[edit] Mirror neurons and vocal learning

A mirror neuron is a neuron that discharges both when an individual performs an action, and when he perceives that same action being performed by another.^[63] These neurons were first discovered in macaque monkeys, but recent research suggests that mirror neuron systems may be present in other animals including humans.^[64]

Mirror neurons have the following characteristics:^[63]

• They are located the premotor cortex
• They exhibit both sensory and motor properties
• They are action-specific – mirror neurons are only active when an individual is performing or observing a certain type of action (e.g.: grasping an object).

Because mirror neurons exhibit both sensory and motor activity, some researchers have suggested that mirror neurons may serve to map sensory experience onto motor structures.^[65] This has implications for birdsong learning– many birds rely on auditory feedback to acquire and maintain their songs. Mirror neurons may be mediating this comparison of what the bird hears and what he produces.

Song selectivity in HVCx neurons: neuron activity in response to calls heard (green) and calls produced (red). a. Neurons fire when the primary song type is either heard or sung. b,c. Neurons do not fire in response to the other song type, regardless of whether it is heard or sung. Sketch based on figure from Prather et al. (2008)

In search of these auditory-motor neurons, Jonathan Prather and other researchers at Duke University recorded the activity of single neurons in the HVCs of swamp sparrows.^[66] They discovered that the neurons that project from the HVC to Area X (HVC_X neurons) are highly responsive when the bird is hearing a playback of his own song. These neurons also fire in similar patterns when the bird is singing that same song. Swamp sparrows employ 3-5 different song types, and the neural activity differs depending on which song is heard or sung. The HVC_X neurons only fire in response to the presentation (or singing) of one of the songs, the primary song type. They are also temporally selective, firing at a precise phase in the song syllable.

Because the timing of the neural response is identical regardless of whether the bird was listening or singing, how can we be sure that the bird isn’t just hearing himself? Prather et al. found that during the short period of time before and after the bird sings, his HVC_X neurons become insensitive to auditory input. In other words, the bird becomes "deaf" to his own song. This suggests that these neurons are producing a corollary discharge, which would allow for direct comparison of motor output and auditory input.^[67] This may be the mechanism underlying learning via auditory feedback.

Overall, the HVC_X auditory-motor neurons in swamp sparrows are very similar to the visual-motor mirror neurons discovered in primates. Like mirror neurons, the HVC_X neurons:

• Are located in a premotor brain area
• Exhibit both sensory and motor properties
• Are action-specific – a response is only triggered by the ‘primary song type’

The function of the mirror neuron system is still unclear. Some scientists speculate that mirror neurons may play a role in understanding the actions of others, imitation, theory of mind and language acquisition, though there is currently insufficient neurophysiological evidence in support of these theories.^[65] Specifically regarding birds, it is possible that the mirror neuron system serves as a general mechanism underlying vocal learning, but further research is needed. In addition to the implications for song learning, the mirror neuron system could also play a role in territorial behaviors such as song-type matching and countersinging.^[68]

[edit] Identification and systematics

Song of the White-throated Sparrow

The specificity of bird calls has been used extensively for species identification. The calls of birds have been described using words or nonsense syllables, or line diagrams.^[69] Common terms in English include words such as quack, chirp and chirrup. These are subject to imagination and vary greatly; a well-known example is the White-throated Sparrow's song, given in Canada as O sweet Canada Canada Canada and in New England as Old Sam Peabody Peabody Peabody (also Where are you Frederick Frederick Frederick?). In addition to nonsense words, grammatically correct phrases have been constructed as likenesses of the vocalizations of birds. For example, the Barred Owl produces a motif which some bird guides describe as Who cooks for you? Who cooks for you all? with the emphasis placed on you.^[70]

Sonogram of the call of a Laughing Dove. Recorded in south India (help·info)

The use of spectrograms to visualize bird song was first introduced by W. H. Thorpe.^[71][72] These visual representations are also called sonograms or sonagrams. Some recent field guides for birds use sonograms to document the calls and songs of birds.^[73] The sonogram is objective, unlike descriptive phrases, but proper interpretation requires experience. Sonograms can also be roughly converted back into sound.^[74][75]
Bird song is an integral part of bird courtship and is a pre-zygotic isolation mechanism involved in the process of speciation. Many allopatric sub-species show differences in calls. These differences are sometimes minute, often detectable only in the sonograms. Song differences in addition to other taxonomic attributes have been used in the identification of new species.^[76] The use of calls has led to proposals for splitting of species complexes such as those of the Mirafra Bushlarks.^[77]

