Bird song refers to the sounds, usually melodious to the human ear, made by many birds of the order Passeriformes as a form of communication. Most song is emitted by male rather than female birds. The avian vocal organ is called the syrinx.
The anatomical and physiological mechanisms underlying the production of bird song, the acquisition of song during the life of individual birds, the acoustic structure of the songs, and their adaptive function in the social life of birds, have been the subject of intensive scientific study.
It has been known since time immemorial that the songs of different species vary, and are more or less characteristic of the species. Species vary greatly in the complexity of their songs and in the number of distinct kinds of song they sing; in some species, individuals vary in the same way. In a few species, however, for example starlings, songs incorporate arbitrary elements learned in the individual's lifetime, a form of mimicry. In many species it appears that although the basic song is the same for all members of the species, young birds learn the details of their songs from their fathers, and this allows variations to build up over generations, a form of dialect.
Researchers continue to explore why birds sing, but widely accepted evidence suggests major functions of bird song include intra-specific recognition, especially in advertising for mates, and defending territory.
Bird song is often imitated in music, especially song. Several classical composers have incorporated it into their music. Ludwig van Beethoven, for example, included imitations of the nightingale, quail and cuckoo in his Symphony No. 6 (the Pastoral). The French composer Olivier Messiaen had a particular interest in bird song, carefully notating many birds' cries and incorporating them into his music (his Catalogue d'oiseaux for solo piano is especially notable in this regard).
François-Bernard Mâche's Musique, mythe, nature, ou les Dauphins d'Arion (1983), includes a study of "ornitho-musicology" using a technique of Nicolas Ruwet's Language, musique, poésie (1972) paradigmatic segmentation analysis, shows that birdsongs are organized according to a repetition-transformation principle used to analyze human music.
Bird song is also a popular subject in poetry. Famous poems inspired by bird song include Shelley's To a Skylark ("Hail to thee, blithe Spirit!/Bird thou never wert") and Gerard Manley Hopkins' Sea and Skylark.
Birds learn songs early in life with subvocalizations that develop into renditions of adult birdsongs. Zebra finches, the most popular specimen used in birdsong research, develop a version of a familiar adult's song after 20 or more days from hatch. By around 35 days, the chick will have learned the adult song. By around 60 days rehearsal has perfected the song which after another 30 days, at sexual maturity, becomes invariant.
Research indicates bird song is a form of motor learning that involves regions of the basal ganglia. Models of bird song motor learning are sometimes used as a model for how humans learn speech, and indeed they share many similarities, such as requiring teachers, practice, error-correction, and eventually becoming more difficult after the bird or human reaches sexual maturity.
Researchers suggest birds learn songs, rather than inherit their sounds genetically. Research has hypothesized learned songs allow the development of more complex songs through cultural interaction, it allows interaspecies dialects that help birds stay with their own kind within a species, and it allows birds to adapt their songs to different acoustic environments. (Slater, 1989)
Birdsong learning occurs along neural pathways that connect the Hyperstriatum Ventralis, which is a region unique to the avian pallium, to the robust nucleus of the Archistriatum. The pathway traverses the paraolfactory lobe, the Dorso-Lateral division of the Medial thalamus, and the Lateral Magnocellular nucleus of the Anterior Neostriatum. (The neostriatum is similar to the putamen in the basal ganglia of mammals.) Cells in along the learning pathway accumulate testosterone, suggesting androgens might be involved in birdsong learning.
Birdsong production is generally thought to start at the nucleus Uvaeformis of the thalamus with signals emanating along a pathway that terminates at the syrinx. The pathway from the thalamus leads to the interfacial nucleus of the neostriatum, High Vocal Center, which is the Hyperstriatum Ventralis, then to the Robust nucleus of the Archistriatum, the Dorso-Lateral division of the Medial thalamus and to the tracheosyringeal nerve.
Disruptions along the learning pathway between 20 and 60 days of a finch's life permanently deprecates the bird's song, but has no effect if the same pathways were disrupted later in life. Disruptions along the production pathways can always disrupt a birds ability to sing.
Recent research in birdsong learning has focused on the Area Ventralis of Tsai, which produces dopamine to the paraolfactory lobe, the Lateral Magnocellular nucleus of the Anterior Neostriatum and the VentroLateral medulla. Other researchers have explored the possibility that the high vocal center is responsible for syllable production, while the robust nucleus of the archistriatum, the primary song output nucleus, may be responsible for syllable sequencing and production of notes within a syllable.
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