What Animal Likes to Sing by Whistling When Content
What Animal Likes to Sing by Whistling When Content
PLoS 1. 2022; xvi(9): e0256613.
Cockatiels sing human music in synchrony with a playback of the melody
Yoshimasa Seki
Department of Psychology, Aichi University, Toyohashi, Japan,
Brenton Chiliad. Cooper, Editor
Received 2022 May five; Accepted 2022 Aug x.
- Supplementary Materials
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S1 Movie: Singing in synchrony with human whistling by the birds. Example showing that birds C and PY spontaneously joined the music in the middle and synchronized to alive whistle sounds produced by the experimenter (This pic is presented as an instance and the songs were not used for the analyses in the Results).
(MP4)
GUID: FB0CCEA8-D175-49E0-A996-86FC83B06DEA
S2 Flick: Other vocal imitation past the birds. Example sounds and the spectrograms showing that birds spontaneously imitated not only the tune, simply too several human words. For example, the birds oft vocalized their own name.
(MP4)
GUID: 03AC8FB8-C5BC-4714-8B57-3DA6605C6A19
S3 Movie: Song development of the birds. By < 100 dph, the birds had already started producing vocal sequences which had like characteristics to the model, at least to human listeners. The vocalizations gradually became more similar to the model sound, and by < 220 dph, the vocalizations could be conspicuously recognized by man observers as imitations of the model sounds.
(MP4)
GUID: B96BFDFF-9B2B-4BDC-B47D-0BF79571F0D8
S4 Movie: Imitation of the melody past the birds. Instance sounds and the respective spectrograms demonstrating fake of the melody past the birds (the sound sources used to brand Fig iv and S4 Picture show are identical).
(MP4)
GUID: 50323EE4-BB9E-4A4C-B614-01BFA3574EEC
S5 Movie: An example of unmarried channel recording. Another example of a sound sequence and the corresponding spectrogram showing singing in unison by bird PY (and live whistling by the experimenter). This was recorded from a single channel. Singing starts from the second half of the tune. Due to overlap of the two signals, information technology is hard to separate song signals produced by the bird from the whistle sounds produced by the experimenter. Although a number of these types of recordings (both with live operation and with playbacks) were obtained, these information were not used for the analyses in the Results section due to the difficulty in separating the two signals.
(MP4)
GUID: 802B59F2-D079-4826-BDCF-BE1D16E7FBED
S1 File: This file includes all audio spectrograms used in the analyses. (PDF)
GUID: 4BD01AD4-DB87-4189-9E7F-8A41CF20CC5A
- Data Availability Argument
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All relevant data are within the manuscript and its Supporting Information files.
Abstract
It is known among aviculturists that cockatiels imitate human being music with their whistle-like vocal sounds. The present written report examined whether cockatiels are also able to sing "in unison", or, line upward their vocalizations with a musical tune and then that they occur at the aforementioned time. 3 manus-raised cockatiels were exposed to a musical tune of human whistling produced by an experimenter. All the birds learned to sing the melody. Then, two out of these three birds spontaneously joined in singing during an ongoing melody, so that the singing by the bird and the whistling past the human were almost perfectly synchronous. Further experiments revealed that the birds actively adjusted their song timing to playback of a recording of the same melody. This means cockatiels have a remarkable ability for flexible vocal control similar to what is seen in homo singing. The proximate/ultimate factors for this behavior and implications for musicality in humans are discussed.
Introduction
Humans have a large variety of circuitous songs and instrumental music, which makes human "musicality" special. Hither, musicality is defined as the fix of capabilities and proclivities that allows our species to generate and bask music in all of its diverse forms [1] and encompasses the underlying biological capacities that let us to perceive and produce music [2]. In addition, singing along to an ongoing melody of familiar music is also widely seen in people. For example, at a birthday political party when one person initiates the vocal "Happy Altogether", information technology is like shooting fish in a barrel for people to follow along [3], or to sing in unison (i.e., multiple individuals singing a single audio-visual pattern in synchrony, not merely a temporal overlap of vocalizations produced past multiple individuals). Even so, singing in unison requires controlling outputs from the song organs to match both the timing and the spectral patterns of an ongoing sound stream; i.e., temporal and spectral synchronization [4]. That is not all. Musical melodies are non innately programmed into our vocal repertoires; thus, to join in an ongoing melody, it is necessary to encode and store the global structure of the melody in memory. Then, at the onset of singing, the singer must choose the appropriate starting note from retention instantaneously in order to coordinate vocal outputs along the sound stream. Therefore, complicated cognitive mechanisms should be involved in singing a musical melody in unison.