[edit] Bird song and music

Some musicologists believe that birdsong has had a large influence on the development of music.^[78] Although the extent of this influence is impossible to gauge,^[79] it is sometimes easy to see some of the specific ways composers have integrated birdsong with music.
There seem to be three general ways musicians or composers can be affected by birdsong: they can be influenced or inspired (consciously or unconsciously) by birdsong, they can include intentional imitations of bird song in a composition, or they can incorporate recordings of birds into their works.
One early example of a composition that imitates birdsong is Janequin's "Le Chant Des Oiseaux", written in the 16th century. Other composers who have quoted birds or have used birdsong as a compositional springboard include Vivaldi (Spring from the Four Seasons)), Biber (Sonata Representativa), Beethoven (Sixth Symphony), Wagner (Siegfried) and the jazz musicians Paul Winter (Flyway) and Jeff Silverbush (Grandma Mickey).^[80]
The twentieth-century French composer Olivier Messiaen composed with birdsong extensively. His Catalogue d'Oiseaux is a seven-book set of solo piano pieces based upon birdsong. His orchestral piece Réveil des Oiseaux is composed almost entirely of birdsong. Many of his other compositions, including Quatuor pour la fin du temps, similarly integrate birdsong.^[81]
The Italian composer Ottorino Respighi, with his The Pines of Rome (1923–1924), may have been the first to compose a piece of music that calls for pre-recorded birdsong. A few years later, Respighi wrote Gli Uccelli ("The birds"), based on Baroque pieces imitating birds.
The Finnish composer Einojuhani Rautavaara in 1972 wrote an orchestral piece of music called Cantus Arcticus (Opus 61, dubbed Concerto for Birds and Orchestra) making extensive use of pre-recorded birdsongs from Arctic regions, such as migrating swans.
The American jazz musician Eric Dolphy sometimes listened to birds while he practiced flute. He claimed to have incorporated bird song into some of his improvisational music.
In the psychedelic era of the 1960s and 1970s, many rock bands included sound effects in their recordings. Birds were a popular choice. The English band Pink Floyd included bird sound effects in many of the songs from their 1969 albums Soundtrack from the Film More and Ummagumma (for example, Grantchester Meadows). Similarly, the English singer Kate Bush incorporated bird sound effects into much of the music on her 2005 album, Aerial.
The Music hall artist Ronnie Ronalde has gained notoriety for his whistling imitations of birds and for integrating birdsong with human song. His songs 'In A Monastery Garden' and 'If I Were A Blackbird' include imitations of the blackbird, his "signature bird."^{[citation needed]}
The French composer François-Bernard Mâche has been credited with the creation of zoomusicology, the study of the music of animals. His essay Musique, mythe, nature, ou les Dauphins d'Arion (1983) includes a study of "ornitho-musicology", in which he speaks of "animal musics" and a longing to connect with nature.
The German DJ, techno music producer and naturalist Dominik Eulberg is an avid bird watcher, and several tracks by him prominently feature sampled bird sounds and even are titled after his favourite specimens.^{[citation needed]}
The productions of The Jewelled Antler Collective often use field recordings featuring birdsong.
In 2007, The CT Collective issed two free albums devoted to music made using bird songs (one with human interaction, one without). The project was co-ordinated by looping musician Nick Robinson

[edit] Bird song and poetry

Bird song is a popular subject in poetry. Famous poems inspired by bird song include Percy Bysshe Shelley's To a Skylark ("Hail to thee, blithe Spirit!/Bird thou never wert") and Gerard Manley Hopkins' Sea and Skylark. Birdsongs and their relations to Middle-earth inhabitants are a common motif in J. R. R. Tolkien's literary work.^{[citation needed]} The Grateful Dead performed a song called "Bird Song" that Jerry Garcia wrote and dedicated to Janis Joplin.