If you’ve ever walked into a room of people who all suddenly become quiet, you’ll know the unpleasant feeling of being talked about behind your back. A supervisor at New York City’s Central Park Zoo is experiencing a similar situation, except instead of the offenders being other people, they’re a group of cheeky monkeys called cotton-top tamarins.
Humans whisper to prevent other people from eavesdropping on conversations that you may not want them to hear. Although there is some evidence for whisper-like behaviour in a few other species, there have been no reported cases in non-human primates—until now.
“We discovered the first evidence of whisper-like behavior in a non-human primate, the cotton-top tamarin (Saguinus oedipus), in the course of investigating their use of human-directed mobbing calls,” the psychology researchers at the City University of New York, Rachel Morrison and Diana Reiss, stated in their paper, published in the journal Zoo Biology.
Tamarins are known for making a wide variety of noises for different circumstances, such as feeding, group bonding, mild alarm and investigation. Mobbing calls are the sounds the monkeys make to confuse or intimidate predators when they feel threatened. The researchers wanted to study the tamarins at the zoo to learn more about these particular calls. They organised for a particular zoo keeper whom the monkeys had mobbed previously to enter their enclosure while the researchers video and audio recorded the animal’s behaviour and vocal responses. Instead of producing loud, mobbing calls, the tamarins did just the opposite: they appeared to be making no noise at all. It wasn’t until the researchers played back the recordings on their spectograms—visual representations of sound—that the researchers discovered that the tamarins were making noises of such low amplitude that even the supervisor in the enclosure with them couldn’t hear. They were whispering to each other.
Although it’s impossible to know what exactly the monkeys were saying to each other, the researchers suggest that the tamarins’ response was more of a cautious type of alarm. The animals might not be sure of what this potential threat held in store for them and were ‘discussing’ the proper response without letting the supervisor know.
This discovery has led the to believe that whispering occurs in other species as well—we just haven’t heard them yet.
If a person (or any other animal) is whispering, they are speaking very softly. This is usually done to prevent someone else from hearing or listening in to a conversation. Whispering requires no vibration of the vocal chords. You can test this out by placing your fingers gently against your throat and speaking normally, and then whispering.