Song in Birds

Sound perception and production in birds, especially oscines, has been the subject of much research. Birds’ singing and song learning systems have been studied from perspectives ranging from mechanical through neurological to social and adaptive. Mechanically speaking, birds produce song via the syrinx, an analog to the human larynx. Found at the entrance of the bronchioles, the syrinx is a group of connective tissues, cartilage rings, and membranes that vibrate in concert to produce sound. Sound itself comes not from the vibration of the medial tympaniform membranes but from connective tissue at the end of each bronchus that sticks into the syringeal lumen. From a neurological point of view, bird song perception, production, and learning originates in a series of neuronal nuclei heretofore referred to as the song pathway. Perception of song begins in auditory field L in conjunction with the NCM and CMM areas. These signals are then passed through the HVC, area X, LMAN, and DLM which all have song selective neurons that discriminate between different song types. Song production also comes from the song pathway and uses the same nuclei. Firstly, main auditory field L projects to both the HVC and RA, and the HVC itself projects to the RA. Secondly, from the RA is a projection to nXIIts, from which there is direct innervation of the syrinx, and thus, song production. Song learning also takes place in the song pathway, though this is less well understood and seems to have to do with the expression of immediate early genes (IEGs) such as ZENK in different neuronal nuclei depending on the acoustic environment.