Passerine birds A passerine () is any bird of the order Passeriformes (; from Latin 'sparrow' and '-shaped') which includes more than half of all bird species. Sometimes known as perching birds, passerines generally have an anisodactyl arrangement of their ...

produce song through the vocal organ, the

syrinx In classical Greek mythology, Syrinx () was an Arcadian nymph and a follower of Artemis, known for her chastity. Being pursued by Pan, she fled into the river Ladon, and at her own request was metamorphosed into a reed from which Pan then mad ...

, which is composed of bilaterally symmetric halves located where the

trachea The trachea (: tracheae or tracheas), also known as the windpipe, is a cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all animals' lungs. The trachea extends from ...

separates into the two

bronchi A bronchus ( ; : bronchi, ) is a passage or airway in the lower respiratory tract that conducts air into the lungs. The first or primary bronchi to branch from the trachea at the carina are the right main bronchus and the left main bronchus. Thes ...

. Using

endoscopic An endoscopy is a procedure used in medicine to look inside the body. The endoscopy procedure uses an endoscope to examine the interior of a hollow organ or cavity of the body. Unlike many other medical imaging techniques, endoscopes are insert ...

techniques, it has been observed that song is produced by air passing between a set of medial and lateral labia on each side of the syrinx. Song is produced bilaterally, in both halves, through each separate set of labia unless air is prevented from flowing through one side of the syrinx. Birds regulate the airflow through the syrinx with

muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

s—M. syringealis dorsalis and M. tracheobronchialis dorsalis—that control the

medial Medial may refer to: Mathematics * Medial magma, a mathematical identity in algebra Geometry * Medial axis, in geometry the set of all points having more than one closest point on an object's boundary * Medial graph, another graph that repr ...

and

lateral Lateral is a geometric term of location which may also refer to: Biology and healthcare * Lateral (anatomy), a term of location meaning "towards the side" * Lateral cricoarytenoid muscle, an intrinsic muscle of the larynx * Lateral release ( ...

labia in the syrinx, whose action may close off airflow. Song may, hence, be produced

unilaterally __NOTOC__ Unilateralism is any doctrine or agenda that supports one-sided action. Such action may be in disregard for other parties, or as an expression of a commitment toward a direction which other parties may find disagreeable. As a word, ''un ...

through one side of the syrinx when the labia are closed in the opposite side.

Early experiments discover lateralization

Lateral dominance of the

hypoglossal nerve The hypoglossal nerve, also known as the twelfth cranial nerve, cranial nerve XII, or simply CN XII, is a cranial nerve that innervates all the extrinsic and intrinsic muscles of the tongue except for the palatoglossus, which is innervated b ...

conveying messages from the

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

to the syrinx was first observed in the 1970s. This lateral dominance was determined in a breed of canary, the waterschlager canary, bred for its long and complex song, by

lesion A lesion is any damage or abnormal change in the tissue of an organism, usually caused by injury or diseases. The term ''Lesion'' is derived from the Latin meaning "injury". Lesions may occur in both plants and animals. Types There is no de ...

ing the ipsilateral tracheosyringeal branch of the hypoglossal nerve, disabling either the left or right syrinx. The numbers of song elements in the birds’ repertoires were greatly attenuated when the left side was cut, but only modestly attenuated when the right side was disabled, indicating left syringeal dominance of song production in these canaries. Similar lateralized effects have been observed in other species such as the

white-crowned sparrow The white-crowned sparrow (''Zonotrichia leucophrys'') is a species of passerine bird native to North America. A medium-sized member of the New World sparrow family, this species is marked by a grey face and black and white streaking on the upp ...

(Zonotrichia leucophrys), the

Java sparrow The Java sparrow (''Padda oryzivora''; Japanese: 文鳥, ''bunchō''), also known as the Java finch, Java rice sparrow or Java rice bird, is a small passerine bird. This estrildid finch is a resident breeding bird in Java, Bali and Bawean in In ...

(Lonchura oryzivora) and the

zebra finch The zebra finches are two species of estrildid finch in the genus ''Taeniopygia'' found in Australia and Indonesia. They are seed-eaters that travel in large flocks. Species The species are: Previously, both species were classified as ...

