Primates and Other Animals That Communicate through Ultrasound [SLIDESHOW]

One of the world's smallest primates, the Philippine tarsier, can communicate in ultrasound, a range of high-pitched noise inaudible to humans, according a new study published in the British Royal Society journal Biology Letters. The study, "Primate communication in the pure ultrasound", notes that the tarsier is the only primate known to communicate in this way.

Any sound above 20 kilohertz (20,000 hertz) is considered ultrasound, and is above the range of human hearing, due to limitations of the middle ear, which acts as a low-pass filter, cutting off sound above that range. Many animals have the ability to not only hear ultrasound, but produce it as well.  Click through the slideshow to see what some of those animals are.

A primate related to monkeys and lemurs, the Philippine tarsier is one of Earth’s smallest mammals, only growing to the size of a human fist. It is known to produce a loud, piercing call that is associated with territory disputes and a soft, birdlike sound when content. The recent study discovered that the tarsier can also produce ultrasound in frequencies around 70 kHz (70,000 Hz), and can hear sounds as high as 90 kHz (90,000 Hz).
The ability to produce these sounds gives the primate an advantage over their predators, according to the study. “Ultrasonic calls can be advantageous to both the signaller and receiver as they are potentially difficult for predators to detect and localise,'' it said.

Bats use ultrasound for navigation, called echolocation, but the way they do differs by species. Some bats use “low duty cycle echolocation,” where they use short clicks to send out an ultrasound call and listen for the echo, which gives them the ability to estimate the distance to their prey.
Other bats use “high duty cycle echolocation.” Bats who utilize this type of ultrasound emit a continuous call and take advantage of the Doppler shift, where there is a change in the frequency of a sound as the producer and listener move towards (or away) from each other, to estimate their prey’s location.

The concave-eared torrent frog, native to China, is the first frog and the first non-mammalian vertebrate to use ultrasound. The natural habitat of the frog is near rapidly flowing water, and researchers believe the 128 kHz (128,000 Hz) sound produced by these frogs developed so they could communicate with each other over the immense background noise that would otherwise drown out normal croaks.

Toothed whales, such as dolphins, porpoises, killer whales and sperm whales have a fatty organ called a melon in their heads, which helps to direct a focused beam of high-frequency ultrasound clicks in the direction their head is pointing. This echolocation works similar to low duty cycle echolocation in bats. These animals emit the clicks and wait to hear the return to estimate how far away their prey is. Their underwater habitat facilitates this feature, as sound travels better in water.

The tiger moth produces ultrasound not to communicate, but as a defense mechanism. By producing ultrasound of its own, it is able to ward off bats by acting as a radar jammer, confusing the bats so that the moths cannot be located. By doing this, they add another weapon to their survival repertoire that already includes poison.