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 and birding, songs (relatively complex vocalizations) are distinguished by function from calls (relatively simple vocalizations).
The distinction between songs and calls is based upon complexity, length, and context. Songs are longer and more complex and are associated with territory  and 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 that define music. It is generally agreed upon in birding and ornithology which sounds are songs and which are calls, and a good field guide will differentiate between the two.
Bird song is best developed in the order Passeriformes. 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. 
Song is usually delivered from prominent perches, although some species may sing when flying. 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. 
In extratropical Eurasia and the Americas almost all song is produced by male birds; however in the tropics and to a greater extent the desert belts of Australia and Africa it is more typical for females to sing as much as males. These differences have been known for a long time   and are generally attributed to the much less regular and seasonal climate of Australian and African arid zones requiring that birds breed at any time when conditions are favourable, although they cannot breed in many years because food supply never increases above a minimal level.  With aseasonal irregular breeding, both sexes must be brought into breeding condition and vocalisation, especially duetting, serves this purpose. The high frequency of female vocalisations in the tropics, Australia and Southern Africa may also relate to very low mortality rates producing much stronger pair-bonding and territoriality. 
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.
One of the two main functions of bird song is mate attraction.  Scientists hypothesize that bird song 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. Therefore, a female bird may select males based on the quality of their songs and the size of their song repertoire.
The second principal function of bird song is territory defense.  Territorial birds will interact with each other using song to negotiate territory boundaries. Since song may be a reliable indicator of quality, individuals may be able to discern the quality of rivals and prevent an energetically costly fight.  In birds with song repertoires, individuals may share the same song type and use these song types for more complex communication.  Some birds will respond to a shared song type with a song-type match (i.e. with the same song type).  This may be an aggressive signal; however, results are mixed.  Birds may also interact using repertoire-matches, wherein a bird responds with a song type that is in its rival's repertoire but is not the song that it is currently singing.  This may be a less aggressive act than song-type matching.  Song complexity is also linked to male territorial defense, with more complex songs being perceived as a greater territorial threat. 
Communication through bird calls can be between individuals of the same species or even across species. Birds communicate alarm through vocalizations and movements that are specific to the threat, and bird alarms can be understood by other animal species, including other birds, in order to identify and protect against the specific threat.  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 that 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,  babblers such as the scimitar babblers, and 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.
Sometimes, songs vocalized in the post-breeding season act as a cue to conspecific eavesdroppers.  In black-throated blue warblers, males that have bred and reproduced successfully sing to their offspring to influence their vocal development, while males that have failed to reproduce usually abandon the nests and stay silent. The post-breeding song therefore inadvertently informs the unsuccessful males of particular habitats that have a higher likelihood of reproductive success. The social communication by vocalization provides a shortcut to locating high quality habitats and saves the trouble of directly assessing various vegetation structures.
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, or protect against predation, but strong support is lacking for any function.  Many birds, especially those that nest in cavities, are known to produce a snakelike hissing sound that may help deter predators at close range. 
Some cave-dwelling species, including the oilbird  and swiftlets ( Collocalia and Aerodramus species),  use audible sound (with the majority of sonic location occurring between 2 and 5 kHz ) to echolocate in the darkness of caves. The only bird known to make use of infrasound (at about 20 Hz) is the western capercaillie. 
The hearing range of birds is from below 50 Hz ( infrasound) to around 12 kHz, with maximum sensitivity between 1 and 5 kHz.   The black jacobin is exceptional in producing sounds at about 11.8 kHz. It is not known if they can hear these sounds. 
The range of frequencies at which birds call in an environment varies with the quality of habitat and the ambient sounds. The acoustic adaptation hypothesis predicts that narrow bandwidths, low frequencies, 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 open habitats, without obstructive vegetation.   
Low frequency songs are optimal for obstructed, densely vegetated habitats because low frequency, slowly modulated song elements are less susceptible to signal degradation by means of reverberations off of sound-reflecting vegetation. High frequency calls with rapid modulations are optimal for open habitats because they degrade less across open space.   The acoustic adaptation hypothesis also states that song characteristics may take advantage of beneficial acoustic properties of the environment. Narrow-frequency bandwidth notes are increased in volume and length by reverberations in densely vegetated habitats. 
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.   Traffic noise was found to decrease reproductive success in the great tit (Parus major) due to the overlap in acoustic frequency.  During the COVID-19 pandemic, reduced traffic noise led to birds in San Francisco singing 30% more softly.  An increase in song volume restored fitness to birds in urban areas, as did higher frequency songs. 
It has been proposed that birds show latitudinal variation in song complexity, however there is no strong evidence that song complexity increases with latitude or migratory behaviour. 
According to a study published in 2019, the white bellbird makes the loudest call ever recorded for birds, reaching 125 dB.   The record was previously held by the screaming piha with 116 dB. 
The acquisition and learning of bird song involves a group of distinct brain areas that are aligned in two connecting pathways: 
- Anterior forebrain pathway ( vocal learning): composed of Area X, which is a homologue to mammalian basal ganglia; the lateral part of the magnocellular nucleus of anterior nidopallium (LMAN), also considered a part of the avian basal ganglia; and the dorso-lateral division of the medial thalamus (DLM).
- Posterior descending pathway (vocal production): composed of HVC (proper name, although sometimes referred to as the high vocal center); the robust nucleus of the arcopallium (RA); and the tracheosyringeal part of the hypoglossal nucleus (nXIIts).  
The posterior descending pathway (PDP) is required throughout a bird's life for normal song production, while the anterior forebrain pathway (AFP) is necessary for song learning, plasticity, and maintenance, but not for adult song production. 
Both neural pathways in the song system begin at the level of HVC, which projects information both to the RA (premotor nucleus) and to Area X of the anterior forebrain. Information in the posterior descending pathway (also referred to as the vocal production or motor pathway) descends from HVC to RA, and then from RA to the tracheosyringeal part of the hypoglossal nerve (nXIIts), which then controls muscular contractions of the syrinx.  
Information in the anterior forebrain pathway is projected from HVC to Area X (basal ganglia), then from Area X to the DLM (thalamus), and from DLM to LMAN, which then links the vocal learning and vocal production pathways through connections back to the RA. Some investigators have posited a model in which the connection between LMAN and RA carries an instructive signal based on evaluation of auditory feedback (comparing the bird's own song to the memorized song template), which adaptively alters the motor program for song output.   The generation of this instructive signal could be facilitated by auditory neurons in Area X and LMAN that show selectivity for the temporal qualities of the bird's own song (BOS) and its tutor song, providing a platform for comparing the BOS and the memorized tutor song.  
Models regarding the real-time error-correction interactions between the AFP and PDP will be considered in the future. Other current research has begun to explore the cellular mechanisms underlying HVC control of temporal patterns of song structure and RA control of syllable production.  Brain structures involved in both pathways show sexual dimorphism in many bird species, usually causing males and females to sing differently. Some of the known types of dimorphisms in the brain include the size of nuclei, the number of neurons present, and the number of neurons connecting one nucleus to another. 
In the extremely dimorphic zebra finches (Taeniopygia guttata), a species in which only males typically sing, the size of the HVC and RA are approximately three to six times larger in males than in females, and Area X does not appear to be recognizable in females.  Research suggests that exposure to sex steroids during early development is partially responsible for these differences in the brain. Female zebra finches treated with estradiol after hatching followed by testosterone or dihydrotestosterone (DHT) treatment in adulthood will develop an RA and HVC similar in size to males and will also display male-like singing behavior. 