(''Taeniopygia guttata''), which is right-side dominant. However, denervation in these birds does not entirely silence the affected syllables but creates qualitative changes in

phonology Phonology (formerly also phonemics or phonematics: "phonemics ''n.'' 'obsolescent''1. Any procedure for identifying the phonemes of a language from a corpus of data. 2. (formerly also phonematics) A former synonym for phonology, often pre ...

and

frequency Frequency is the number of occurrences of a repeating event per unit of time. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio ...

Respiratory control and neurophysiology

In waterslager canaries, which produce most syllables using the left syrinx, as soon as a unilaterally produced syllable finishes, the right side opens briefly to allow inspiratory airflow through both bronchi before being closed again for left syrinx song production. During this “mini-breath” the left side may remain partially or fully adducted, allowing less inspiratory airflow than the right side while remaining ready to quickly resume singing. When bilateral airflow and subsyringeal air sac pressure were monitored along with

electromyographic Electromyography (EMG) is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph to produce a record called an electromyogram. An electromyog ...

activity of expiratory

abdominal The abdomen (colloquially called the gut, belly, tummy, midriff, tucky, or stomach) is the front part of the torso between the thorax (chest) and pelvis in humans and in other vertebrates. The area occupied by the abdomen is called the abdominal ...

muscles in

brown thrasher The brown thrasher (''Toxostoma rufum''), sometimes erroneously called the brown thrush or fox-coloured thrush, is a bird in the family Mimidae, which also includes the Catbird, New World catbirds and mockingbirds. The brown thrasher is abundant ...

s (''Toxostoma rufum)'', it was observed that during unilateral production of song, expiratory abdominal muscle activity was the same on both sides. This indicates that while inspiration and syringeal song control may be lateralized,

motor control Motor control is the regulation of movements in organisms that possess a nervous system. Motor control includes conscious voluntary movements, subconscious muscle memory and involuntary reflexes, as well as instinctual taxes. To control ...

respiratory The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies gr ...

muscles possibly remains bilateral. Muscles of the syrinx are controlled by the tracheosyringeal branch of the

. Each syringeal half is ipsilaterally innervated by the hypoglossal motor nucleus (XIIts) in the brain, which in turn receives projections—mainly ipsilateral—from nucleus robustus (RA), an important song control nucleus that also regulates respiratory muscles. Laterality of song control has been observed all the way into the higher vocal center (HVC) brain region; unilateral lesions to HVC produce lateralized effects in the temporal patterning of song in the zebra finch. See also Bird song: Neuroanatomy

Species-specific examples

Canary (''Serinus canaria'')

The waterschlager canary is the most robust example of unilateral syringeal dominance, creating song of which 90% of the syllables are produced by the left syrinx, as determined by recording respiratory pressure and airflow through each side during singing. Waterschlager canaries with left tracheosyringeal nerve cuts are only able to produce up to 26% of the pre-operation syllable repertoire. The waterschlager canary strain is conspecific to the

domestic canary The domestic canary (''Serinus canaria'' forma ''domestica''), often simply known as the canary, is a domesticated form of the wild canary, a small songbird in the finch family originating in the Macaronesian Islands. Over the past 500 years ...

but has been inbred by humans for its beautiful song. The outbred domestic canary, however, does not exhibit the strong lateralization of the waterschlager canary. Possibly explaining their strong left lateralization, canaries of the waterschlager strain contain an inherited auditory defect that decreases their sensitivity by up to 40 dB to sounds higher than 2 kHz, which are produced mainly by the right side of the syrinx.

Brown-headed cowbird (''Molothrus ater'')

The

brown-headed cowbird The brown-headed cowbird (''Molothrus ater'') is a small, obligate brood parasitic icterid native to temperate and subtropical North America. It is a permanent resident in the southern parts of its range; northern birds migrate to the souther ...

produces very rapid clusters of notes that alternate in frequency, with the right syrinx producing the high frequency notes and the left syrinx producing low frequency notes. The entire cluster is sung during a single respiratory expiration, called "pulsatile expiration", in which no inflow of air occurs between notes. By alternating note production successively between each side of the syrinx and without ceasing expiration, a cowbird is able to rapidly and abruptly switch the frequency of notes back and forth between high and low frequencies. To see a cartoon of how syllables are produced in alternate sides of the syrinx
click here

Northern cardinal (''Cardinalis cardinalis'')

Northern cardinal The northern cardinal (''Cardinalis cardinalis''), also commonly known as the common cardinal, red cardinal, or simply cardinal, is a bird in the genus ''Cardinalis''. It can be found in southeastern Canada, through the eastern United States fro ...

s contain FM sweep syllables as part of their repertoire that begin around 6 or 7 kHz and sweep downward continuously to 2

kHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose formal expression in terms of SI base uni ...

