WASHINGTON, Aug. 24 (Xinhua) -- Female rhesus monkeys use special vocalizations while interacting with infants, the way human adults use motherese, or "baby talk," to engage babies' attention, new research published Friday in the current issue of the journal Ethology by researchers from University of Chicago shows.

Motherese is a high pitched and musical form of speech, which may be biological in origin. In order to determine if other primates also use special vocalizations while interacting with infants, researchers studied a group of free-ranging rhesus macaques, which live on an island off the coast of Puerto Rico.

They studied the vocalizations exchanged between adult females and found that grunts and girneys (particular monkey vocalization)increased dramatically when a baby was present. They also found that when a baby wandered away from its mother, the other females looked at the baby and vocalized, suggesting that the call was intended for the baby.

"Adult females become highly aroused while observing the infants of other group members," explains lead author of the article, Jessica Whitham. "While intently watching infants, females excitedly wag their tails and emit long strings of grunts and girneys."

Researchers have long been interested in the noises that non-human primates make and how they are used for communication. Monkey vocalizations could be carrying information that the sender expects the recipient to understand, or they could be noises that the recipient can draw inferences from, but are not intended to carry information.

The new study showed that the grunts and girneys emitted by the rhesus macaques fall into the category of vocalizations not intended to convey specific information, and appear to be used to attract other individuals' attention or change their emotional states.

They also discovered that, unlike human mothers, the rhesus macaque mothers did not direct grunts or girneys toward their own offspring. It could be that the monkey mothers are familiar with their own offspring and use the vocalizations with other babies because they are excited about the novelty of seeing a new infant, researchers said.