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http://sciencenow.sciencemag.org/cgi/content/full/2008/723/3

Monkeys Give a Hoot

By Lauren Cahoon

ScienceNOW Daily News

23 July 2008

"Watch out!" It's a simple phrase, but researchers have long debated
whether nonhuman primates use something like it. A new study indicates
that they do: Even when not threatened themselves, African blue
monkeys warn neighbors of nearby predators. However, some skeptics
maintain that the animals are acting out of fear, not concern for
others.

Blue monkeys (Cercopithecus mitis stuhlmanni) have two
predator-specific calls: the "hack," a low, gagging sound that warns
about eagles, and the "pyow," which sounds a bit like a laser gun and
warns about more general dangers on the ground, such as leopards. When
a monkey sounds a particular alarm, its neighbors know to look out for
that predator. Although listeners clearly understand the warnings,
many scientists think that hack and pyow reflect only a basic,
emotional response--a scream of fear rather than a "Hey you, look
out!"

That's not what Klaus Zuberbühler noticed in a Ugandan nature reserve.
The psychologist at the University of St. Andrews in Fife, U.K., and
colleagues played recordings of hacks and pyows from a loudspeaker
near blue monkey troops, which are usually made up of a lead male and
about 10 to 40 females and young. The recorded sounds prompted the
lead male to follow up with his own alarm call, and he typically
repeated the cry about 23 times. However, if a female or baby was
close to the loudspeaker--the "predator"--the males gave an average of
42 cries. It didn't matter how close the male was to the danger; he
sounded the red-alert alarm only when the females and young appeared
to be at risk.

"This really goes against a lot of current writing that portrays
nonhuman primates as very egoistic," says Zuberbühler, whose team
reports its findings today in Biology Letters. "What exactly goes on
in these monkeys' minds is, of course, a difficult question, but ...
the male seems to be warning them regardless of his own threat."

The debate is far from settled, however. Michael Owren, a psychologist
specializing in primate communication at Indiana University,
Bloomington, doesn't think the study proves that the monkeys are
purposefully warning others. Instead, he says, the females' proximity
to the "predator" may just make the males extra emotional.

But Gregory Radick, a science historian who writes on primate language
at the University of Leeds, U.K., finds the study's conclusions worth
considering. He notes that although the monkey could be motivated by
fear, it's still adjusting its alarm based on the threat that's posed
to others. The jury may be out for quite some time, he says. "This
kind of experiment is not easy to interpret, ... and that leaves room
for other people to throw some doubt on the experiment's meaning."