Figure 1.

A hypothesized comparative summary of relations between babbling and vocal production learning (VPL) in selected taxa. The top four rows represent taxa for which at least some form of vocal learning is known. The first column represents known vocal-learning characteristics. I, imitation; N, incorporation of novel sounds; AM, acoustic modification; AMI, auditory–motor integration; S, social feedback. Columns represent crude developmental stages (width is arbitrary). All vocal learners show a stage of babbling as well as calls, but babbling onset may differ. Although vast numbers of vertebrates produce vocalizations communicatively, many have never been reported to show VPL or babbling. The term ‘calls’ in the figure refers to vocalizations that are communicative already at developmental onset (in contrast to song), with varying amounts of VPL. Calls may or may not be part of babbling depending on the call and the species. Song in songbirds, hummingbirds and greater sac-winged bats is shaped by VPL. The figure summarizes data from a variety of species that appear to support the working hypothesis that babbling or some form of precursor vocalization in infancy may be a requirement for VPL, which often results in complex mature vocal repertoires.