Vocal babbling in a wild parrot shows life history and endocrine affinities with human infants

Vocal babbling is a critical phase in infant language development and is best understood in temperate songbirds where it occurs primarily in males at reproductive maturity and is modulated by sex steroids. Parrots of both sexes are famous vocal imitators but a vocal babbling stage has gone unnoticed and it is not clear how the endocrine system is involved.  We report on vocal babbling in both sexes of nestling wild green-rumped parrotlets (Forpus passerinus) in Venezuela. In addition, we show that corticosterone supplements resulted in individuals with larger repertoires after treatment had ended. Results indicate parrotlets begin babbling during an earlier life history stage compared to most songbirds and one in which corticosteroids play an important role. Here we include audio files of bouts of babbling from a sample of audio-video recorded inside specially designed nest cavities and a data set of spectrographic measurements taken on each element within each bout of babbling as well ...