The Philippine tarsier is a tiny primate with a seriously high voice. The saucer-eyed mammal can let out (and listen to) squeaks and squeals at such a high frequency that it effectively gives the mammal a private communication channel.
A team of researchers, led by Marissa Ramsier of Humboldt State University in California, found that the tiny tarsier can hear and emit sounds in the ultrasound range -- that's above 20kHz.
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Most humans can't hear in that range, and a dog whistle is pitched to be just inside ultrasound, somewhere between 22 and 23 kHz. A handful of mammals can make sounds in this range -- some whales, domestic cats and a few species of bats -- but few can match the Philippine tarsier.
When issuing warnings or ferreting out crickets for a nighttime snack, the nocturnal faunivores (that's a mix of carnivore and insectivore) can vocalise in a range around 70 kHz, and pick up frequencies above 90 kHz.
"Such values are among the highest recorded for any terrestrial mammal," the researchers note in their paper, which was published in Biology Letters.
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To get this reading, they captured six of the docile creatures and placed them inside custom-built sound chambers to test their sensitivity to high-pitched sounds. Then, they recorded another 35 specimens in the wild to measure the frequency of the tarsier's chatter.
In the paper, the researchers explain that, "ultrasonic alarm calls can be advantageous to both the signaller and receiver as they are potentially difficult for predators to detect and localise." Being able to hear in high ranges might let them eavesdrop on noises made by moths, crickets and birds.
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