Hormone treatment alone does not seem to produce female finches with brain structures or behavior exactly like males. Furthermore, other research has shown results that contradict what would be expected based on our current knowledge of mammalian sexual differentiation. For example, male zebra finches castrated or given sex steroid inhibitors as hatchlings still develop normal masculine singing behavior.  This suggests that other factors, such as the activation of genes on the z chromosome, might also play a role in normal male song development. 
Hormones also have activational effects on singing and the song nuclei in adult birds. In canaries (Serinus canaria), females normally sing less often and with less complexity than males. However, when adult females are given androgen injections, their singing will increase to an almost male-like frequency.  Furthermore, adult females injected with androgens also show an increased size in the HVC and RA regions.  Melatonin is another hormone that is also believed to influence song behavior in adults, as many songbirds show melatonin receptors in neurons of the song nuclei. 
Both the European starling (Sturnus vulgaris) and house sparrow (Passer domesticus) have demonstrated changes in song nuclei correlated with differing exposures to darkness and secretions of melatonin.   This suggests that melatonin might play a role in the seasonal changes of singing behavior in songbirds that live in areas where the amount of daylight varies significantly throughout the year. Several other studies have looked at seasonal changes in the morphology of brain structures within the song system and have found that these changes (adult neurogenesis, gene expression) are dictated by photoperiod, hormonal changes and behavior.  
The gene FOXP2, defects of which affect both speech production and comprehension of language in humans, becomes highly expressed in Area X during periods of vocal plasticity in both juvenile zebra finches and adult canaries. 
The songs of different species of birds vary and are generally typical of the species. 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); individuals within some species vary in the same way. In a few species, such as lyrebirds 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 learned calls, and cross-fostering experiments succeeded in making linnet Acanthis cannabina 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. 
Song learning in juvenile birds occurs in two stages: sensory learning, which involves the juvenile listening to the father or other conspecific bird and memorizing the spectral and temporal qualities of the song (song template), and sensorimotor learning, which involves the juvenile bird producing its own vocalizations and practicing its song until it accurately matches the memorized song template. 
During the sensorimotor learning phase, song production begins with highly variable sub-vocalizations called "sub-song", which is akin to babbling in human infants. Soon after, the juvenile song shows certain recognizable characteristics of the imitated adult song, but still lacks the stereotypy of the crystallized song – this is called "plastic song". 
After two or three months of song learning and rehearsal (depending on species), the juvenile produces a crystallized song, characterized by spectral and temporal stereotypy (very low variability in syllable production and syllable order).  Some birds, such as zebra finches, which are the most popular species for birdsong research, have overlapping sensory and sensorimotor learning stages. 
Research has indicated that birds' acquisition of song is a form of motor learning that involves regions of the basal ganglia. Further, the PDP (see Neuroanatomy below) has been considered homologous to a mammalian motor pathway originating in the cerebral cortex and descending through the brain stem, while the AFP has been considered homologous to the mammalian cortical pathway through the basal ganglia and thalamus.  Models of bird-song motor learning can be useful in developing 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 to identify kin and to adapt their songs to different acoustic environments. 
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, called "isolate song", resembles the song of a wild bird, it shows distinctly different characteristics from the wild song and lacks its complexity.   The importance of the bird being able to hear itself sing in the sensorimotor period was later discovered by Konishi. Birds deafened before the song-crystallization period went on to produce songs that were distinctly different from the wild type and isolate song.   Since the emergence of these findings, investigators have been searching for the neural pathways that facilitate sensory/sensorimotor learning and mediating the matching of the bird's own song with the memorized song template.
Several studies over recent decades have looked at the neural mechanisms underlying birdsong learning by performing lesions to relevant brain structures involved in the production or maintenance of song or by deafening birds before and/or after song crystallization. Another recent experimental approach was recording the bird's song and then playing it back while the bird is singing, causing perturbed auditory feedback (the bird hears the superposition of its own song and a fragmented portion of a previous song syllable).  After Nordeen & Nordeen  made a landmark discovery as they demonstrated that auditory feedback was necessary for the maintenance of song in adult birds with crystallized song, Leonardo & Konishi (1999) designed an auditory feedback perturbation protocol in order to explore the role of auditory feedback in adult song maintenance further, to investigate how adult songs deteriorate after extended exposure to perturbed auditory feedback, and to examine the degree to which adult birds could recover crystallized song over time after being removed from perturbed feedback exposure. This study offered further support for role of auditory feedback in maintaining adult song stability and demonstrated how adult maintenance of crystallized birdsong is dynamic rather than static.
Brainard & Doupe (2000) posit a model in which LMAN (of the anterior forebrain) plays a primary role in error correction, as it detects differences between the song produced by the bird and its memorized song template and then sends an instructive error signal to structures in the vocal production pathway in order to correct or modify the motor program for song production. In their study, Brainard & Doupe (2000) showed that while deafening adult birds led to the loss of song stereotypy due to altered auditory feedback and non-adaptive modification of the motor program, lesioning LMAN in the anterior forebrain pathway of adult birds that had been deafened led to the stabilization of song (LMAN lesions in deafened birds prevented any further deterioration in syllable production and song structure).
Currently, there are two competing models that elucidate the role of LMAN in generating an instructive error signal and projecting it to the motor production pathway:
Bird's own song (BOS)-tuned error correction model
- During singing, the activation of LMAN neurons will depend on the match between auditory feedback from the song produced by the bird and the stored song template. If this is true, then the firing rates of LMAN neurons will be sensitive to changes in auditory feedback.
Efference copy model of error correction
- An efference copy of the motor command for song production is the basis of the real-time error-correction signal. During singing, activation of LMAN neurons will depend on the motor signal used to generate the song, and the learned prediction of expected auditory feedback based on that motor command. Error correction would occur more rapidly in this model.
Leonardo  tested these models directly by recording spike rates in single LMAN neurons of adult zebra finches during singing in conditions with normal and perturbed auditory feedback. His results did not support the BOS-tuned error correction model, as the firing rates of LMAN neurons were unaffected by changes in auditory feedback and therefore, the error signal generated by LMAN appeared unrelated to auditory feedback. Moreover, the results from this study supported the predictions of the efference copy model, in which LMAN neurons are activated during singing by the efference copy of the motor signal (and its predictions of expected auditory feedback), allowing the neurons to be more precisely time-locked to changes in auditory feedback.
A mirror neuron is a neuron that discharges both when an individual performs an action and when he/she perceives that same action being performed by another.  These neurons were first discovered in macaque monkeys, but recent research suggests that mirror neuron systems may be present in other animals including humans. 
Mirror neurons have the following characteristics: 
- They are located in 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.  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, how it compares to a memorized song template, and what he produces.
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.  They discovered that the neurons that project from the HVC to Area X (HVCX 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 HVCX 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.
Prather, et al. found that during the short period of time before and after the bird sings, his HVCX 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.  This may be the mechanism underlying learning via auditory feedback. These findings are also in line with Leonardo's (2004) efference copy model of error correction in birdsong learning and production.
Overall, the HVCX auditory motor neurons in swamp sparrows are very similar to the visual motor mirror neurons discovered in primates. Like mirror neurons, the HVCX 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.  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.  