So, the question here is whether non-human animals are capable of showing a similar behavior. Equally described beneath, a few species sing songs imitating human music and even fewer animal species vocalize in unison. However, no written report has reported these ii capabilities exhibited together in not-man animals, to my cognition. The present study demonstrates that cockatiels are able to imitate the melody of (a) human music and are able to sing it (b) in unison (c) spontaneously (d) with playback of recorded sounds performed by a human being (i.due east., not conspecifics) (east) in a context apart from reproduction. To underscore the significance of the results, some relevant points are introduced in the post-obit paragraphs.
Faux of man music by non-human animals
Some non-human animals, such as songbirds, can add novel acoustic patterns to their own vocal repertoires by listening to sounds [5, 6]; they are considered vocal learners. Withal, in most song learning animals, the innate constraints for incorporating novel sounds is much stricter than in humans. For example, juvenile finches learn songs from their father very well; nevertheless, they copy songs imperfectly when the tutor is a foster father of a unlike species [7, viii]. Therefore, it makes sense that virtually animals do not imitate melodies of human being music.
Some vocal learning animals imitate human speech and/or bogus sounds. The African grey parrot, Alex [nine], and the harbor seal, Hoover [10], may be the well-nigh famous examples. More than recently, a study reported that an elephant produced man spoken language sounds [11]. Some song learning animals as well imitate various artificial sounds. Lyrebirds imitate the noises of a chainsaw [12], for case. However, human music has unique qualities autonomously from spoken communication and other bogus sounds; music has harmonic syntax, rhythmic syntax, and is characterized by meter, grouping and hierarchy. Some of these qualities are shared in common with linguistic communication, merely not all of them [13]. Thus, the cerebral processes involved in musicality should differ from those used in the perception and product of other types of audio sequences, including human speech. Moreover, it is plausible that the audio-visual structure of human being music is quite different from the acoustic construction of natural animal vocalizations. Thus, musical melodies may be suitable imitation models for evaluating the flexibility of cognitive processing involved in vocal learning in animals. Therefore, investigating whether animals can imitate human music may be an interesting enquiry theme, and may provide more insight for further understanding of their cognitive capabilities, beyond whether they can imitate human speech and/or artificial noises.
Anecdotally, many videos have been uploaded to online databases (such every bit YouTube) by aviculturists, in which cockatiels imitate melodies of human music with their whistle-like vocal sequences. Examples include the "Mickey Mouse Social club March" and the theme vocal of "My Neighbor Totoro". However, there are simply a few bookish publications describing false of human music past animals. Ane report showed that bullfinches imitated human music and sang the melody alternately with whistling produced by an experimenter [14]. Further, it was documented that a European starling named Kuro sang some melodies of human music [15]. Another study reported that gray seals learned to modify their vocalizations to match the frequency patterns of musical melodies that were composed of human vowel-like sounds under an operant conditioning paradigm [xvi] (annotation: in these studies, animals did not sing in unison). In sum, further academic documentation of music production by animals would exist valuable for comparative approaches in relevant inquiry fields, such equally neuroscience, cognitive studies, and psychology.
Singing in unison by non-human animals
Many animals, including non-song learners and fifty-fifty invertebrates, sing songs together, forming duets or choruses [17]. As an example, howling by wolves results in audio-visual patterns that form a heterophony [3]. Equally another example, two gibbons generate nifty calls together with the vocal timing of one individual likely depending on that of the other [18–20]. In addition, many studies documented songbirds singing together [21]. Songbirds are song learners; thus, singing together in songbirds is much more relevant to the present topic than similar behaviors in non-song learners. However, studies demonstrating singing in unison or, monophony (as opposed to but singing at the same fourth dimension) by non-human animals are quite rare, including those in songbirds. Likely, this is one reason why one author stated that "human beings are the just species to have evolved the ability to sing in unison in both the dimensions of rhythmic co-ordination and precise pitch attunement" [22]. As a thing of fact, it is known that a few avian species practise sing in unison. Male and female mates of the forest weaver sing in unison, which were probable derived from a territorial display [23, 24]. White-browed sparrow weavers also sing in unison [25]. Lastly, male person and female person plain-tailed wrens sing duets antiphonally, only occasionally males and females sing songs in unison with near perfect synchrony [26–28]. In mammals, recently, a report reported that two male dolphins occasionally produced isochronous pop sound sequences in synchrony [29], which is likely the only academic report of non-human mammals vocalizing in unison thus far. However, this behavior is much simpler than the singing in unison performed by humans.
