Jennifer Viegas,Discovery News
March 10, 2008 -- "Hack hack hack pyow hack hack" might not mean much to human ears, but to a putty-nosed monkey it means, "I'm adult male X; I have just seen an eagle; I will now move away," according to a new study showing that primates can combine individual calls to express different meanings.
While such syntax-like behavior has been described in other species, such as whales and dolphins, the new findings are the first to clearly demonstrate the skill in a non-human primate.
"What our research shows is that individual calls do not carry any specific meanings, but different call sequences do," co-author Klaus Zuberbuhler told Discovery News.
"So, for example, a series of hacks almost certainly indicates the presence of a crowned eagle, whereas a series of hacks preceded by 1 to 2 pyows reliably indicates that the caller is about to start traveling away," added Zuberbuhler, who is a researcher in the School of Psychology at the University of St. Andrews in Scotland.
For the study, published in this week's Current Biology, Zuberbuhler and colleague Kate Arnold focused on alarm calls emitted by free-ranging male putty-noses at Gashaka Gumti National Park, Nigeria. These monkeys live in groups with one male, six to nine females and their offspring.
The scientists first observed that when males emitted a mostly "pyow"-based call series, a leopard was around. "Hack" sounds followed by "pyows," in turn, were linked to the presence of an eagle. The males also assembled these two alarm calls into unique "pyow-hack" sequences.
Using a GPS unit, the researchers tracked how females would move in response to hearing certain recorded calls. As predicted, the females moved whenever the sounds indicated the caller was traveling and that an eagle was present.
Since the monkeys usually just hide up in the forest canopy in the presence of a leopard, both the calling male and the listening females stayed relatively put in response to leopard-linked calls.
The researchers next created their own pyow-hack call combinations, to test their predictions about how the females would respond upon hearing them. Their predictions proved correct.
Finally, the scientists played alarm calls made by a strange male to the females, who appeared to ignore what they heard. Since one male putty-nosed monkey sounds very much like the next, this last experiment suggests the vocalization sequences contain information about the identity of the caller, in addition to what he saw and his planned reaction.
"If females responded by approaching every stranger male producing pyow-hack sequences, then they would simply be unable to have a normal social life," explained Zuberbuhler.
He and Arnold have identified call combinations in a number of other primate species, including gibbons, Campbell's monkeys and olive colobus monkeys, suggesting that "the phenomenon is much more widespread," he said.
The researchers believe non-human primates create call sequences to increase the meaning mileage of their small vocal repertoires, which are restricted due to their lack of good tongue control.
Marc Hauser, director of the Cognitive Evolution Lab and co-director of the Mind, Brain & Behavior Initiative at Harvard University, told Discovery News that the new research "is a beautiful set of studies," but "how similar or different [monkey call combinations] are to the combinations of words in language remains, however, unclear."
Asif Ghazanfar, assistant professor of psychology at Princeton University, told Discovery News that he was also impressed by the new research. For a follow-up experiment, he suggested trying to trip up the female monkey listeners.
"One experiment that would've been nice to try is to reverse the order: do playbacks of hack-pyow sequences to see if the temporal order matters to the monkeys, as temporal order can change meaning in human communication," Ghazanfar said.
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Source: Discovery news
While such syntax-like behavior has been described in other species, such as whales and dolphins, the new findings are the first to clearly demonstrate the skill in a non-human primate.
"What our research shows is that individual calls do not carry any specific meanings, but different call sequences do," co-author Klaus Zuberbuhler told Discovery News.
"So, for example, a series of hacks almost certainly indicates the presence of a crowned eagle, whereas a series of hacks preceded by 1 to 2 pyows reliably indicates that the caller is about to start traveling away," added Zuberbuhler, who is a researcher in the School of Psychology at the University of St. Andrews in Scotland.
For the study, published in this week's Current Biology, Zuberbuhler and colleague Kate Arnold focused on alarm calls emitted by free-ranging male putty-noses at Gashaka Gumti National Park, Nigeria. These monkeys live in groups with one male, six to nine females and their offspring.
The scientists first observed that when males emitted a mostly "pyow"-based call series, a leopard was around. "Hack" sounds followed by "pyows," in turn, were linked to the presence of an eagle. The males also assembled these two alarm calls into unique "pyow-hack" sequences.
Using a GPS unit, the researchers tracked how females would move in response to hearing certain recorded calls. As predicted, the females moved whenever the sounds indicated the caller was traveling and that an eagle was present.
Since the monkeys usually just hide up in the forest canopy in the presence of a leopard, both the calling male and the listening females stayed relatively put in response to leopard-linked calls.
The researchers next created their own pyow-hack call combinations, to test their predictions about how the females would respond upon hearing them. Their predictions proved correct.
Finally, the scientists played alarm calls made by a strange male to the females, who appeared to ignore what they heard. Since one male putty-nosed monkey sounds very much like the next, this last experiment suggests the vocalization sequences contain information about the identity of the caller, in addition to what he saw and his planned reaction.
"If females responded by approaching every stranger male producing pyow-hack sequences, then they would simply be unable to have a normal social life," explained Zuberbuhler.
He and Arnold have identified call combinations in a number of other primate species, including gibbons, Campbell's monkeys and olive colobus monkeys, suggesting that "the phenomenon is much more widespread," he said.
The researchers believe non-human primates create call sequences to increase the meaning mileage of their small vocal repertoires, which are restricted due to their lack of good tongue control.
Marc Hauser, director of the Cognitive Evolution Lab and co-director of the Mind, Brain & Behavior Initiative at Harvard University, told Discovery News that the new research "is a beautiful set of studies," but "how similar or different [monkey call combinations] are to the combinations of words in language remains, however, unclear."
Asif Ghazanfar, assistant professor of psychology at Princeton University, told Discovery News that he was also impressed by the new research. For a follow-up experiment, he suggested trying to trip up the female monkey listeners.
"One experiment that would've been nice to try is to reverse the order: do playbacks of hack-pyow sequences to see if the temporal order matters to the monkeys, as temporal order can change meaning in human communication," Ghazanfar said.
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Source: Discovery news