Culture in animals is usually defined to consist of socially transmitted behavior patterns ("traditions") that are characteristic of certain populations.  The learned nature of bird song as well as evidence of "dialect"-like local variations have led some researchers to hypothesize the existence of avian culture.
As mentioned above, bird song's dependence on learning was studied by Thorpe, who found that chaffinches raised in isolation from their first week of life produce highly abnormal and less complex songs compared to other chaffinches.  This suggested that many aspects of song development in songbirds depends on tutoring by older members of the same species. Later studies observed canary-like elements in the song of a chaffinch raised by canaries,  evidencing the strong role of tutors in the learning of song by juvenile birds.
Similar chaffinch song types (categorized based on their distinct elements and their order) were observed to cluster in similar geographic areas,  and this discovery led to hypotheses about "dialects" in birdsong. It has since been postulated that these song type variations are not dialects like those we found in human language. This is because not all members of a given geographic area will conform to the same song type, and also because there is no singular characteristic of a song type that differentiates it from all other types (unlike human dialects where certain words are unique to certain dialects). 
Based on this evidence of learning and localized song types, researchers began to investigate the social learning of birdsong as a form of cultural transmission. The behavior patterns constituting this culture are the songs themselves, and the song types can be considered as traditions.
A recent study has shown that a dopamine circuit in zebra finches may promote social learning of bird song from tutors.  Their data shows that certain brain areas in juvenile zebra finches are excited by the singing of conspecific (i.e. same-species) tutors and not by loudspeakers playing zebra finch song. Additionally, they show that dopamine released into the HVC aids in the encoding of song.
Although a significant amount of research was done on bird song during the 20th century, none was able to elucidate the evolutionary "use" behind birdsong, especially with regards to large vocal repertoires. In response, Lachlan and Slater proposed a "cultural trap" model to explain persistence of wide varieties of song.  This model is in based on a concept of "filters", in which:
- a male songbird's (i.e. singer's) filter contains the range of songs that it can develop
- a female songbird's (i.e. receiver's) filter contains the range of songs that it finds acceptable for mate choice
In one possible situation, the population consists mainly of birds with wide filters. In this population, a male songbird with a wide filter will rarely be chosen by the few female with narrow filters (as the male's song is unlikely to fall within a narrower filter). This female will now have a relatively small choice of males to mate with, and so the genetic basis of the female's narrow filter would not persist. Another possible situation deals with a population with mostly narrow-filters. In the latter population, wide-filter males can feasibly avoid mate choice rejection by learning from older, narrow-filter males. Therefore, the average reproductive success of wide-filter birds is enhanced by the possibility of learning, and vocal learning and large song repertoires (i.e. wide filters) go hand-in-hand.  
The cultural trap hypothesis is one example of gene-culture coevolution, in which selective pressures emerge from the interaction between genotypes and their cultural consequences. 
Various studies have shown that adult birds that underwent stress during critical developmental periods produce less complex songs and have smaller HVC brain regions.   These has led some researchers to hypothesize that sexual selection for more complex songs indirectly selects for stronger cognitive ability in males.  Further investigation showed that male song sparrows with larger vocal repertoires required less time to solve detour-reaching cognitive tasks.  Some have proposed that bird song (among other sexually selected traits such as flashy coloring, body symmetry, and elaborate courtship) allow female songbirds to quickly assess the cognitive skills and development of multiple males.
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 term "warblish" has been coined to explain this approach to bird call description. 
Kay Electric Company started by former Bell Labs engineers Harry Foster and Elmo Crump made a device that was marketed as the "Sona-Graph" in 1948. This was adopted by early researchers  including C.E.G.Bailey who demonstrated its use for studying bird song in 1950.  The use of spectrograms to visualize bird song was then adopted by Donald J. Borror  and developed further by others including W. H. Thorpe.   These visual representations are also called sonograms or sonagrams. Beginning in 1983, some 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. 
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 chickens 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, grammar (that is, structures and rules). Studies to demonstrate the existence of language have been difficult due to the range of possible interpretations. For instance, some have argued that in order for a communication system to count as a language it must be "combinatorial",  having an open ended set of grammar-compliant sentences made from a finite vocabulary.
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.  In the wild, Black-capped Chickadees innate vocalizations have been rigorously shown  to have combinatorial language. Studies on starling vocalizations have also suggested that they may have recursive structures. 
The term bird language may also more informally refer to patterns in bird vocalizations that communicate information to other birds or other animals in general. 
Some birds have two distinct "languages", one for internal communications and one for use in flocks. All birds have a separate type of communication for "songs" vs. communicating danger and other information. Konrad Lorenz demonstrated that Jackdaws have "names" identifying each individual in the flock and when beginning flight preparations each of them say one other bird's name creating a "chain". In his book King Solomon's Ring, he describes the name he was given by the birds and how he was recognized several years later in a far away location following WWII.
Studies in parakeets have shown a striking similarity between talking bird's verbal areas in the brain and the equivalent human brain areas, suggesting that mimicry has much to do with the construction of language and its structures and order.  Recent research showed birds construct sentence like communications with a syntax and grammar. 
This section needs expansion. You can help by adding to it. (September 2011)
In music, birdsong has influenced composers and musicians in several ways: they can be inspired by birdsong; they can intentionally imitate bird song in a composition, as Vivaldi and Beethoven did, along with many later composers; they can incorporate recordings of birds into their works, as Ottorino Respighi first did; or like Beatrice Harrison and David Rothenberg, they can duet with birds.     Authors including Rothenberg have claimed that birds sing on traditional scales as used in human music,    but at least one songbird does not choose notes in this way. 
Among birds which habitually borrow phrases or sounds from other species, the way they use variations of rhythm, relationships of musical pitch, and combinations of notes can resemble music.  Hollis Taylor's in-depth analysis of pied butcherbird vocalizations provides a detailed rebuttal to objections of birdsong being judged as music.  The similar motor constraints on human and avian song may have driven these to have similar song structures, including "arch-shaped and descending melodic contours in musical phrases", long notes at the ends of phrases, and typically small differences in pitch between adjacent notes, at least in birds with a strong song structure like the Eurasian treecreeper Certhia familiaris. 
Bird song is a popular subject in poetry. Famous examples inspired by bird song include the 1177 Persian poem " The Conference of the Birds", in which the birds of the world assemble under the wisest bird, the hoopoe, to decide who is to be their king.  In English poetry, John Keats's 1819 " Ode to a Nightingale" and Percy Bysshe Shelley's 1820 " To a Skylark" are popular classics.   Ted Hughes's 1970 collection of poems about a bird character, " Crow", is considered one of his most important works.  Bird poems by Gerard Manley Hopkins include "Sea and Skylark" and " The Windhover". 
- Sclater, P. L. (1860). "List of Birds collected by Mr. Fraser in Ecuador, at Nanegal, Calacali, Perucho, and Puellaro, with notes and descriptions of new species". Proc. Zool. Soc. London: 83–97.
- Darwin, Charles (1871). The descent of man and selection in relation to sex. volume 2. London: John Murray. pp. 65–66. ISBN 978-1-108-00510-4.
- Boswall, Jeffery. "Why do birds sing?". The British Library. Archived from the original on 29 January 2020.
- Ehrlich, Paul R.; David S. Dobkin & Darryl Wheye. ""Bird Voices" and "Vocal Development" from Birds of Stanford essays". Retrieved 9 Sep 2008.