In sum, the examples of singing in unison past non-man animals reported in these studies were (i) only between conspecifics, (ii) occurred in specific contexts involving reproduction (including territorial defence), and (iii) used merely vocal variations observed in the wild (the vocal system is optimized to use those sounds, making the beliefs relatively easy; on the contrary, learning and producing a melody of man music may crave much larger costs for the song arrangement as described in a higher place). Therefore, the present written report would provide further cognition to empathise the similarities and differences seen between humans and not-human animals with regard to musicality.
Introduction for the experiment
A research project was launched to investigate musicality in non-human animals. Cockatiels were chosen as the subjects because it is well known that they sing melodies of human music as described higher up. In the project, 3 mitt-raised cockatiels learned to sing a marching audio: whistling of a melody similar to the "Mickey Mouse Club March" produced by a human (the experimenter). The melody was composed of the 2 parts; the beginning half (consisting of 11 notes) and the second half (consisting of eleven notes) separated past a long pause (640 ms, run into Materials and Methods). Then, ii of the birds (bird C and bird PY) spontaneously sang in unison with the whistling (meet S1 Movie). Therefore, the following two experiments (with some predictions) were carried out to examine whether the birds would actively synchronize their vocalizations with a playback of a recording of the melody.
Experiment 1
A playback sequence is presented while a bird is singing to notice how the bird would modulate his vocal timing.
Prediction I
If a bird actively synchronizes his vocal timing to the playback sound, he will practise so past lengthening the duration of the long pause between the first one-half and the second half. This long pause between the halves of the tune provides a good opportunity for the bird to arrange his song timing with the playback sound sequence. If the delay between the bird'south singing and the showtime of the playback increases, the bird will compensate by also increasing the duration of the break between the two melody halves.
(Culling) If the elapsing of the long pause remains the same regardless of the playback filibuster, the fourth dimension difference betwixt the playback and singing will be maintained until the end of the melody. This suggests that the bird did not actively synchronize to the melody.
Experiment 2
A playback sequence is presented when a bird is not singing to detect whether the bird begins to sing following the playback, and how he modulates his song timing to synchronize with the playback of the tune.
Prediction 2
If the bird begins to sing post-obit the playback, he will start singing in the eye of the tune at whatsoever fourth dimension point along the ongoing sound sequence, synchronizing his vocal timing with the playback. As a result, the song will be an irregular sequence because it lacks some of the initial notes.
(Alternative) If the bird ever starts singing from the beginning of the vocal, even when the playback has already advanced past this signal in the melody, it suggests the bird ignored the playback sound and did not synchronize his song to the playback tune.
Prediction Three
If the bird begins to sing following the playback and begins the song from the initial note (instead of the eye of the tune as in Prediction II), the song is slightly delayed from the playback melody. Therefore, if the bird actively synchronizes to the melody, he may skip some of the latter notes in the first half in society to conform his vocal timing to the playback at the onset of the second one-half of the melody. This will besides result in an irregular song sequence. While there are other ways in which the bird could adjust his vocal timing (e.yard., singing the unabridged first half and shortening the duration of the interruption between melody halves; however, this requires reducing a period of rest and rushing to vocalize the second half of the tune. So, this strategy is not likely), this is a likely scenario.
(Alternative) If the song sequence is unchanged, and all notes are present, it suggests the bird ignored the playback sound and did not synchronize his song to the playback melody.
In the experiments, both playback sounds and vocal sounds of the birds were simultaneously recorded to analyze whether the birds sang every bit predicted.
