"Long before it's in the papers"
September 11, 2007

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Monkeys “baby talk” young

Aug. 24, 2007
Courtesy University of Chicago
and World Science staff

Fe­male rhe­sus mon­keys make spe­cial sounds when in­ter­act­ing with in­fants, some­what like the “ba­by talk” peo­ple use with their young, re­search­ers have found. But sur­pris­ing­ly, the an­i­mals seem to use these calls only when show­ing ex­cite­ment about oth­er fe­males’ off­spring, not their own.

Courtesy Dario Maestripieri, U. Chicago
Hu­man moth­ers’ gen­tle, sing­song chat­ter to­ward in­fants—al­so called “moth­erese”—is a “high-pitched and mu­si­cal form of speech, which may be bi­o­log­i­cal in orig­in,” said Da­ri­o Ma­es­t­ri­p­i­eri of the Un­ivers­ity of Chi­ca­go, one of the sci­en­t­ists.

Spe­cial mon­key calls known as “gir­neys,” like moth­er­ese, seem to serve to “at­tract young in­fants and en­gage their at­ten­tion,” he said. Why mon­keys don’t make the calls to their own off­spring is un­clear; may­be the nov­el­ty of see­ing some­one else’s ba­by is what sti­m­u­lates them, he sug­gested.

His team stud­ied a group of free-ranging rhe­sus macaques on an is­land off Puerto Rico. They ana­lyzed calls ex­changed among adult fe­males and found that the number of gir­neys, as well as “grunts” that these mon­keys some­times make, 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 made calls, sug­gest­ing these were meant for the ba­by.

“Adult fe­males be­come highly aroused while ob­serv­ing the in­fants of oth­er group mem­bers,” said Jes­si­ca Whi­tham of the Brook­field Zoo near Chi­ca­go, lead au­thor of a pa­per on the find­ings. She in­ves­t­i­gated the mon­keys as a doc­tor­al stu­dent at the un­ivers­ity. “While in­tently watch­ing in­fants, fe­males ex­cit­edly wag their tails and emit long strings of grunts and gir­neys,” the re­search­ers wrote in the pa­per, pub­lished in the Sep­tem­ber is­sue of the re­search jour­nal Eth­ol­o­gy. 

When adult fe­males call to in­fants, Whi­tham and col­leagues said, the moth­ers in­fer that the adults just want to play with the in­fants and probably won’t harm them. Thus, the vo­cal­iz­a­tions may smooth adult fe­males’ in­ter­ac­tions with both in­fants and their moth­ers. For in­stance, the re­search­ers not­ed that the grunts and gir­neys were some­times fol­lowed by an ap­proach and groom­ing of the moth­ers.

“The calls ap­pear to be used to elic­it in­fants’ at­ten­tion and en­cour­age their be­hav­ior. They al­so have the ef­fect of in­creas­ing so­cial tol­er­ance in the moth­er and fa­cil­i­tat­ing the in­ter­ac­tions be­tween fe­males with ba­bies in gen­er­al,” they wrote. All this “re­sults in a rel­a­tively re­laxed con­text of in­ter­ac­tion where the main fo­cus of at­ten­tion is the baby.”

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Female rhesus monkeys make special sounds when interacting with infants, somewhat similar to the “baby talk” humans use with their young, researchers have found. But surprisingly, the animals seem to use these calls only to show their excitement about other females’ offspring, not their own. Human mothers’ gentle, singsong chatter toward infants—also called “motherese”—is a “high-pitched and musical form of speech, which may be biological in origin,” said Dario Maestripieri of the University of Chicago, a member of the research team. Special monkey calls known as “girneys” may, like motherese, seem designed to “attract young infants and engage their attention,” he said, as well as help reassure the infant’s mother that the caller means it no harm. Why monkeys don’t make the calls to their own offspring is unclear. Maybe the novelty of seeing someone else’s baby is what stimulates them, Maestripieri said. His team studied a group of free-ranging rhesus macaques that live on an island off Puerto Rico. They studied the calls exchanged among adult females and found that sounds known as grunts and girneys 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 made calls, suggesting these were meant for the baby. “Adult females become highly aroused while observing the infants of other group members,” said Jessica Whitham of the Brookfield Zoo near Chicago, lead author of a paper on the findings. She investigated the monkeys as a doctoral student at the university. “While intently watching infants, females excitedly wag their tails and emit long strings of grunts and girneys,” the researchers wrote in the paper, published in the September issue of the research journal Ethology. When adult females call to infants, Whitham and colleagues said, the mothers infer that the adults just want to play with the infants and probably won’t harm them. Thus, the vocalizations may facilitate adult females’ interactions with both infants and their mothers. For instance, the researchers noted that the grunts and girneys were sometimes followed by an approach and grooming of the mothers. “The calls appear to be used to elicit infants’ attention and encourage their behavior. They also have the effect of increasing social tolerance in the mother and facilitating the interactions between females with babies in general,” they wrote. “Thus, the attraction to other females’ infants results in a relatively relaxed context of interaction where the main focus of attention is the baby.”