- Howell, Steve N. G. & Sophie Webb (1995). A Guide to the Birds of Mexico and Northern Central America. Oxford University Press. ISBN 978-0-19-854012-0.
- Bostwick, Kimberly S. & Richard O. Prum (2005). "Courting Bird Sings with Stridulating Wing Feathers". Science. 309 (5735): 736. doi: 10.1126/science.1111701. PMID 16051789. S2CID 22278735.
- 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.
- Bostwick, Kimberly S. & Richard O. Prum (2003). "High-speed video analysis of wing-snapping in two manakin clades (Pipridae: Aves)". The Journal of Experimental Biology. 206 (Pt 20): 3693–3706. doi: 10.1242/jeb.00598. PMID 12966061. S2CID 8614009.
- Robinson, Angus; "The Biological Significance of Bird Song in Australia" in Emu; 48(4), pp. 291-315
- Hartshorne, Charles; "Some Biological Principles Applicable to Song Behavior" in The Wilson Bulletin Vol. 70, No. 1 (Mar., 1958), pp. 41-56
- Slater Peter J. B., Mann Nigel I. (2004). "Why do the females of many bird species sing in the tropics?". Journal of Avian Biology. 35 (4): 289–294. doi: 10.1111/j.0908-8857.2004.03392.x.
- Attenborough, D. 1998. The Life of Birds. BBC publication.0563-38792-0
- Australian Museum Online. "Crows and Ravens". Archived from the original on 1 September 2007. Retrieved 12 August 2007.
- Catchpole, C.; Slater, P.J.B (2008). Bird Song: Biological Themes and Variation. Cambridge University Press.
- Mikula, P.; Valcu, M.; Brumm, H.; Bulla, M.; Forstmeier, W.; Petrusková, T.; Kempenaers, B. & Albrecht, T. (2021). "A global analysis of song frequency in passerines provides no support for the acoustic adaptation hypothesis but suggests a role for sexual selection". Ecology Letters. 24 (3): 477–486. doi: 10.1111/ele.13662. PMID 33314573.
- Garamszegi, L. Z.; A. P. Møller; János Török; Gábor Michl; Péter Péczely; Murielle Richard (2004). "Immune challenge mediates vocal communication in a passerine bird: an experiment" (PDF). Behavioral Ecology. 15 (1): 148–157. doi: 10.1093/beheco/arg108.
- Redpath, S. M.; Bridget M Appleby; Steve J Petty (2000). "Do male hoots betray parasite loads in Tawny Owls?". Journal of Avian Biology. 31 (4): 457–462. doi: 10.1034/j.1600-048X.2000.310404.x.
- Reid, J. M.; Peter Arcese; Alice L. E. V. Cassidy; Sara M. Hiebert; James N. M. Smith; Philip K. Stoddard; Amy B. Marr & Lukas F. Keller (2005). "Fitness Correlates of Song Repertoire Size in Free-Living Song Sparrows (Melospiza melodia)" (PDF). The American Naturalist. 165 (3): 299–310. doi: 10.1086/428299. PMID 15729661. S2CID 12547933.
- Møller AP; J. Erritzøe; L. Z. Garamszegi (2005). "Covariation between brain size and immunity in birds: implications for brain size evolution" (PDF). Journal of Evolutionary Biology. 18 (1): 223–237. CiteSeerX 10.1.1.585.3938. doi: 10.1111/j.1420-9101.2004.00805.x. PMID 15669979. S2CID 21763448.
- Searcy, W. A.; Beecher, M.D. (2009). "Song as an aggressive signal in songbirds". Animal Behaviour. 78 (6): 1281–1292. doi: 10.1016/j.anbehav.2009.08.011. S2CID 30360474.
- Falls, J. B.; Krebs, J. R.; McGregor, P.K. (1982). "Song matching in the great tit (Parus major) the effect of similarity and familiarity". Animal Behaviour. 30 (4): 997–1009. doi: 10.1016/S0003-3472(82)80188-7. S2CID 53189625.
- Beecher, M.D.; Stoddard, P.K.; Cambell, E.S.; Horning, C.L. (1996). "Repertoire matching between neighbouring song sparrows". Animal Behaviour. 51 (4): 917–923. doi: 10.1006/anbe.1996.0095. S2CID 26372750.
- Hill, S. D.; Brunton, D. H.; Anderson, M. A.; Weihong, J. (2018). "Fighting talk: complex song elicits more aggressive responses in a vocally complex songbird". Ibis. 160 (2): 257–268. doi: 10.1111/ibi.12542.
- "A Bird's World: Speaking in a Bird's Language". Museum of Science, Boston. 2008.
- Marler, P. (1955). "Characteristics of some animal calls". Nature. 176 (4470): 6–8. Bibcode: 1955Natur.176....6M. doi: 10.1038/176006a0. S2CID 4199385.
- Lengagne, T.; J. Lauga & T. Aubin (2001). "Intra-syllabic acoustic signatures used by the King Penguin in parent-chick recognition: an experimental approach" (PDF). The Journal of Experimental Biology. 204 (Pt 4): 663–672. doi: 10.1242/jeb.204.4.663. PMID 11171348.
- Wayne Delport; Alan C Kemp; J. Willem H Ferguson (2002). "Vocal identification of individual African Wood Owls Strix woodfordii: a technique to monitor long-term adult turnover and residency". Ibis. 144 (1): 30–39. doi: 10.1046/j.0019-1019.2001.00019.x.
- Thorpe, W. H. (23 February 1963). "Antiphonal Singing in Birds as Evidence for Avian Auditory Reaction Time". Nature. 197 (4869): 774–776. Bibcode: 1963Natur.197..774T. doi: 10.1038/197774a0. S2CID 30542781.
- Stokes, A. W.; H. W. Williams (1968). "Antiphonal calling in quail" (PDF). Auk. 85 (1): 83–89. doi: 10.2307/4083626. JSTOR 4083626.
- Harris, Tony; Franklin, Kim (2000). Shrikes and Bush-Shrikes. Princeton University Press. pp. 257–260. ISBN 978-0-691-07036-0.
- Osmaston, B. B. (1941). ""Duetting" in birds". Ibis. 5 (2): 310–311. doi: 10.1111/j.1474-919X.1941.tb00620.x.
- Power, D. M. (1966). "Antiphonal duetting and evidence for auditory reaction time in the Orange-chinned Parakeet". Auk. 83 (2): 314–319. doi: 10.2307/4083033. JSTOR 4083033.
- Hyman, Jeremy (2003). "Countersinging as a signal of aggression in a territorial songbird" (PDF). Animal Behaviour. 65 (6): 1179–1185. doi: 10.1006/anbe.2003.2175. S2CID 38239656.
- Betts, M.G.; Hadley, A.S.; Rodenhouse, N.; Nocera, J.J. (2008). "Social Information Trumps Vegetation Structure in Breeding-Site Selection by a Migrant Songbird". Proceedings: Biological Sciences. 1648. 275 (1648): 2257–2263. doi: 10.1098/rspb.2008.0217. PMC 2603235. PMID 18559326.
- Goodale, E. & Kotagama, S. W. (2005). "Testing the roles of species in mixed-species bird flocks of a Sri Lankan rain forest". Journal of Tropical Ecology. 21 (6): 669–676. doi: 10.1017/S0266467405002609. S2CID 86000560.
