Whispering can be a smart way to have a private conversation. So it’s not surprising that other species—from corn borer moths to ground squirrels to certain fish—do something like it, too. Now, researchers have added the first nonhuman primate species, cotton-top tamarins (Saguinus oedipus), to the list. The discovery was made at New York City’s Central Park Zoo during an experiment designed to capture alarm calls that the tamarins reportedly make when afraid of people. But instead of making the calls when a worker they feared stepped inside their enclosure, the tamarins seemed to fall silent, the researchers report online this week in Zoo Biology. Only when the scientists analyzed spectrograms (graphical representations of the sounds) did they realize the tamarins were whispering their calls instead of shouting them. Leading evolutionary scientists had predicted that whispers would likely be found in highly cooperative species like the tamarins, because it’s an easy way to avoid eavesdroppers. You can hear a tamarin’s sharp chirp above. Actually, if you could hear the soft chirp, you’re most likely a tamarin.