Results
Experiment 1: A playback sequence was presented while a bird was singing
Using the updated recording system (see Materials and Methods), seven recordings were obtained from bird C (C#1 − C#vii in Supplementary Information; hereafter, S1 File ) and v recordings were obtained from bird PY (PY#1 − PY#5 in S1 File ), in which the birds kept singing afterwards the playback sounds were presented. The birds changed the intermission elapsing of their own song (consistent with Prediction I ). The actual onset of the second half of singing was delayed from the putative onset (the original playback sound was used every bit a standard reference to measure the delay; see Fig 1A upper and S1 File ). The delay in singing (Y; indicated by green shading in Fig 1A ) depended on the latency of the playback (X; indicated by yellowish shading in Fig 1A ). The duration of Y was longer when Ten was longer ( Fig 1B ). There was a significant correlation between 10 and Y (r = 0.972 [95% CI = 0.899 − 0.992], t = 12.975, df = 10, p < 0.001; individual results are also shown in S1 File ). These results indicate that the birds actively adapted their vocal timing to the playback sound.
Effects of playback sounds on ongoing singing.
These recordings were obtained from bird C (the same recordings are shown as C#3, C#4 and C#6 in S1 File ). Model sounds (Atomic number 82: playback, pink shading) were played back after the bird began singing (Vo.: blue shading). Yellow shading indicates the latency of the playback audio (X). Green shading indicates the duration between the onset of the second half of the standard reference (see main text) and the actual onset of the second half of singing (Y). Note that the onset of the second half of the playback sound and the singing started at nearly the same fourth dimension (A). Correlation betwixt the length of X and the length of Y is shown in Fig 1A. Each dot denotes values of X and Y obtained from a recording that includes bird singing and playback of the tune. When the length of Ten is longer, the length of Y is longer (B).
Experiment 2: A bird began to sing post-obit the presentation of a playback sequence
Bird C did non begin to sing following the presentation of a playback sequence. However, 15 recordings were obtained from bird PY, in which the bird sang songs following the presentation of playback sounds (PY#half dozen − PY#20 in S1 File ). In 1 out of the xv recordings, the bird sang the normal sequence of the tune with some irregular notation intervals, as if he was trying to ignore the playback audio; then, he stopped singing in the middle of the 2d half (PY#eighteen in S1 File ). In 2/15 recordings, the bird sang a express part of the first one-half and so stopped singing all of a sudden (PY#19 and PY#twenty in S1 File ). Yet, in 9/15 recordings, the bird started singing and synchronized his vocal timing with the playback, either from the beginning of the 2nd half by skipping the entire beginning half (5/xv recordings; Fig 2A ; PY#6 − PY#x in S1 File ), or from the centre of the first half by skipping several (between ane and 6) initial notes (four/15 recordings; Fig 2B ; PY#xi − PY#14 in S1 File ). Both of these adjustments are consistent with Prediction Ii . The bird occasionally sang songs spontaneously during the experimental period, then 46 song recordings were obtained without the playback audio. In these recordings, the bird always began singing from the beginning of the first half and never started in the heart of the melody (0/46 recordings), indicating that any aberrant singing observed was not caused by run a risk, but was in response to the playback sound (p < 0.001, Fisher's exact test).
Examples of singing in response to playback sounds.
These recordings were obtained from bird PY. Starting from the 2d half (A; the same recordings are shown equally PY#six and PY#10 in S1 File ). Starting from in the middle of the starting time half (B; the aforementioned recordings are shown equally PY#12 and PY#13 in S1 File ).
In 5/15 recordings, bird PY started singing from the beginning of the sequence with a slight delay following a playback sound (PY#xv − PY#19 in S1 File ). Each time, the latency was roughly the aforementioned value (hateful = 243.nine ms, SD = 20.99 ms). Therefore, it is possible that these v songs were triggered by the get-go note of the playback sound. While the bird stopped singing in the centre of the normal song in ii out of the five recordings (PY#18 and PY#19 in S1 File ), he sang the song to the end in 3/5 recordings ( Fig three ; PY#15, PY#16 and PY#17 in S1 File ). Still, in these iii recordings, the last two notes of the outset half were dropped and the songs were resumed at the onset of the second half, which did not happen when the bird was singing without the playback (0/46). Thus, it is likely that this behavior did not only occur by take a chance (p = 0.029, Fisher's exact test), suggesting the bird actively skipped those ii notes to synchronize his vocal timing with the playback at the kickoff of the second half. This aligning is consistent with Prediction III .
Examples of irregular vocal sequences with playback of the melody.
These recordings were obtained from bird PY (the aforementioned recordings are shown every bit PY#15, PY#16 and PY#17 in S1 File ). The vocalizations began following the playback (indicated by blackness arrows) and the last 2 notes of the first half were dropped (indicated by red circles).
