[Meaning and Mechanisms of Birdsong: Inspiration for Pneumology]

Abstract

In contrast to humans, the location where sound is produced in birds is not the larynx, but rather the so-called "vocal box" (scientific term "Syrinx"). In some species the syrinx is located at the bifurcation point of the trachea into the two main bronchi (tracheal vocal head), while in some in the main bronchi (bronchial vocal head). During inspiration, part of the air flows into the lungs, and the part needed for singing flows into the air sacs adjacent to the lungs. During expiration, air leaves the air sacs and flows through the syrinx, where the song is created. When birds sing in two voices at the same time, individual sequences are formed simultaneously in the right and left parts of the syrinx.The song analysis is based on spectrograms (so-called sonagrams), which graphically represent the frequency spectrum of bird song.The song consists of one or more verses, which in turn consist of the variable or constant sequence of motives or syllables. Some songbirds have an enormous repertoire of syllables and verses (max. up to 7000 verses per day). In addition to singing, most bird species also have much simpler begging, contact, threatening, flight, alarm and copulation calls.Male birds sing primarily for two reasons: 1. They use song to woo a potential partner. This song provides the females with important information about the applicant's performance and health. 2. Singing serves to defend the territory.In around 40 % of songbird species, females also sing. Pairs of some species sing in perfect synchronization.A number of songbirds imitate both the voices of other songbirds and ambient noises, and many songbirds have regional dialects.Song development depends on genetics and other factors such as the environment, metabolism and hormonal influences. It proceeds step by step and initially includes relatively primitive sequences (so-called "subsongs"), then leads through more complex intermediate forms ("plastic songs") and finally to the completed singing pattern ("full songs").Young birds learn the song of their species at a time when they are not yet singing themselves, often as nestlings aged 10 to 50 days from older members of the species, usually from their fathers.The song of young birds develops, based on the template of adult song, in a network of sensory-motor neurons in the forebrain.Songbirds, especially the zebra finch, currently offer the best model for the neural basis of human language learning. In birds, the so-called "High Vocal Center" orchestrates all brain regions relevant to songs, with the neural control of song being sensitive to sex hormones.