One of the world's smallest primates, the Philippine tarsier, communicates in a range of ultrasound inaudible to predator and prey alike, according to a study published on Wednesday.
No bigger than a man's hand, Tarsius syrichta can hear and emit sounds at a frequency that effectively gives it a private channel for issuing warnings or ferreting out crickets for a nighttime snack, the study found.
Only a handful of mammals are known to be able to send and receive vocal signals in the ultrasound range, above 20 kilohertz (kHz), including some whales, domestic cats and a few of the many species of bats.
And few of these can squeal, screech or squawk at the same sonic altitudes as the saucer-eyed tarsier, which up to now had been mistakenly described as being "ordinarily silent," researchers found.
Its finely-tuned ears are capable of picking up frequencies above 90 kHz, and it can vocalise in a range around 70 kHz.
By comparison, humans generally can't hear anything above 20 kHz, and a dog whistle is pitched to between 22 and 23 kHz.
A team of scientists from the United States and the Philippines led by Marissa Ramsier of Humboldt State University in California gathered their inaudible results in two ways.