. Each of these syllables is sung unilaterally. However, the cardinal switches mid-syllable from employing the right syrinx at the high frequency beginning of the sweep to the left syrinx at the lower frequency end. This switch usually occurs when the sweep reaches the 3.5 to 4.0 kHz range. The transition is abrupt yet timed so precisely that neither sonograms nor

audition An audition is a sample performance by an actor, singer, musician, dancer or other performer. It typically involves the performer displaying their talent through a previously memorized and rehearsed solo piece or by performing a work or piece gi ...

can detect the switch. To see a cartoon of how the syrinx produces cardinal song
click here

Northern mockingbird (''Mimus polyglottus'')

Because the

mockingbird Mockingbirds are a group of New World passerine birds from the family (biology), family Mimidae. They are best known for the habit of some species Mimicry, mimicking the songs of other birds and the sounds of insects and amphibians, often loudly ...

has the ability to mimic the songs of other species, it has been useful in determining whether the vocal motor patterns employed by particular species in producing their unique song types are constrained by acoustic properties or whether the unique song types may also be produced by different motor patterns generated by the same songbird vocal system. When juvenile mockingbirds were tutored with the recorded or synthesized song of a cardinal or cowbird, the mockingbirds employed the same respiratory and lateralized vocal pattern as the original species to produce its mimicked song. When the mockingbird motor pattern differed from the tutor motor pattern, the song output also differed, suggesting that the vocal motor pattern is largely determined by the acoustic restraints of the song type. Even though the mockingbird was able to mimic the FM sweeps of cardinals by employing the same motor pattern—switching mid-syllable from right syrinx to left syrinx—the mockingbird did not perform the transition seamlessly. This indicates that precise unilateral control of song production in the syrinx of certain birds, such as cardinals, has allowed them to become unique vocal specialists.

Possible functions

Because the lateralized control of songs of certain species, such as cardinals, demands such precision in motor control, the ability to produce high-quality, seamless syllables may provide an indicator of fitness to potential mates. Supporting this

hypothesis A hypothesis (: hypotheses) is a proposed explanation for a phenomenon. A scientific hypothesis must be based on observations and make a testable and reproducible prediction about reality, in a process beginning with an educated guess o ...

, certain syllables called "sexy syllables" sung by male canaries at high frequency are more effective than others in eliciting

sexual display A courtship display is a set of display behaviors in which an animal, usually a male, attempts to attract a mate; the mate exercises choice, so sexual selection acts on the display. These behaviors often include ritualized movement ("dances"), ...

s from females. These particular syllables all contain two notes that are sung alternately by each side of the syrinx. Thus, control of the rapid switching from one side of the syrinx to the other is required to produce these attractive syllables. Lateralization also allows for rapid and abrupt frequency changes. Studies of mockingbirds mimicking

tone Tone may refer to: Visual arts and color-related * Tone (color theory), a mix of tint and shade, in painting and color theory * Tone (color), the lightness or brightness (as well as darkness) of a color * Toning (coin), color change in coins * ...

pairs in which the first tone was either higher or lower than a median tone of 2 kHz (either side is capable of producing this median tone) revealed that alternating sides of the syrinx for each note was necessary to reproduce them correctly. Correct mimicking was performed by singing the first syllable with the appropriate side of the syrinx—right for a high frequency tone and left for low frequency—and the second median tone with the opposite side. When the same side was used for both tones, the step-wise frequency change between the tones became slurred, suggesting that lateralization allows for abrupt frequency changes in song.

References

External links

X-ray video of a cardinal singing

Macaulay Library
at the

Cornell Lab of Ornithology The Cornell Lab of Ornithology is a member-supported unit of Cornell University in Ithaca, New York, which studies birds and other wildlife. It is housed in the Imogene Powers Johnson Center for Birds and Biodiversity in Sapsucker Woods Sanctuar ...

is the world's largest collection of animal sounds and associated video.
xeno-canto
a community database with c. 183,000 recordings of c. 9,000 bird species (August 2014) {{DEFAULTSORT:Lateralization Of Bird Song Neuroethology Bird sounds Passeri