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Developmental Neuroethology at the Eunice Kennedy Shriver National Institute of Child Health and Human Development

Primate Behavior

The cry sounds of infant marmosets: early vocal behavior during brief periods of social separation

All mammals begin life with a limited range of vocalizations, yet over the course of maturation, many mammals come to possess a broad range of functionally diverse communication sounds as adults. Perhaps the most universal infant vocalization is given during periods of distress, such as separation from a parent or other caregiver, when hungry, cold or simply in need of attention. In human infants, such sounds are typically referred to as ‘crying.’ Classification schemes of the calls of non-human mammals generally do not include a ‘crying’ category, despite the fact that vocalizations with similar functional and acoustic properties as human cry sounds are present. An extensive literature on human crying and cry sound acoustics has yet to be matched by extensive study on infant crying in animals, partly as a result of the difficulty of recording the intimate details of infant behavioral development in many mammals, partly due to the opportunistic occurrence of these sounds, and perhaps partly due to a widespread lack of appreciation of the importance and existence of these non-human equivalents of human infant crying.

Our lab uses a procedure for eliciting cries from infant primates that is safe for the infant, successful in reliably inducing crying, and has led to extensive studies of crying behavior in several species of non-human primate. This involves separating (as gently as possible) the infant from its caregiver (infant monkeys are usually carried by the mother or, in marmosets, by either parent or older brother or sister). Older infants that have started to achieve some independence can often be coaxed into a transport cage without being picked up. The infant is then brought to a quiet room with no other monkeys present. Under these conditions, infants typically start crying (we call these vocalizations ‘isolation calls’) and 5 or 10 minutes is usually sufficient to obtain enough vocal data for detailed analysis. The infant is then returned to its home.

Photos by Catherine Depeine

Representative Marmoset Vocalizations

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