Ever whispered behind someone's back because you really don't like them? C'mon ... you know you have. No need to feel too bad – you're not alone in your whispering ways. It turns out some tamarin monkeys do the same. Research conducted at New York City’s Central Park Zoo shows that cotton-top tamarin monkeys display 'whisper-like behaviours' in the presence of humans they don't like. 

2013 09 24 Tamarin Monkeys Whisper 01
Tamarin monkeys whispering.jpg Image caption: Psst! Obnoxious human at six o'clock! Image credit: Jasper Nance, Flickr

As a species, the cotton-top tamarin (Saguinus oedipus) is well known for its vocal accomplishments – the New World monkeys have an impressive repertoire of calls to suit different situations, from bird-like chirps and whistles to barks and high-pitched trilling. These advanced communication skills are key for a sociable species that lives in large groups and displays cooperative breeding (where only one dominant pair produces offspring and everyone else pitches in to raise them). 

“Research conducted at New York City’s Central Park Zoo shows that cotton-top tamarin monkeys display 'whisper-like behaviours' in the presence of humans they don't like”

When potentially dangerous animals are nearby, tamarin alarm calls kick into high gear – and they're often accompanied by 'mobbing' behaviours (like lunging, tongue flicking and generally harassing the threatening target). It was while studying these mobbing vocalizations in response to humans at the zoo that researchers noticed something interesting: when the monkeys were in the presence of a staff member they associated with danger (according to the study, this particular zoo keeper had been involved in their capture), they acted in an unexpected way. Instead of the anticipated mobbing tactics, the tamarins increased their vigilance and approached the target cautiously before quickly withdrawing again. And instead of loud alarm calls, they produced vocalisations that were so quiet that researchers initially failed to detect them at all (picking up on them only after recordings of the calls were amplified). 

So what was going on? The researchers write: "Although it is unclear what the motivational state of the tamarins was when in presence of the supervisor, it appears that they were responding to him as an ambiguous threat and may have been investigating the situation by cautiously approaching him to determine the actual level of threat and communicating to each other the appropriate behavioural response to take."

So it seems that, like humans, tamarins are given to speaking in hushed tones to avoid being overheard when someone mean and nasty is nearby. Such whisper-like behaviour has been observed in very few animal species, and never before in non-human primates ... but the researchers think it may occur among other primate species – we just haven't been able to eavesdrop on it yet!

The study was published in the journal of Zoo Biology.