In Experiment two, at that place were several examples in which Bird PY began to sing post-obit the playback and it is possible that the bird entrained to the ongoing tune. If this is the case, then for the 12 recordings which were consequent with our predictions (9 songs for Prediction Two and three songs for Prediction III) we might see a negative mean asynchrony (NMA). Information technology is well known that when humans create a series of motor outputs synchronizing with a rhythmic stimulus, their motor outputs tend to slightly precede each stimulus presentation, which is termed NMA [xxx]. Also, NMA is considered one indication that animals have entrained to a rhythmic sequence [31]. To examine this possibility, the timing of the vocalization at the onset of the second half was compared to the timing of the playback at the onset of the second one-half. The results showed that singing started slightly only significantly faster than the playback (hateful -135 ms, median -94 ms; V = 8, p = 0.012, Wilcoxon signed rank examination [the null hypothesis; mu = 0]), which tin be interpreted as an NMA. This upshot also supports the interpretation that the bird actively synchronized his song timing with the playback.
Discussion
The results betoken that the cockatiels actively synchronized their vocal timing with the playback of the melody of human being music. As described in the Introduction, faux of human music was previously reported in only a few non-homo fauna species. Likewise, academic reports for singing in unison by not-human animals are rare. Therefore, this is the first instance, to my cognition, of vocal functioning by non-human being animals combining these 2 abilities (singing a melody of homo music and synchronizing to a model audio). In improver, the cockatiels sang spontaneously with a non-conspecific animal (i.e., a human), without food rewards, and in a non-reproductive context. Given these conditions, it is likely that this experimental demonstration can provide some novel insights for this field of research. In add-on, the results suggest the cockatiels' ability for processing a series of complex neural commands; that is, they are able to memorize the whole melody, decide where the notation is located within the ongoing melody, and then control their song outputs with precise timing. Yet, it is important to state that the nowadays study did not examine the capability of the birds to attune spectral patterns in response to frequency-altered playback of the model sound (i.e., spectral synchronization), which would exist an interesting challenge for future study.
Why do cockatiels sing in unison?
To obtain an answer to this question, we can plow to previous studies investigating the song behavior of wild parrots, but there are only a few studies. Duets between conspecifics (sung in antiphony, non in unison) take been reported in wild Greyness-headed parrots [32] and Yellowish-naped amazons [33]. The duets of Xanthous-naped amazons are produced by a male and female pair, which are sung for articulation territory defense [34]. However, the behavioral contexts in which these wild parrots sing duets differ from the contexts for singing in unison by the cockatiels in this report.
As some authors described, studying the vocal learning of parrots in the wild is difficult due to several reasons: they stay high up in the canopy, move in and out of the foliage, and do not generally stay in one place for long periods of time [35, 36]. Thus, there are also currently no academic reports of song learning in wild cockatiels, to my knowledge. Moreover, in that location are few laboratory studies examining the vocal behavior of cockatiels, most of which describe only their short calls, and not songs [37–41]. As i exception, an author described that captive cockatiels oft produced complex, long-lasting vocalizations which might appear to qualify as song [42]; however, the author did not draw the acoustic details or the function of these vocalizations. Information technology is known amid aviculturists that convict cockatiels often imitate human speech communication, music and other sounds; however, information technology is unclear whether cockatiels sing songs in the wild or not (and consequently, even if they do, the role is unknown). To the contrary, budgerigars very frequently sing warble songs. It is assumed that the songs are used for bonding amid social companions, private / group recognition, and as a bluecoat of group membership [43]. Therefore, the speculation that cockatiels sing in unison for social bonding may be valid. Anecdotally, the cockatiels in this study often sang the musical sounds or imitated human being speech when caregivers were leaving the aviary. Therefore, they may take done and then to attract attending from humans, though in that location is no quantitative data to support this observation. This is consistent with the music and social bonding hypothesis [2]. This idea is besides supported by the fact that no nutrient reinforcements were necessary for the birds to sing in unison. We may think about another related question. The bullfinches [14] and European starling Kuro [fifteen] described in the Introduction were paw-reared, as were the cockatiels in the present written report. Therefore, these birds might recognize their human being caregivers as their own conspecifics, and might recognize human music as vocalizations produced past conspecifics. As a outcome, they might acquire the melodies in the aforementioned mode as many songbirds acquire songs from conspecifics. On the opposite, it is also possible that the birds learned the tune even though they recognized their human being caregivers as heterospecfic animals and considered the melodies to be heterospecific vocalizations. However, there is currently a lack of quantitative data enabling further discussion of these possibilities. Nosotros must wait until the points described above have been tested experimentally.
