Tarsiers - Tiny Primates With Ultrasonic Vocal Skills - NYTimes.com One of the world's smallest primates turns out to be the only one that is ultrasonic, making and receiving calls that are outside the range of human hearing. The animal is the tarsier, a five-inch-tall creature with pointy ears and large, round eyes. Tarsiers (pronounced TAR-see-ers) are considered endangered and are found only on islands in Southeast Asia - the Philippines, Sulawesi, Borneo and Sumatra. Tarsiers are nocturnal and hard to spot in the wild (and are not found in any zoos). So for a study that appears in a recent issue of the journal Biology Letters, researchers had to rely on hunter-gatherers in the Philippines to help them capture six tarsiers. They then used audio equipment to record the ultrasonic calls. "Some primates have calls that contain small components of ultrasound," said one of the authors, Nathaniel J. Dominy, an anthropologist at Dartmouth University. But tarsiers produce calls that are entirely in the ultrasound. The scientists also noticed that the tarsiers seemed to open their mouths and make high-frequency calls when in the vicinity of humans, possibly to raise an alarm. The animals may use the same tactic to warn companions when predators like snakes or owls are nearby. Only a handful of other mammals, including domestic cats, some bats and rodents, make ultrasonic calls. Tarsiers are also the only primates that feed entirely on small creatures like insects, geckos and lizards. These prey make ultrasonic sounds, too, and tarsiers may be listening for them, Dr. Dominy said.