Infant 'Babbling' in a Nonhuman Primate: Complex Vocal Sequences with Repeated Call Types

Abstract

The pygmy marmoset is a small South American primate with a complex social system based on cooperative breeding. Infant pygmy marmosets are extremely vocal; most of their calling is a repetitive pattern of mixed call types that is babbling-like. In a longitudinal study of vocal development in 8 infant pygmy marmosets, we recorded more than 750 calling bouts which occurred in a wide range of behavioural contexts. The infants used 16 different call types that we grouped into three categories: Adult-Like (acoustic structure consistent with that of adult calls), Adult-Variant (acoustic structure with some adult features and some variable features), and Infant (absent from the adult repertoire). The calling bouts were highly conspicuous in their duration (ranging up to more than 6.5 min/bout), complexity (up to 10 different call types/bout), and call rate with nearly 3 calls/s. When the infants were older, their call rate slowed and they shifted to using several of the Adult-Like calls with greater frequency, and used fewer Adult-Variant types. The infants did not use the Adult-Like call types appropriately when compared to the typical adult usage of those types. Caregivers were significantly more likely to respond to an infant when it was vocalizing than when it was not.

Limiting parental feedback disrupts vocal development in marmoset monkeys

“…Besides infant ‘babbling' sequences and immature call types, such as cries and compound cries, S1 monkeys still produced a large number of trill calls (>60%), mostly while ‘babbling', as it has been reported for marmoset infants before25. The vocalizations of the litters also differed in distinct call parameters.…”

“…Normally, under these conditions, subadult and adult monkeys exhibit adult call repertoire, whereas infants produce infant-specific call strings, so-called ‘babbling', that is characterized by the utterance of both immature and mature call types with short inter-call intervals (200–800 ms)2425. In the given situation, all five monkeys, including the hand-raised sibling, produced a variety of adult call types (Fig.…”

Babbling behavior in the sac-winged bat (Saccopteryx bilineata)

“…Occurrence of infant babbling and evidence for babblinglike vocalizations was reported for a number of primate species (see Elowson et al 1998b). Our study documents infant babbling in sac-winged bat pups.…”

The autonomic nervous system is the engine for vocal development through social feedback

“…Such transient vocalizations are also evident during song learning by birds [22**]. Unlike Old World nonhuman primates, developing marmosets also produce a babbling-like vocal output [23, 24**, 25], with some vocalizations that sound adult-like (but are produced in the wrong social context) and others that are immature forms of what will ultimately be the contact (“phee”) call used by it during vocal exchanges (Figure 1A) [24**,26**]. …”