Bird vocalization includes both
bird calls and bird songs. In non-technical use, bird
songs 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'.
Definition
The distinction between songs and calls is based upon inflection,
length, and context. 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 short
vocalizations 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 are nearly
voiceless, producing only
percussive and
rhythmic sounds, such as the
storks, which clatter their bills. In some manakins
(
Pipridae), the males have evolved several
mechanisms for mechanical sound production, including mechanisms
for
stridulation not unlike those found
in some insects.
The production of sounds by mechanical means as opposed to the use
of the
syrinx has been termed
variously
instrumental music by
Charles Darwin,
mechanical sounds
and more recently
sonation. The term
sonate has
been defined as the act of producing non-vocal sounds that are
intentionally modulated communicative signals, produced using
non-syringeal structures such as the bill, wings, tail, feet and
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 sound waves that are made by
membranes past which the bird forces air. The bird controls the
pitch by changing the tension on the membranes and controls both
pitch and volume by changing the force of exhalation. It 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, which 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.
Mobbing calls are 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 which are common
across species and are believed to be helpful to other potential
"mobbers" by being easy to locate. The alarm calls of most species,
on the other hand, are characteristically high-pitched making the
caller difficult to locate.
Individual birds may be sensitive enough to identify each other
through their calls. Many birds that nest in colonies can 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 so
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,
bushshrikes,
babbler such as the
scimitar babblers, some owls and parrots.
In territorial songbirds, birds are more likely to countersing when
they have been aroused by simulated intrusion into their territory.
This implies a role in intraspecies aggressive competition.
Some birds are excellent vocal
mimics. In
some tropical species, mimics such as the
drongos may have a role in the formation of
mixed-species foraging flocks.
Vocal mimicry can include conspecifics, other species or even
man-made sounds. Many hypotheses have been made on the functions of
vocal mimicry including suggestions that they may be involved in
sexual selection by acting as an indicator of fitness, help brood
parasites, protect against predation but strong support is lacking
for any function. Many birds, and especially those that nest in
cavities, are known to produce a snake like hissing sound that may
help deter predators at close range.
Some cave-dwelling species, including
Oilbird and Swiftlets (
Collocalia and
Aerodramus spp.), use audible sound (with
the majority of sonic location occurring between 2 and 5 kHz)
to
echolocate in the darkness of
caves.
The hearing range of birds is from below 50 Hz (infrasound) to
above 20 kHz (ultrasound) with maximum sensitivity between 1
and 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, and 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), and 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". Birds sing louder and at a higher pitch in urban areas, where there is ambient low-frequency noise.
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 is claimed to
demonstrate the innate ability for grammatical structures,
including the existence of concepts such as nouns, adjectives and
verbs. Studies on
starling vocalizations
have also suggested that they may have recursive structures.
Those who set forth the existence of bird language in
tracking and
naturalist studies denote 5 basic types of sound:
call, song, territorial, fledgling, and alarm. The first four are
denoted as "baseline" behavior, relating to the relative safety and
calm of the birds, while the later denotes the awareness of a
threat or predator. Within each of these basic categories, the
particular of meanings of these sounds are based upon inflection,
body language and contextual setting.
Neurophysiology
The main brain areas involved in bird song are:
- Anterior forebrain pathway (vocal
learning): composed of the lateral part of the magnocellular nucleus of
anterior neostriatum (LMAN), which is a homologue to mammalian
basal ganglia); Area X, which is part
of the basal ganglia; and the Dorso-Lateral division of the Medial
thalamus (DLM).
- Song production pathway: composed of the HVC (sometimes, inaccurately, called the
Hyperstriatum Ventralis pars Caudalis); robust nucleus of the
arcopallium (RA); and the tracheosyringeal part of the hypoglossal
nucleus (nXIIts).
Both pathways show
sexual
dimorphism, with the male producing song most of the time. It
has been noted that injecting
testosterone in non-singing female birds can
induce growth of the HVC and thus production of song.
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.
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, LMAN and the ventrolateral medulla. Other researchers
have explored the possibility that
HVc 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.
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 does not pass for another
species). As early as 1773 it was established that birds learnt
calls and
cross-fostering
experiments were able to force a Linnet
Acanthis cannabina
to learn the song of a skylark
Alauda arvensis. In many
species it appears that although the basic song is the same for all
members of the species, young birds learn some details of their
songs from their fathers, and these variations build up over
generations to form
dialects.
Birds learn songs early in life with sub-vocalizations that develop
into renditions of adult songs.
