Listen to a recording of the tarsier’s ultrasonic call, slowed down eight times to be audible to humans. Credit: Nathaniel Dominy
Tiny primates in South-East Asia called tarsiers can produce ultrasonic calls, high above frequencies that are audible to humans, according to a new study published online in Biology Letters on Feb. 8.
Tarsiers grow up to about 5 inches (13 cm) in height, and are nocturnal. They feed mainly on insects as well as small vertebrates like lizards.
Although some species emit calls that humans can hear, those found in Borneo and the Philippines appear to be silent, suggesting that their vocalizations are ultrasonic. The calls are used in social interactions, such as deterring rivals and to convey alarm.
Led by Nathaniel Dominy from Dartmouth College, a team of scientists studied the Philippine tarsier, Tarsius syrichta, on the islands of Mindanao, Bohol, and Leyte.
They discovered that these primates can detect sounds at up to 91 kilohertz (kHz), which is higher than the known range of any other primate species, and indeed most animals. Normally humans cannot hear sounds above 20 kHz.
A number of the tarsiers produced calls at about 70 kHz with a tone-like structure like those of other species. They gave out these calls when the researchers were nearby, indicating that this was probably a silent alarm to alert others to the presence of danger.
“Our findings not only verify that tarsiers are sensitive to the ultrasound, but also that Tarsius syrichta can send and receive vocal signals in the pure ultrasound,” said Dominy in a press release.
Such calls create “private channels of communication with the potential to subvert detection by predators, prey, and competitors,” concluded the scientists in their paper
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