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Monkey see, monkey warn. A blue monkey looks out for its pals.

Florian Möllers/

Monkeys Give a Hoot

"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."

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