oceanographic Institution.
Posted: July 28, 2005 [top] |
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