Shhhh! Researchers say they found the tamarin monkeys at New York\'s Central Park Zoo lower their voices to keep others from eavesdropping -- much like humans. After they first noticed the tamarins whispering in the zoo, researchers said they hoped to learn a more about the types of calls that these primates make to each other under different circumstances, Science World Report reported Thursday. Previous research indicated the monkeys could make a wide range of noise. During their inquiry, researchers said they hoped to record the alarm call of the tamarins -- but found the monkeys fall silent when a zoo worker entered their space. When they listened to the audio recordings, they realized the primates weren\'t really silent, but had lowered their voices when communicating. The behavior is known as \"low amplitude signaling,\" which, in the case of the monkeys, is very soft chirps, Science World Report said. While it\'s impossible to know what these monkeys were \"whispering\" to each other, the researchers offered some theories, the science publication said. Most likely, researchers theorized, the monkeys were reminding each other of the threat the man posed in such a way that wouldn\'t alert the intruder. The findings were important to help better understand the behavior of tamarin monkeys while revealing non-human primates can whisper to keep from being overheard, Science World Report said. The findings were published in the journal Zoo Biology.