Female rhesus monkeys attract other mothers鈥� newborns with a form of 鈥渂aby talk鈥� that serves a similar function to the high-pitched babbling sounds humans make around babies, a study suggests.
Some non-human primates, such as rhesus macaques and squirrel monkeys, make unusual sounds, particularly grunts and nasal whines known as 鈥済irneys鈥�, in the presence of infants of their own species. In 1989, a group of researchers from the National Institute of Child Health and Human Development in Maryland, US, that squirrel monkey鈥檚 use special sounds to interact with their young.
However, in the case of macaques, experts have previously speculated that these sounds may be meant to reassure a baby鈥檚 mother that the infant will not be harmed. This is because female rhesus macaques are often aggressive and careless around infants that do not belong to them, and because the animals rarely make the sounds around their own young.
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鈥淵oung females who are inexperienced will harm babies,鈥� by dragging or dropping them, explains Dario Maestripieri at the University of Chicago, Illinois, US.
To test the hypothesis that the sounds are meant to reassure the infants鈥� mothers, Maestripieri鈥檚 colleague travelled to a small island off the coast of Puerto Rico. Here she studied 19 females living on the island over 12 months, noting the types of vocalisations they made in the presence of infants and their subsequent actions. She recorded their behaviour for a total of 317 hours.
Musical talk
To her surprise, analysis showed that the females were no less likely to mistreat an infant if they made grunts or girneys before approaching it. Furthermore, females seemed to direct 80% of their vocalisations towards the infant itself rather than the infant鈥檚 mother.
This suggests that the noises made by the macaques are not meant to reassure fellow females. Instead, she says, the noises most probably represent a unique type of vocalisation similar to the high-pitched, musical 鈥渂aby talk鈥� that humans use to get the attention of newborns, a type of vocalisation also known as 鈥溾��.
It is unlikely that the grunts and girneys convey any real information to the infants. So Whitham believes that the females simply want to get the infants鈥� attention and play with them.
Playing with another parent鈥檚 infants can be advantageous for a species as a whole, says , an expert on primate behaviour and the origins of language at Florida State University in Tallahassee, also in the US. 鈥淚t鈥檚 advantageous to be fascinated with babies if one day you鈥檒l have one of your own鈥�, he says.
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