[Formation of passerine (Passeriformes) vocalization in ontogeny: the current state of the problem]

It the acoustic signal system of birds, songs and calls are distinguished. Up to the late 1970s, the attention of researchers was focused primarily on studying the process of song formation; the patterns of the call system formation remained virtually unstudied. In this field, the prevailing notion was that, since all calls are hereditary, their formation in the repertoire of all birds is similar. This notion was based on non-passerine birds, for which calls constitute most of the vocal communication. Most calls can, indeed, be formed without learning, even in nestlings raised in isolation. Yet some calls remain and are transferred in populations only through learning. The stages of sound repertoire development reflect crucial reorganizations of the acoustic behaviour of nestlings and are distinctly recognizable in most of the studied birds. The first three stages coincide with the periods of postnatal development of altricial birds distinguished by researchers from other fields (based on morphological, behavioural, and physiological characters). These are the early nestling, later nestling, and post-nestling periods. Two more periods may, however, be distinguished in the formation of vocalization: the fourth, confined to the period of hormonal reorganization of the organism during the autumn moult, and the fifth, coinciding with the beginning of the first reproductive cycle of the young bird. The formation of calls in representatives of different systematic groups (to families inclusive) can follow three principal paths: independent, successive, or explosive. Data on the development of the specific repertoire of acoustic signals in ontogeny can serve as a reliable taxonomic criterion, assisting in reconstructing and specifying phylogenetic relationships between different bird lineages.