- Kelley, L. A.; Coe, R. L.; Madden, J. R.; Healy, S. D. (2008). "Vocal mimicry in songbirds". Animal Behaviour. 76 (3): 521–528. doi: 10.1016/j.anbehav.2008.04.012. S2CID 53192695.
- Marler, Peter; Hans Willem Slabbekoorn (2004). Nature's music: the science of birdsong. Academic Press. p. 145. ISBN 978-0-12-473070-0.
- Suthers RA & Hector DH (1985). "The physiology of vocalization by the echolocating Oilbird, Steatornis caripensis". J. Comp. Physiol. 156 (2): 243–266. doi: 10.1007/BF00610867. S2CID 1279919.
- Suthers RA & Hector DH (1982). "Mechanism for the production of echolocating clicks by the Grey Swiftlet, Collocalia spodiopygia". J. Comp. Physiol. A. 148 (4): 457–470. doi: 10.1007/BF00619784. S2CID 39111110.
- Coles RB; Konishi M & Pettigrew JD (1987). "Hearing and echolocation in the Australian Grey Swiftlet, Collocalia spodiopygia". J. Exp. Biol. 129: 365–371. doi: 10.1242/jeb.129.1.365.
- Lieser M; P. Berthold1 & G. A. Manley (2005). "Infrasound in the capercaillie ( Tetrao urogallus )". Journal of Ornithology. 146 (4): 395–398. doi: 10.1007/s10336-005-0003-y. S2CID 22412727.
- Dooling, R.J. (1982). Auditory perception in birds. Acoustic Communication in Birds, Vol. 1 (eds D.E. Kroodsma & E.H. Miller). pp. 95–130.
- Olson, Christopher R.; Fernández-Vargas, Marcela; Portfors, Christine V.; Mello, Claudio V. (2018). "Black Jacobin hummingbirds vocalize above the known hearing range of birds". Current Biology. 28 (5): R204–R205. doi: 10.1016/j.cub.2018.01.041. PMID 29510104. S2CID 3727714.
- Derryberry, Elizabeth (July 2009). "Ecology Shapes Birdsong Evolution: Variation in Morphology and Habitat Explains Variation in White-Crowned Sparrow Song". The American Naturalist. 174 (1): 24–33. doi: 10.1086/599298. PMID 19441960. S2CID 8606774.
- Boncoraglio, G. & Nicola Saino (2007). "Habitat structure and the evolution of bird song: a meta-analysis of the evidence for the acoustic adaptation hypothesis". Functional Ecology. 21: 134–142. doi: 10.1111/j.1365-2435.2006.01207.x.
- Morton, E.S. (1975). "Ecological sources of selection on avian sounds". American Naturalist. 109 (965): 17–34. doi: 10.1086/282971. S2CID 55261842.
- Ey, Elodie; Fischer, J. (13 April 2012). "The "acoustic adaptation hypothesis" - a review of the evidence from birds, anurans and mammals". Bioacoustics. 19 (1–2): 21–48. doi: 10.1080/09524622.2009.9753613. S2CID 84971439.
- Tubaro, Pablo L.; Segura, Enrique T. (November 1994). "Dialect Differences in the Song of Zonotrichia capensis in the Southern Pampas: A Test of the Acoustic Adaptation Hypothesis". The Condor. 96 (4): 1084–1088. doi: 10.2307/1369117. JSTOR 1369117.
- Slabbekoorn, Hans; Ellers, Jacintha; Smith, Thomas B. (2002). "Birdsong and sound transmission: the benefits of reverberations" (PDF). The Condor. 104 (3): 564–573. doi: 10.1650/0010-5422(2002)104[0564:basttb]2.0.co;2.
- Krause, Bernard L. (1993). "The Niche Hypothesis" (PDF). The Soundscape Newsletter. 06. Archived from the original (PDF) on 2008-03-07.
- Henrik Brumm (2004). "The impact of environmental noise on song amplitude in a territorial bird". Journal of Animal Ecology. 73 (3): 434–440. doi: 10.1111/j.0021-8790.2004.00814.x. S2CID 73714706.
- Slabbekoorn, H. & Peet, M. (2003). "Birds sing at a higher pitch in urban noise". Nature. 424 (6946): 267. Bibcode: 2003Natur.424..267S. doi: 10.1038/424267a. PMID 12867967. S2CID 4348883.
- Halfwerk, Wouter; Holleman, L.J.M.; Lessells, C.M.; Slabbekoorn, H. (February 2011). "Negative impact of traffic nosie on avian reproductive success". Journal of Applied Ecology. 48 (1): 210–219. doi: 10.1111/j.1365-2664.2010.01914.x. S2CID 83619284.
- Stokstad, Erik (24 September 2020). "When COVID-19 silenced cities, birdsong recaptured its former glory". Science. Retrieved 28 May 2021.
- Luther, David A.; Derryberry, E.P. (April 2012). "Birdsongs keep pace with city life: changes in song over time in an urban songbird affects communication". Animal Behaviour. 83 (4): 1059–1066. doi: 10.1016/j.anbehav.2012.01.034. S2CID 31212627.
- Najar, N.; Benedict, L. (2019). "The relationship between latitude, migration and the evolution of bird song complexity". Ibis. 161 (1): 1–12. doi: 10.1111/ibi.12648.
- Jeffrey Podos; Mario Cohn-Haft (21 October 2019). "Extremely loud mating songs at close range in white bellbirds". Current Biology. 29 (20): R1068–R1069. doi: 10.1016/j.cub.2019.09.028. PMID 31639347. S2CID 204823663.
- "World's 'loudest bird': Meet the white bellbird". Newsbeat (video). BBC News. 22 October 2019.
- NEMETH, ERWIN (2004-01-01). "Measuring the Sound Pressure Level of the Song of the Screaming Piha Lipaugus Vociferans: One of the Loudest Birds in the World?". Bioacoustics. 14 (3): 225–228. doi: 10.1080/09524622.2004.9753527. ISSN 0952-4622. S2CID 84218370.
- Nottebohm, F. (2005). "The Neural Basis of Birdsong". PLOS Biol. 3 (5): 163. doi: 10.1371/journal.pbio.0030164. PMC 1110917. PMID 15884976.
- Brainard, M. S. & Doupe, A. J. (2000). "Auditory feedback in learning and maintenance of vocal behavior". Nature Reviews Neuroscience. 1 (1): 31–40. doi: 10.1038/35036205. PMID 11252766. S2CID 5133196.
- Carew, Thomas J. (2000). Behavioral Neurobiology: The Cellular Organization of Natural Behavior. Sinauer Associates. ISBN 978-0-87893-092-0.
- Kao, M.H.; Doupe, A.J.; Brainard, M.S. (2005). "Contributions of an avian basal ganglia-forebrain circuit to real=time modulation of song". Nature. 433 (7026): 638–642. Bibcode: 2005Natur.433..638K. doi: 10.1038/nature03127. PMID 15703748. S2CID 4352436.
- Suthers, R. (2004). "How birds sing and why it matters". In Marler, P.; Slabbekoorn, H. (eds.). Nature's music:The science of birdsong. Academic Press. pp. 272–295. ISBN 978-0-12-473070-0.
- Brainard, M. S. & Doupe, A. J. (2000). "Interruption of a basal ganglia-forebrain circuit prevents plasticity of learned vocalizations". Nature. 404 (6779): 762–766. Bibcode: 2000Natur.404..762B. doi: 10.1038/35008083. PMID 10783889. S2CID 4413588.
