Bird song



Bird songs are certain vocal sounds that birds make. In non-technical use, these are the bird sounds that are melodious to the human ear. In ornithology, bird 'songs' are often distinguished from shorter sounds, which may be termed 'calls'. The term is used here to cover bird vocalization in all its forms.

Definition
The distinction between songs and calls is somewhat arbitrary. Songs are longer and more complex and are associated with courtship and mating, while calls tend to serve such functions as alarms or keeping members of a flock in contact. Other authorities such as Howell and Webb (1995) make the distinction based on function, so that even short vocalisations such as those of pigeons and even non-vocal sounds such as the drumming of woodpeckers and the "winnowing" of snipes' wings in display flight are considered songs. Still others require song to have syllabic diversity and temporal regularity akin to the repetitive and transformative patterns which define music.

Bird song is best developed in the order Passeriformes. Most song is emitted by male rather than female birds. Song is usually delivered from prominent perches although some species may sing when flying. Some groups such as the Storks are nearly voiceless with the only sounds produced mechanically by bill-clattering. In some members of the Manakins, Pipridae the males have evolved several mechanisms for mechanical sound production including mechanisms for stridulation not unlike those in the insects.

The production of sounds by mechanical means as opposed to those made using the syrinx have been termed variously in the past as instrumental music by Charles Darwin, mechanical sounds and more recently as sonation. The term sonate has been defined as the act of producing non-vocal acoustic signals that are intentionally modulated, communicative acoustic signals, produced using non-syringeal structures such as the bill, wings, tail, feet and/or body feathers.

Anatomy
The avian vocal organ is called the syrinx; it is a bony structure at the bottom of the trachea (unlike the larynx at the top of the mammalian trachea). The syrinx and sometimes a surrounding air sac resonate to vibrations that are made by membranes past which the bird forces air. It controls the pitch by changing the tension on the membranes and controls both pitch and volume by changing the force of exhalation. The bird can control the two sides of the trachea independently, which is how some species can produce two notes at once.

Function
Scientists hypothesize that bird song has evolved through sexual selection and experiments suggest that the quality of bird song may be a good indicator of fitness. Experiments also suggest that parasites and diseases may directly affect song characteristics such as song rate and thereby act as reliable indicators of health. The song repertoire also appears to indicate fitness in some species. The ability of male birds to hold and advertise territories using song also demonstrates their fitness.

Communication through bird calls can be between individuals of the same species or even across species. The mobbing calls of birds used to recruit individuals in an area where an owl or other predator may be present. These calls are characterized by wide frequency-spectra, sharp onset and termination, and repetitiveness. These characteristics are common across species and are believed to be helpful to other potential mobbers, in being easy to locate. The alarm calls of many species, on the other hand, are characteristically high pitched and difficult to locate.

Individual birds may be sensitive enough to identify each other through their calls. Many birds that nest in colonies are able to locate their chicks using their calls. Calls are sometimes distinctive enough for individual identification even by human researchers in ecological studies.

Many birds engage in duet calls. In some cases the duets are perfectly timed as to appear almost as one call. This kind of calling is termed antiphonal duetting. Such duetting is noted in a wide range of families including quails, babblers such as the Scimitar babblers, some owls and parrots. The function of such orchestrated calling is unclear.

Some birds are excellent mimics. In some tropical species it has been hypothesized that mimics such as the drongo may have a role in the formation of mixed species foraging flocks.

Some cave-dwelling species, including Oilbird and Swiftlets (Collocalia and Aerodramus spp.), use ultrasound to echolocate in the darkness of caves.

The bird hearing range starts below 50 Hz (infrasound) to above 20 kHz (ultrasound) with maximum sensitivity between 1-5 kHz. The range of frequencies at which birds call in an environment varies with the quality of habitat and the ambient sounds. It has been suggested that narrow bandwidths, low frequencies, low frequency modulations, long elements and inter-element intervals should be found in habitats with complex vegetation structures (which would absorb and muffle sounds) while high frequencies, broad bandwidth, high frequency modulations (trills), short elements and inter-elements may be expected in habitats with herbaceous cover. It has been hypothesized that the available frequency range is partitioned and birds call so that overlap between different species in frequency and time is reduced. This idea has been termed the "acoustic niche". In urban areas with a lot of low frequency noise, it has been noted that birds sing louder as well as at a higher pitch.

