Tiny tarsier's ultrasonic sound

Philippine tarsier. The Philippine tarsier (Tarsius syrichta), a 5-inch tall Southeast Asian primate, has long resembled a ventriloquist's doll. It would open its mouth as though chattering away, but researchers heard nothing. Now, a new study in Biology Letters has found out why: the Philippine tarsier communicates ultrasonically, surpassing all other primates, and nearly all terrestrial mammals, in its ability to create sounds in the upper registry.
The tarsiers communication is "comparable to the highly specialized vocalizations of bats and dolphins, which are used primarily for echolocation," says lead author Nathaniel Dominy with Dartmouth in a press release. He calls the Philippine tarsier's sounds "extreme," and listening to a sample slowed down eight times so we can hear it, one comprehends the adjective.
While humans can hear up to 20 kilohertz, Dominy and colleagues measured the Philippine tarsier communicating at levels around 70 kilohertz and up to 91 kilohertz (anything above human range is generally considered "ultrasonic").
For a small primate like the tarsier, which is considered a "living fossil" since it is practically unchanged evolutionarily for 45 million years, ultrasonic communication is likely an important tool for avoiding predators. The tarsier is free to communicate without allowing predators to eavesdrop. The ability to hear such levels may also help the tarsiers find insect-prey. In addition,the paper notes the sounds could also be used for alarm calls, rivalry, and social interactions.
"Our findings not only verify that tarsiers are sensitive to the ultrasound, but also that [the Philippine tarsier] can send and receive vocal signals in the pure ultrasound," Dominy says.
This doesn't mean all other tarsier species communicate via ultrasonic sounds. Other tarsier's calls are audible to humans, although Horsfield's tarsier (Tarsius bancanus), found on Borneo and Sumatra, may be similar to the Philippine tarsier in that it seems to call, but no sounds are heard.
Sporting massive eyes, tarsiers are nocturnal and feed on a variety of insects, as well as snakes, birds, and bats.