- Kojima, S.; Doupe, A. (2008). "Neural encoding of auditory temporal context in a songbird basal ganglia nucleus, and its independence of birds' song experience". European Journal of Neuroscience. 27 (5): 1231–1244. doi: 10.1111/j.1460-9568.2008.06083.x. PMC 2408885. PMID 18364039.
- Long, M.A.; Jin, D.Z.; Fee, M.S. (2010). "Support for a synaptic chain model of neuronal sequence generation". Nature. 468 (7322): 394–399. Bibcode: 2010Natur.468..394L. doi: 10.1038/nature09514. PMC 2998755. PMID 20972420.
- Balthazart, J.; Adkins-Regan (2002). Sexual differentiation of brain and behavior in birds. Hormones, Brain and Behavior. 4. pp. 223–301. doi: 10.1016/b978-012532104-4/50068-8. ISBN 9780125321044. PMID 18406680.
- Nottebohm, F. & Arnold, A.P. (1976). "Sexual dimorphism in vocal control areas of the songbird brain". Science. 194 (4261): 211–213. Bibcode: 1976Sci...194..211N. doi: 10.1126/science.959852. PMID 959852.
- Gurney, M.E. & Konishi, M. (1980). "Hormone-induced sexual differentiation of brain and behavior in zebra finches". Science. 208 (4450): 1380–1383. Bibcode: 1980Sci...208.1380G. doi: 10.1126/science.208.4450.1380. PMID 17775725. S2CID 11669349.
- Tomaszycki, M.L.; Peabody, C.; Replogle, K.; Clayton, D.F; Tempelman, R.J.; Wade, J. (2009). "Sexual differentiation of the zebra finch song system: potential roles for sex chromosome genes". BMC Neuroscience. 10: 24. doi: 10.1186/1471-2202-10-24. PMC 2664819. PMID 19309515.
- Leonard, S. L. (1 May 1939). "Induction of Singing in Female Canaries by Injections of Male Hormone". Experimental Biology and Medicine. 41 (1): 229–230. doi: 10.3181/00379727-41-10631. S2CID 87078020.
- Nottebohm, F. (1980). "Testosterone triggers growth of brain vocal control nuclei in adult female canaries". Brain Research. 189 (2): 429–36. doi: 10.1016/0006-8993(80)90102-X. PMID 7370785. S2CID 25845332.
- Ball, G.F. & Balthazart, J. (2002). Neuroendocrine mechanisms regulating reproductive cycles and reproductive behavior in birds. Hormones, Brain, and Behavior. 2. pp. 649–798. doi: 10.1016/b978-012532104-4/50034-2. ISBN 9780125321044.
- Bentley, G.E.; Van't Hof, T.J.; Ball, G.F. (1999). "Seasonal neuroplasticity in the songbird telencephalon: A role for melatonin". Proceedings of the National Academy of Sciences of the United States of America. 96 (8): 4674–4679. Bibcode: 1999PNAS...96.4674B. doi: 10.1073/pnas.96.8.4674. PMC 16391. PMID 10200321.
- Cassone, V.M.; Bartell, P.A.; Earnest D.J. & Kumar, V. (2008). "Duration of melatonin regulates seasonal changes in song control nuclei of the house sparrow, Passer domesticus: Independence from gonads and circadian entrainment". Journal of Biological Rhythms. 23 (1): 49–58. doi: 10.1177/0748730407311110. PMID 18258757. S2CID 206544790.
- Ball, G.F.; Auger, C.J.; Bernard, D.J.; Charlier, T.D.; Sartor, J.J.; Riters, L.V.; Balthazart, J. (2004). "Seasonal plasticity in the song control system: Multiple brain sites of steroid hormone action and the importance of variation in song behavior". Annals of the New York Academy of Sciences. 1016 (1): 586–610. Bibcode: 2004NYASA1016..586B. doi: 10.1196/annals.1298.043. PMID 15313796. S2CID 42818488.
- London, S.E.; Replogle, K.; Clayton, D.F. (2009). "Developmental shifts in gene expression in the auditory forebrain during the sensitive period for song learning". Developmental Neurobiology. 69 (7): 436–450. doi: 10.1002/dneu.20719. PMC 2765821. PMID 19360720.
- Scharff C; Haesler S (2005). "An evolutionary perspective on FoxP2: strictly for the birds?". Current Opinion in Neurobiology. 15 (6): 694–703. doi: 10.1016/j.conb.2005.10.004. PMID 16266802. S2CID 11350165.
- Brainard, M. S. & Doupe, A. J. (2002). "What songbirds teach us about learning". Nature. 417 (6886): 351–358. Bibcode: 2002Natur.417..351B. doi: 10.1038/417351a. PMID 12015616. S2CID 4329603.
- Barrington, D. (1773). "Experiments and observations on the singing of birds". Philosophical Transactions of the Royal Society. 63: 249–291. doi: 10.1098/rstl.1773.0031. S2CID 186207885.
- Marler, P.; M. Tamura (1962). "Song dialects in three populations of the white-crowned sparrow". Condor. 64 (5): 368–377. doi: 10.2307/1365545. JSTOR 1365545.
- Konishi, M. (2010). "From central pattern generator to sensory template in the evolution of birdsong". Brain & Language. 115 (1): 18–20. doi: 10.1016/j.bandl.2010.05.001. PMID 20955898. S2CID 205791930.
- Leonardo, A.; Konishi, M. (1999). "Decrystallization of adult birdsong by perturbation of auditory feedback". Nature. 399 (6735): 466–470. Bibcode: 1999Natur.399..466L. doi: 10.1038/20933. PMID 10365958. S2CID 4403659.
- Teramitsu I; Kudo LC; London SE; Geschwind DH & White SA (2004). "Parallel FoxP1 and FoxP2 expression in songbird and human brain predicts functional interaction". J. Neurosci. 24 (13): 3152–63. doi: 10.1523/JNEUROSCI.5589-03.2004. PMC 6730014. PMID 15056695.
- Nottebohm, F. (2004). "The road we travelled: discovery, choreography, and significance of brain replaceable neurons". Annals of the New York Academy of Sciences. 1016 (1): 628–658. Bibcode: 2004NYASA1016..628N. doi: 10.1196/annals.1298.027. PMID 15313798. S2CID 11828091.
- Brenowitz, Eliot A. & Michael D. Beecher (2005). "Song learning in birds: diversity and plasticity, opportunities and challenges" (PDF). Trends in Neurosciences. 28 (3): 127–132. doi: 10.1016/j.tins.2005.01.004. PMID 15749165. S2CID 14586913.
- Slater, P. J. B. (1989). "Bird song learning: causes and consequences". Ethol. Ecol. Evol. 1: 19–46. doi: 10.1080/08927014.1989.9525529.
- Thorpe, W. (1954). "The process of song-learning in the chaffinch as studied by means of the sound spectrograph". Nature. 173 (4402): 465–469. Bibcode: 1954Natur.173..465T. doi: 10.1038/173465a0. S2CID 4177465.
- Metzmacher, M. (2016). "Alauda: Chaffinch song learning : Thorpe conclusions revisited". Alauda. 84: 465–469. hdl: 2268/204189.
- Konishi, M. (1965). "The role of auditory feedback on the control of vocalization in the white-crowned sparrow". Zeitschrift für Tierpsychologie. 22 (7): 770–783. doi: 10.1111/j.1439-0310.1965.tb01688.x. PMID 5874921.
