Department of Biology, University of Texas Rio Grande Valley, Brownsville, TX, USA.
Departmento de Biología, Universidad de Carabobo, Valencia, Venezuela.
Proc Biol Sci. 2022 Jun 8;289(1976):20220592. doi: 10.1098/rspb.2022.0592. Epub 2022 Jun 1.
Prelinguistic 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 icons of tropical vocal plasticity, but vocal babbling is unreported in this group and whether the endocrine system is involved is unknown. Here we show that vocal babbling is widespread in a wild parrot population in Venezuela, ensues in both sexes during the nestling stage, occurs amidst a captive audience of mixed-aged siblings, and is modulated by corticosteroids. Spectrographic analysis and machine learning found phoneme diversity and combinatorial capacity increased precipitously for the first week, thereafter, crystalizing into a smaller repertoire, consistent with the selective attrition model of language development. Corticosterone-treated nestlings differed from unmanipulated birds and sham controls in several acoustic properties and crystallized a larger repertoire post-treatment. Our findings indicate babbling occurs during an early life-history stage in which corticosteroids help catalyse the transition from a universal learning programme to one finely tuned for the prevailing ecological environment, a potentially convergent scenario in human prelinguistic development.
前语言咿呀学语是婴儿语言发展的关键阶段，在温带鸣禽中最为明显，这种现象主要发生在性成熟的雄性身上，并受性激素调节。雌雄鹦鹉都是热带声音可塑性的代表，但在这个群体中没有报告过发声咿呀学语，也不知道内分泌系统是否参与其中。在这里，我们表明在委内瑞拉的一个野生鹦鹉种群中广泛存在发声咿呀学语，在雏鸟阶段的两性中都会出现，发生在由不同年龄的兄弟姐妹组成的圈养观众中，并受皮质类固醇调节。光谱分析和机器学习发现，前一周音素多样性和组合能力急剧增加，此后，逐渐形成一个较小的音库，与语言发展的选择性衰减模型一致。皮质酮处理的雏鸟在几个声学特征上与未经处理的鸟类和假对照不同，并且在处理后形成了更大的音库。我们的发现表明，咿呀学语发生在生命早期的一个阶段，在此期间，皮质醇有助于催化从普遍的学习计划到适应当前生态环境的精细调整，这是人类前语言发展中的一个潜在趋同情景。
