As far as the cotton-top tamarins at New York’s Central Park Zoo are concerned, there is one zoo supervisor that is enemy number one. He was a part of the team that captured them in the wild and he is always around to supervise the tiny primates’ medical procedures. As soon as he comes around, the monkeys start whispering to each other – a new discovery that has scientists talking as well.
City University of New York researchers, Rachel Morrison and Diana Reiss, were using the zoo to study primate communication when they noticed the whispering behavior. They had been trying to elicit an “alarm call” (a loud screatch to notify the arrival of a predator) by having the zoo supervisor walk into the tamarin’s enclosure. They had picked this particular supervisor because of his history with the tamarins. In the past, they had even “mobbed” him, making ear-splitting noises and lunging at him. The researchers expected the creatures to do the same again, and had video and audio recorders set up to capture it. Instead, what they witnessed was that the primates appeared to go silent.
Upon later analysis of the recordings, the researchers amplified the sound and discovered that the one-pound creatures were in fact making very soft chirps, too low for the humans to hear. The scientists deduced that these whispery chirps, called “low amplitude signaling,” were a more cautious type of alarm.
There are a handful of animals that whisper. A female fish, called the croaking gouramis, will whisper purrs to its mate to initiate sex and one species of bat, the barbastelle, uses whispering as a technique to avoid detection by moths with ears, so that they can eat them. But up until now, no one has caught a monkey or an ape in the act, making the tamarins the first non-human primates to whisper. They are also the first animals to use whispering for the same reason that we do: to avoid being overheard by an unwelcome guest or predator.
Morrison and Reiss, who published their results in Zoo Biology, acknowledge that it is impossible to know for sure what the monkeys are saying to each other. However, by observing their behavior, they surmised that the tamarins were warning each other about the threat while trying to avoid detection. They also suspect that other species may also whisper for the same reason, but so far, no one has heard them.