- Marler, P. (1970). "A comparative approach to vocal learning: Song development in the white-crowned sparrows". Journal of Comparative and Physiological Psychology. 71 (2, Pt.2): 1–25. doi: 10.1037/h0029144.
- Nordeen, K.W.; Nordeen, E.J. (1994). "Auditory feedback is necessary for the maintenance of stereotyped song in adult zebra finches". Behavioral and Neural Biology. 71 (1): 58–66. doi: 10.1016/0163-1047(92)90757-U. PMID 1567334.
- Leonardo, A. (2004). "Experimental test of error-correction birdsong model". Proceedings of the National Academy of Sciences of the United States of America. 101 (48): 16935–16940. doi: 10.1073/pnas.0407870101. PMC 534752. PMID 15557558.
- Rizzolatti G.; Craighero L. (2004). "The mirror-neuron system". Annu. Rev. Neurosci. 27: 169–192. doi: 10.1146/annurev.neuro.27.070203.144230. PMID 15217330. S2CID 1729870.
- Oberman L. M.; Pineda J. A.; Ramachandran V. S. (2007). "The human mirror neuron system: A link between action observation and social skills". Social Cognitive and Affective Neuroscience. 2 (1): 62–66. doi: 10.1093/scan/nsl022. PMC 2555434. PMID 18985120.
- Prather J. F.; Peters S.; Nowicki S.; Mooney R. (2008). "Precise auditory-vocal mirroring in neurons for learned vocal communication". Nature. 451 (7176): 305–310. Bibcode: 2008Natur.451..305P. doi: 10.1038/nature06492. PMID 18202651. S2CID 4344150.
- Dinstein I.; Thomas C.; Behrmann M.; Heeger D.J. (2008). "A mirror up to nature". Current Biology. 18 (1): R13–18. doi: 10.1016/j.cub.2007.11.004. PMC 2517574. PMID 18177704.
- Tchernichovski O.; Wallman J. (2008). "Behavioral neuroscience: Neurons of imitation". Nature. 451 (7176): 249–250. Bibcode: 2008Natur.451..249T. doi: 10.1038/451249a. PMID 18202627. S2CID 205035217.
- Miller G (2008). "Mirror neurons may help songbirds stay in tune". Science. 319 (5861): 269. doi: 10.1126/science.319.5861.269a. PMID 18202262. S2CID 34367648.
- Richard Mooney (5 June 2014). "Auditory–vocal mirroring in songbirds". Philosophical Transactions of the Royal Society B: Biological Sciences. Philosophical Transactions of the Royal Society B: Biological Sciences Online. 369 (1644). doi: 10.1098/rstb.2013.0179. PMC 4006181. PMID 24778375.
- Riebel, Katharina; Lachlan, Robert F.; Slater, Peter J. B. (2015-05-01), Naguib, Marc; Brockmann, H. Jane; Mitani, John C.; Simmons, Leigh W. (eds.), "Chapter Six - Learning and Cultural Transmission in Chaffinch Song", Advances in the Study of Behavior, Academic Press, 47: 181–227, doi: 10.1016/bs.asb.2015.01.001, retrieved 2020-01-30
- Thorpe, W. H. (2008-06-28). "The Learning of Song Patterns by Birds, with Especial Reference to the Song of the Chaffinch Fringilla Coelebs". Ibis. 100 (4): 535–570. doi: 10.1111/j.1474-919x.1958.tb07960.x. ISSN 0019-1019.
- Slater, P. J. B. (1983-04-01). "Chaffinch Imitates Canary Song Elements and Aspects of Organization". The Auk. 100 (2): 493–495. doi: 10.1093/auk/100.2.493. ISSN 0004-8038.
- Slater, P. J. B.; Ince, S. A. (1979). "Cultural Evolution in Chaffinch Song". Behaviour. 71 (1/2): 146–166. doi: 10.1163/156853979X00142. ISSN 0005-7959. JSTOR 4534000.
- Tanaka, Masashi; Sun, Fangmiao; Li, Yulong; Mooney, Richard (2018). "A mesocortical dopamine circuit enables the cultural transmission of vocal behaviour". Nature. 563 (7729): 117–120. Bibcode: 2018Natur.563..117T. doi: 10.1038/s41586-018-0636-7. ISSN 1476-4687. PMC 6219627. PMID 30333629.
- Lachlan, Robert F.; Slater, Peter J. B. (1999-04-07). "The maintenance of vocal learning by gene–culture interaction: the cultural trap hypothesis". Proceedings of the Royal Society B: Biological Sciences. 266 (1420): 701–706. doi: 10.1098/rspb.1999.0692. ISSN 0962-8452. PMC 1689831.
- Schmidt, K. L.; MacDougall-Shackleton, E. A.; Kubli, S. P.; MacDougall-Shackleton, S. A. (2014-06-20). "Developmental Stress, Condition, and Birdsong: A Case Study in Song Sparrows". Integrative and Comparative Biology. 54 (4): 568–577. doi: 10.1093/icb/icu090. ISSN 1540-7063. PMID 24951504.
- S., Nowicki; W., Searcy; S., Peters (2002-12-01). "Brain development, song learning and mate choice in birds: a review and experimental test of the "nutritional stress hypothesis"". Journal of Comparative Physiology A. 188 (11–12): 1003–1014. doi: 10.1007/s00359-002-0361-3. ISSN 0340-7594. PMID 12471497. S2CID 14298372.
- Boogert, N. J.; Fawcett, T. W.; Lefebvre, L. (2011-04-18). "Mate choice for cognitive traits: a review of the evidence in nonhuman vertebrates". Behavioral Ecology. 22 (3): 447–459. doi: 10.1093/beheco/arq173. ISSN 1045-2249.
- Boogert, Neeltje J.; Anderson, Rindy C.; Peters, Susan; Searcy, William A.; Nowicki, Stephen (2011). "Song repertoire size in male song sparrows correlates with detour reaching, but not with other cognitive measures". Animal Behaviour. 81 (6): 1209–1216. doi: 10.1016/j.anbehav.2011.03.004. ISSN 0003-3472. S2CID 21724914.
- Saunders, Aretas A (1951) Guide to Bird Songs. Doubleday and Company
- Sibley, David (2000). The Sibley Guide to Birds. Knopf. ISBN 978-0-679-45122-8.
- Sarvasy, Hannah (2016). "Warblish: Verbal Mimicry of Birdsong". Journal of Ethnobiology. 36 (4): 765–782. doi: 10.2993/0278-0771-36.4.765. hdl: 1885/112092. ISSN 0278-0771. S2CID 89990174.
- Baker, Myron C. (2001). "Bird Song Research: The Past 100 years" (PDF). Bird Behavior. 14: 3–50.
- Bailey, C. E. G (2008). "Towards an Orthography of Bird Song". Ibis. 92: 115–131. doi: 10.1111/j.1474-919X.1950.tb01739.x.
- Borror, Donald J.; Reese, Carl R. (1953). "The Analysis of Bird Songs by Means of a Vibralyzer" (PDF). Wilson Bulletin. 65 (4): 271–276.
- Thorpe, W. H. (1958). "The learning of song patterns by birds, with especial reference to the song of the chaffinch Fringilla coelebs". Ibis. 100 (4): 535–570. doi: 10.1111/j.1474-919X.1958.tb07960.x.