How exercise cockatiels sing in unison?
Auditory-vocal mirroring in the neural circuit involved in vocal production and vocal learning in songbirds may partially explicate the substrates for this behavior. Some neurons in the nucleus HVC (proper name, not an abbreviation) are activated not only when a bird produces a particular vocal note simply too when the bird listens to the same vocal annotation [44]. Parrots take a neural excursion for vocal production and vocal learning similar to songbirds that contains the nucleus NLC (central nucleus of the lateral nidopallium) which corresponds to the songbird HVC [45]. Therefore, it is valid to speculate that some neurons involved in the production of the melody were too activated when birds listened to the playback of the melody as if the cockatiel was singing. The neural activeness elicited from listening might lead to singing of the melody. Thus, the present findings may exist a behavioral demonstration suggesting parrots have a neural system for auditory-vocal mirroring like to songbirds. Another recent study recorded neural action of HVC neurons in songbird pairs during duet singing. The authors reported that the degree of interindividual synchronization of neural activity was positively correlated with the degree of interindividual synchronization of vocal action during alternating parts of duet bouts [46]. Therefore, the activity of NLC in cockatiels might be involved in the timing control of singing in unison.
Further, parrots have additional structures in their vocal learning nervous system which may exist involved in this beliefs. The parrot vocal nuclei have cadre regions and shell regions. Connections between the cores and shells are sparse within and among each vocal nucleus. Cores tend to project to cores, and shells tend to project to shells. This results in two parallel systems: a core organisation and a shell organisation [47]. The neural connectivity of the core vocal nuclei is similar to that of the song nuclei of songbirds, whereas the crush system is unique to parrots. The unique arrangement may allow for more circuitous vocal communication abilities and greater auditory–motor entrainment than in other birds [48].
In add-on, parrots may have excellent neural and psychological substrates to synchronize their motor outputs to external rhythmic stimuli. The cockatoo, Snowball, spontaneously showed entrainment through trip the light fantastic to various beats of human music [49], which was considered the get-go sit-in of this type of behavior past non-human animals. Other studies trained budgerigars to synchronize to metronomic sounds using operant conditioning techniques [31, fifty]. While the impact of these budgerigar studies are less than that of the Snowball study, the results support the idea that some parrot species have an excellent capability for entrainment. Rhythmic entrainment should be ane of the important factors required for singing in unison; thus, the neural and psychological substrates for rhythmic synchronization of body movements may accept a linkage to that for rhythmic synchronization of vocalizations, at least in parrots.
In addition, some recent studies suggest that parrots may have some farther capabilities involved in musicality. Snowball originally created diverse motor patterns for dancing that were performed with musical melodies [51]. A study reported that an African grey parrot was trained to produce a vocal sequence following a sound sequence produced from a piano. Each sequence produced past the bird followed musical rules similar to the previous piano sequence in terms of the frequency ratios between the notes [52]. Another report showed that wild palm cockatoos can make drumming sequences with regular intervals using several tools [53]. Moreover, a recent report reported that cockatiels manipulated several objects producing sounds [54]. The substrates for singing human music in unison by cockatiels may too exist relevant to these behaviors.
