14 DAY TRIAL // A species of primates native to the southeastern parts of Asia, called the Philippine tarsiers (Tarsius syrichta), were discovered to communicate with each other using ultrasounds. This is a nearly-unbreakable code, and no other species of primates is known to use it.
The sounds they make are above the highest sounds the human ear can perceive. They are basically in the same range as bats and mice. The latter two however produce sounds in the human spectrum as well. We can hear frequencies spanning from 20 hertz to around 20,000 hertz.
T. syrichta can produce noises above 20 kHz, which basically conceals their communications from most other animals. Some birds are capable of hearing some portions of the ultrasound frequency range, as this is one of their evolutionary adaptations to their environment.
But the fact that the small primates – which are no larger than a human hand – can do the same is outstanding. One of the possible explanations for why this trait exists is that it developed in order to allow the primates to steer clear of predators.
Via this ability, they can pass alarm calls from one another without alerting their potential predators that they know they are being hunted. However, this ability is not used very often, primary due to practical reasons having to do with the behavior of ultrasounds.
Noises emitted at these frequencies have the tendency to travel very fast, but they are also very difficult to trace back. If an alarm call, for example, is sent out from a great distance, the animals it's addressed to may have a hard time identifying the source of the signal.
The announcement was made by Humboldt State University anthropologist and study co-author Marissa Ramsier. She conducted the work with study co-author Sharon Gursky-Doyen, who is a biological anthropologist at the Texas A&M University in College Station.
They decided to conduct ultrasound investigations after observing that the primates were opening their mouths as if about to shout, but no sounds came out. When they listened to the creatures in ultrasound wavelengths, they detected a flurry of signals.
“Philippine tarsiers have often been described as quiet. [However,] they're screaming and talking away, and we just didn't know it,” Ramsier explains, quoted by Science Now. She adds that the primates are able to produce sounds at frequencies reaching 70 kilohertz, 3.5 times higher than humans can hear.
Anthropologists believe that most of the ancient mammals which lived on Earth used these frequencies to communicate. The vast majority of species that did that have long since gone extinct, but the trait may have endured in species such as T. syrichta.