- Slater, P. J. B. (2003). "Fifty years of bird song research: a case study in animal behaviour". Animal Behaviour. 65 (4): 633–639. doi: 10.1006/anbe.2003.2051. S2CID 53157104.
- Robbins, Chandler S.; Bertel Bruun; Herbert S. Zim; Arthur Singer (1983). A Guide To Field Identification: Birds of North America. Golden Field Guides (Second ed.). Western Publishing Company. p. 14. ISBN 978-0-307-33656-9.
- Meijer, P.B.L. (1992). "An Experimental System for Auditory Image Representations". IEEE Transactions on Biomedical Engineering. 39 (2): 112–121. doi: 10.1109/10.121642. PMID 1612614. S2CID 34811735.
- "US Patent. 20030216649. Audible output sonogram analyzer". Freepatentsonline.com. 2003-11-20. Retrieved 2014-06-03.
- Alström, P.; Ranft, R. (2003). "The use of sounds in avian systematics, and the importance of bird sound archives". Bulletin of the British Ornithologists' Club. 123A: 114–135.
- Alström, P. (1998). "Taxonomy of the Mirafra assamica complex" (PDF). Forktail. 13: 97–107. Archived from the original (PDF) on 2008-03-07.
- "App - Bird Song Id USA: Nature Apps - Sunbird". sunbird.tv. Archived from the original on 2016-08-04. Retrieved 2016-06-08.
- Munford, Monty (2015-03-28). "Don't know birdsong? There's a (great) app for that". Telegraph.co.uk. Retrieved 2016-06-08.
- Collias, N. E. (1987). "The vocal repertoire of the Red Junglefowl: A spectrographic classification and the code of communication". The Condor. 89 (3): 510–524. doi: 10.2307/1368641. JSTOR 1368641. S2CID 87662926.
- Evans, C. S.; Macedonia, J. M.; Marler, P. (1993). "Effects of apparent size and speed on the response of chickens, Gallus gallus, to computer-generated simulations of aerial predators". Animal Behaviour. 46: 1–11. doi: 10.1006/anbe.1993.1156. S2CID 53197810.
- Hailman, Jack; Ficken, Millicent (1986). "Combinatorial animal communication with computable syntax: Chick-a-dee calling qualifies as "language" by structural linguistics". Animal Behaviour. 34 (6): 1899–1901. doi: 10.1016/S0003-3472(86)80279-2. S2CID 53172611.
- Pepperberg, I.M. (2000). The Alex Studies: Cognitive and Communicative Abilities of Grey Parrots. Harvard University Press.
- Marcus, Gary F. (2006-04-27). "Language: Startling starlings". Nature. 440 (7088): 1117–1118. Bibcode: 2006Natur.440.1117M. doi: 10.1038/4401117a. PMID 16641976. S2CID 14191866.
- Young, Jon (2008). "Bird Language: Exploring the Language of Nature with Jon Young". OWLink Media. Archived from the original on 2010-07-28.
- Birds Can Tell Us a Lot about Human Language Adam Fishbein, February 2, 2018 ( Scientific American)
- Birds use language like humans joining calls together to form sentences, March 8, 2015 The Daily Telegraph (First published in Nature Communications)
- "Archive Pioneers - Ludwig Koch and the Music of Nature". BBC Archives. BBC. 2009-04-15. Retrieved 2 September 2011.
- Matthew Head (1997). "Birdsong and the Origins of Music". Journal of the Royal Musical Association. 122 (1): 1–23. doi: 10.1093/jrma/122.1.1.
- Clark, Suzannah (2001). Music Theory and Natural Order from the Renaissance to the Early Twentieth Century. Cambridge University Press. ISBN 978-0-521-77191-7.
- Reich, Ronni (15 October 2010). "NJIT professor finds nothing cuckoo in serenading our feathered friends". Star Ledger. Retrieved 19 June 2011.
- Taylor, Hollis (2011-03-21). "Composers' Appropriation of Pied Butcherbird Song: Henry Tate's "undersong of Australia" Comes of Age". Journal of Music Research Online. 2.
- Rothenberg, David (2005). Why Birds Sing. Allen Lane.
- Motion, Andrew (10 December 2005). "In full flight". The Guardian. Retrieved 24 April 2016.
- "Why Birds Sing". British Broadcasting Corporation (BBC Four). 1 November 2010. Retrieved 24 April 2016.
- Underwood, Emily (15 August 2016). "Birdsong Not Music, After All". Science. Retrieved 24 April 2016.
- Baptista, Luis Felipe; Keister, Robin A. (2005). "Why Birdsong is Sometimes Like Music". Perspectives in Biology and Medicine. 48 (3): 426–443. doi: 10.1353/pbm.2005.0066. PMID 16085998. S2CID 38108417.
- Taylor, Hollis (2017). "Is Birdsong Music? Outback Encounters with an Australian Songbird". Indiana University Press. Retrieved 2017-06-25.
- Tierney, Adam T.; Russo, Frank A.; Patel, Aniruddh D. (2011). "The motor origins of human and avian song structure". Proceedings of the National Academy of Sciences of the United States of America. 108 (37): 15510–15515. Bibcode: 2011PNAS..10815510T. doi: 10.1073/pnas.1103882108. PMC 3174665. PMID 21876156.
- Attar, Farid al-Din (1984). Darbandi, Afkham; Davis, Dick (eds.). The Conference of the Birds. Penguin Classics. ISBN 978-0-14-044434-6.
- Brooks, Cleanth; Warren, Robert Penn (1968). Stillinger, Jack (ed.). The Ode to a Nightingale. Keats's Odes. Prentice-Hall. pp. 44–47.
- Sandy, Mark (2002). "To a Skylark". The Literary Encyclopedia. Retrieved 22 April 2016.
- "Crow - The Ted Hughes Society Journal". The Ted Hughes Society. 2012. Archived from the original on 2 July 2015. Retrieved 22 April 2016.
- Hopkins, Gerard Manley (1985). Poems and Prose. Penguin Books. ISBN 9780140420159.
|Wikimedia Commons has media related to Sounds of birds.|
- Avian Vocalizations Center Michigan State University
- The Nature Explorers Audio and video of Western North American birds.
- Bird Language: Exploring the Language of Nature with Jon Young A blog with stories and tips for learning the patterns in bird vocalizations.
- Large collection of audio bird calls collected in Arizona from Ask A Biologist.
- xeno-canto: Community online database of downloadable bird sounds from around the globe ≈250,000 recordings of ≈9400 species as of Aug 2015. See also xeno-canto.
- British Library's archive of bird sounds representing more than 8,000 species.
- The Sound Approach A guide to understanding bird sound.
- Listen to Nature includes article "The Language of Birds"
- Bird language articles
- Bird songs in movies: an unnatural history Humor piece on soundtrack errors
- How do Birds Sing? The mechanics and anatomy of birdsong production
- Song Bird Science Shared resource for birdsong scientists
- Bioacoustic Research Program at the Cornell Lab of Ornithology distributes a number of different free birdsong synthesis & analysis programs.
- Macaulay Library at the Cornell Lab of Ornithology is the world's largest collection of animal sounds and associated video.
- Audio Pitch Tracer Accurate transcription of clean recordings of bird vocalizations to midi
- Sonogram Visible Speech GPL Licensed freeware for the Spectrogram extraction.