Language
The language of the birds has long been a topic for anecdote and speculation. That calls have meanings that are interpreted by their listeners has been well demonstrated. Domestic chicken have distinctive alarm calls for aerial and ground predators and they respond to these alarm calls appropriately. However a language has in addition to words, structures and rules. Studies to demonstrate the existence of language have been difficult due to the range of possible interpretations. Research on parrots by Irene Pepperberg demonstrates the innate ability for grammatical structures including the existence of concepts such nouns, adjectives and verbs.

Learning
The songs of different species of birds vary, and are more or less characteristic of the species. In modern-day biology, bird song is typically analysed using acoustic spectroscopy. Species vary greatly in the complexity of their songs and in the number of distinct kinds of song they sing (up to 3000 in the Brown Thrasher); in some species, individuals vary in the same way. In a few species such as starlings and mockingbirds, songs imbed arbitrary elements learned in the individual's lifetime, a form of mimicry (though maybe better called "appropriation" [Ehrlich et al.], as the bird doesn't pass for another species). 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.

Birds learn songs early in life with sub-vocalizations that develop into renditions of adult songs. Zebra Finches, the most popular species 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. The early song is "plastic" and variable and it takes two or three months to and the song is perfect and non-varying when the bird becomes sexually mature.

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. In some species such as zebra finches learning of song is limited to the first year and they are termed as 'age-limited' or 'close-ended' learners. Other species such as the canaries can develop new songs even as sexually mature adults and these are termed as 'open-ended' learners.

Researchers have hypothesized learned songs allow the development of more complex songs through cultural interaction, thus allowing intraspecies dialects that help birds stay with their own kind within a species, and it allows birds to adapt their songs to different acoustic environments.

Neurophysiology
A bird that has been deafened at birth is able to sing, but the song is made up of disjointed notes.

Birdsong learning seems to occur somewhere along a set of discrete but interconnected nuclei, collectively called the song system. In most birds, the male sings and it has been noted that injecting testosterone in female birds can initiate development of the vocal control nuclei and singing. Many researchers believe that the high vocal center, the robust nucleus of the acropallium (RA), and the nucleus Area X may all play key roles. Area X is particularly interesting, as lesions in adult brains have limited effect on song, while lesions during the period of song learning (the critical period) have drastic effects.

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 nidopallium to the HVC, and then to RA, the dorso-lateral division of the medial thalamus and to the tracheosyringeal nerve.

Disruptions along the learning pathway (including Area X) between 20 and 60 days of a finch's life (the critical period) permanently damages the bird's song, but has no effect if the same pathways were disrupted later in life. Disruptions along the production pathways can always damage a bird's ability to sing. Interestingly, the gene FOXP2, defects of which affect both speech and comprehension of language in humans, becomes more active in the striatal region of songbirds during the time of song learning.

Recent research in birdsong learning has focused on the Ventral Tegmental Area (VTA), which sends a dopamine input to the para-olfactory lobe and Area X, the lateral magnocellular nucleus of the anterior nidopallium (lMAN) 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 arcopallium, the primary song output nucleus, may be responsible for syllable sequencing and production of notes within a syllable.

Identification and systematics
The specificity of bird calls has been used extensively for species identification. The calls of birds have been described using words or nonsense syllables. 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.'' More recent field guides for birds use sonograms to define the calls and songs of birds. The sonogram is objective unlike descriptive phrases but proper interpretation requires experience. Sonograms can also be roughly converted back into sound.

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 and are often visible only in the sonograms. Song differences in addition to other taxonomic attributes have been used in the identification of new species. The use of calls has led to proposals for splitting of species complexes such as those of the Mirafra Bushlarks.

Bird song and music
Some musicologists believe that birdsong has had a large influence on the development of music. Although the extent of this influence is impossible to gauge, 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 who have used birdsong as a compositional springboard, include Biber (Sonata Representativa), Beethoven (Sixth Symphony), Wagner (Siegfried) and jazz musicians Paul Winter (Flyway) and Jeff Silverbush (Grandma Mickey).

Twentieth century French composer Olivier Messiaen deserves special mention, as he 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.

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 the addition of pre-recorded birdsong. A few years later, Respighi wrote Gli Uccelli ("The birds"), based on Baroque pieces imitating birds.

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.

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 1970's, 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 More and Ummagumma (see, for example Grantchester Meadows). Similarly, the English singer Kate Bush incorporated bird sound effects into much of the music on her 2005 album, Aerial.

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."

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.

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. Much of Tolkien's work is centered around birdsong and its relation to Middle-earth inhabitants.