Zebra
Finches, the most popular species for 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" or variable and it takes
the young bird two or three months to perfect the "crystallized"
song (which is less variable) of sexually mature birds.
Timeline for song learning in
different species.
Diagram adapted from Brainard & Doupe, 2002..
Research indicates birds' acquisition of song is a form of
motor learning that involves regions of the
basal ganglia. Models of bird-song
motor learning are sometimes used as models for how humans learn
speech. In some species such as zebra finches, learning of song is
limited to the first year; they are termed 'age-limited' or
'close-ended' learners. Other species such as the
canaries can develop new songs even as sexually
mature adults; these are termed 'open-ended' learners.
Researchers have hypothesized that 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.
Auditory feedback in bird song learning
Early experiments by
Thorpe in
1954 showed the importance of a bird being able to hear a tutor's
song. When birds are raised in isolation, away from the influence
of
conspecific males, they still sing.
While the song they produce resembles the song of a wild bird, it
lacks the complexity and sounds distinctly different. The
importance of the bird being able to hear himself sing in the
sensorimotor period
was later discovered by Konishi. Birds deafened before the song
crystallization period went on to produce very different songs from
the
wild type. These findings lead
scientists to believe there could be a specific part of the brain
dedicated to this specific type of learning.
Song learning pathway in birds (Based
on Nottebohm, 2005)
The main focus in the search for the neuronal aspect of bird song
learning was guided by the song template hypothesis. This
hypothesis is the idea that when a bird is young he memorizes the
song of his tutor. Later, during the development phase as an adult,
he matches his own trial vocalizations using auditory feedback to
an acoustic template in the brain. Based on this information, he
adjusts his song if needed. To find this "song template,"
experimenters
lesioned certain parts of the
brain and observed the effects.
- Lesioning the song
production pathway (RA, xXII or HVc) in the brain creates
serious effects on song production in all birds.
- Lesions parts of the anterior forebrain pathway, or
vocal learning pathway, DLM and area X, result in deficits in
learning in all birds.
- Lesioning LMAN, located in the anterior forebrain pathway in
young birds disrupts song production.
- Lesioning LMAN on an adult bird shows no effect.
- Lesioning LMAN on an adult canary (an "open-ended learner" species, which can
learn songs later in life) shows a progressive deterioration of
song.
These results show that the area known as LMAN is the only brain
area in the pathway that shows some
plasticity and further studies have shown
that this area of the brain responds best to the bird's own song.
This neuroplasticity is vital for a bird being able to learn a
song. The ability to make small adjustments based on auditory
feedback is needed for the complexity of these beautiful songs.
Just like any musician, birds need to practice and be able to
evaluate what their song sounds like and what it's supposed to
sound like in order to get it right.
To complete the picture on bird song learning, experimenters needed
to discover the true plasticity of the brain. While deafening and
creating auditory isolation were good techniques for discovering
basic characteristics about the brain, a reversible procedure was
needed to investigate further. The solution was found in disruption
of the auditory feedback, or what a bird hears. A computer is able
to capture the song of a singing bird and play back portions of its
song, or selectively play back a certain syllable while the bird is
singing. The computer is basically playing the age old trick of
repeating whatever the bird sings, the "stop copying me" game. This
creates such a disruption that an adult bird will start to
decrystallize its song, which includes a loss of
spectral and temporal rigidity characteristic
of adult song. It reverts back to the song it started singing with,
before any learning took place. Furthermore, when the feedback was
stopped, the birds slowly recovered their original song, something
that was unheard of. These results show that there is a fair amount
of plasticity retained in the brain, even for close-ended learners.
This new found plasticity in adult birds and the results on the
plasticity of LMAN (shown above) combine into a model for bird song
learning (diagram coming soon).
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, or line diagrams.. 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.
The use of
spectrograms to visualize
bird song was first introduced by W. H. Thorpe. 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. 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, often
detectable 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 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).
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.
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."
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.
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
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.
The Grateful Dead performed a song called
"Bird Song" that
Jerry Garcia wrote and
dedicated to
Janis Joplin.
See also
Cited reference
- Manson-Barr, P. and Pye, J. D. (1985). Mechanical sounds. In A
Dictionary of Birds (ed. B. Campbell and E. Lack), pp. 342-344.
Staffordshire: Poyser.
- Saunders, Aretas A (1951) Guide to Bird Songs. Doubleday and
Company
- US Patent. 20030216649. Audible output sonogram
analyzer
- Jeff Silverbush
- Griffiths, A Technique for the End of Time (1985)
External links
distributes a number of different free bird song
synthesis & analysis programs.
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