Zoologists know that some animals like to whisper, or do something like it, under certain circumstances. But it's never been observed in nonhuman primates... until now.
The primate in question is the cotton-top tamarin (Saguinus oedipus), one of the world's smallest primates. It lives in the tropical forests of northwestern Columbia in South America.
Its whisper-like behavior was discovered at New York City's Central Park Zoo during an experiment intended to record the alarm calls of tamarins when afraid of people. But instead, when a distrusted zoo worker walked in, the tamarins fell silent.
Later, when the researchers analyzed audio spectrograms, they realized that the tamarins were in fact communicating, but at an extremely hushed level (low amplitude vocalizations):
The researchers, Rachel Morrison and Diana Reiss, say it's potential evidence of convergent evolution in communication strategies among highly social and cooperative species.
Read the entire study at Zoo Biology: "Whisper-like behavior in non-human primate."
Related: A Beluga whale mimicking human speech.