Can’t hear tarsier? It silently ‘talks’ in ultrasound

BOHOL TARSIERS A new study published on Wednesday says tarsiers communicate with one another using ultrasound frequencies inaudible to man and many species of predators. EDWIN BACASMAS

PARIS—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 creatures 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.

The tarsier’s finely tuned ears are capable of picking up frequencies above 90 kHz, and it can vocalize in a range around 70 kHz.

By comparison, humans generally can’t hear anything above 20 kHz, while a dog whistle is pitched to between 22 and 23 kHz.

Inaudible results

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.

First, the scientists captured six of the docile nocturnal creatures and placed them inside custom-built sound chambers to test their sensitivity to high-pitched sounds.

After the experiments, the rare and endangered animals were returned unharmed to their natural habitat on the Philippine island of Mindanao.

To measure the frequency of the tarsier’s ultrasound chatter, the researchers recorded another 35 specimens in the wild.

“The minimum frequency of the call—67 kHz—is the highest value of any terrestrial mammal, excluding bats and some rodents,” said the study that was published in the British Royal Society’s Biology Letters.

Vocal acrobatics

What advantages do the tarsier’s high-end vocal acrobatics confer? There are several, according to the researchers.

One is being able to sound a silent alarm.

“Ultrasonic calls can be advantageous to both the signaller and receiver as they are potentially difficult for predators to detect and localize,” the researchers explained.

The tarsier’s exceptional hearing may also facilitate acoustic eavesdropping on noises emitted by its prey, which range from crickets and cockroaches—their staple diet—to the occasional moth, katydid or hatchling bird.

Finally, the study speculated, the tarsier’s ability to communicate in ultrasonic ranges filters out all the low-frequency “noise” and hubbub of a tropical environment.

Tarsier’s have five-digit hands that eerily resemble—in emaciated form—their human counterparts.

Lacking the typical “night vision” of other nocturnal creatures, tarsiers also have—in relation to their body size—the largest eyes of any primate on Earth. AFP

Originally posted at 05:59 pm | Wednesday, February 08,  2012