Implications of singing in unison past non-human animals for understanding musicality
Modernistic human society is full of music. Nosotros often mind to music and play music in diverse situations apart from sexual and reproductive contexts. Nevertheless, it does not mean that people find just whatsoever complex sound sequence pleasing to the ear. Humans accept a preference for the structure of musical sounds, such as harmonic intervals (or, consonance). The harmonic intervals used in music are mostly consistent across dissimilar cultures [55]. In consonant melodies (e.g., consisting of minor and major thirds [56]), pitch classes often reflect small-integer frequency relationships (in the above example, minor and major thirds are 5:half-dozen and 4:5 frequency ratios, respectively) and unison makes the simplest frequency ratio (i.e. i:one) [2]. Therefore, while cockatiels are singing in unison, they are creating a consonant melody with their vocalizations. Here, nosotros tin can consider the question of why some non-human fauna species prefer consonance while other species do not [56–58]. The song similarity hypothesis [55] suggests that, in humans, the preference for consonance in music may originate from its similarity to the acoustical structure of their vocalisation. Further, non-human animals are likely to utilize relative pitch to identify harmonic information that is similar to their own vocalizations [59]. From this perspective, it is valuable to investigate whether there is a preference for consonant sounds in the cockatiels, because they spontaneously created a consonant melody while singing in unison. Thus, if they prefer consonant sounds, it may support the vocal similarity hypothesis. Additionally, aligning acoustic spectra tin can promote bonding in humans (e.g., people would get along with each other through singing in a chorus group or playing instruments in a band/orchestra) [2]. So, cockatiels singing in unison with human whistling may be involved in social bonding (i.e., creating social relationships between cockatiels and humans). Lastly, in singing in unison, cockatiels probable prefer to imitate human music performed with whistle sounds rather than man speech, even though they can imitate various human speech sounds. Thus far, I take never observed cockatiels "talking" in unison with man speech sounds. This might be consistent with the argument that the processing of pitch information differs significantly for voice communication and music in humans [sixty]. Equally some other possibility, when cockatiels vocalize in unison, they may prefer the college frequencies used for imitating whistle sounds to the lower frequencies used for imitating human being speech. In any case, altogether, the nowadays findings append farther perspectives on the recent progress in comparative approaches for investigating man musicality [61–66].
Materials and methods
All experimental procedures and housing conditions were approved by the Animal Experiments Committee of Aichi Academy (approving number 15–01). All experiments were performed in accord with the Primal Guidelines for Proper Conduct of Animate being Experiments and Related Activities in Bookish Research Institutions under the jurisdiction of the Ministry of Education, Culture, Sports, Scientific discipline and Technology of Nippon (MEXT).
Subjects
Male person cockatiels were obtained from a local breeder at the age of approximately 25 days mail service-hatch (dph) and were kept in independent cages (370 mm (Westward)× 415 mm (D) × 440 mm (H)) placed in an aviary (25°C, 12:12h photoperiod) at Aichi University. The birds were hand-raised by human caregivers to facilitate the ability to mimic sounds produced by humans and oft heard homo voices; still, the birds were isolated from homo music except the model melody equally much as possible (they might be occasionally exposed to some sounds, such as chimes and sirens, when they were outside their rearing room).
Apparatus
Stimulus sounds (human whistles) and birds' vocalizations were captured with a cardioid microphone (PRO35, Audio-technica, Nihon) and recorded with a PCM recorder (DR-40, Teac, Nihon). Stimulus sounds were presented through a loudspeaker (either AT-SP151 or AT-SP120, Audio-technica) during the playback experiment.
Stimulus
A typical serial of whistle sounds (which was similar to a portion of the "Mickey Mouse Club March"; 8.1s duration, 107 bpm [beats per minute], frequency range: 1100−1950 Hz) produced by the experimenter was recorded every bit a Windows PCM file (.wav format; 44.1 kHz sampling charge per unit) and band-laissez passer filtered (500–4000 Hz) using software (SASLab Pro., Avisoft Bioacoustics, Germany). The sound sequence was used as a template (or, a model) for the faux by the birds. The melody was composed of 22 notes and was divided into two halves (eleven notes each), which were separated by a long pause (640 ms; Fig 4A ). Live functioning of the whistle sounds was ofttimes presented to the birds (see beneath) to facilitate fake. To human ears, the live sounds are nearly identical to the sounds in the recording. More importantly, the two sources of the melody seem to be identical to the birds, because they sang songs similarly in response to both the alive performance (see S1 Movie) and the playback sounds (described below).
Example spectrograms showing imitation by the birds.
The model sound (A) and vocalizations by bird PY (B), by bird C (C) and by bird PK (D). Every bit shown in S3 Movie, the birds learned to imitate the melody stride-by-step. These recordings were obtained soon afterward they began to sing the full melody. PK imitated the music, but did not sing in unison every bit frequently as the other two birds, so this bird did non participate in further experiments of this study.
Vocal learning of the melody
From early in life, three birds were exposed to the whistle audio sequence upward to thirty times per day, either produced live past the experimenter or from a recording of the tune. The birds spent a big portion of each day with humans and were released from their cage for about ane 60 minutes each solar day to play with humans. This was washed to raise their social relationship with humans, which could facilitate mimicry of the tune past the birds. Therefore, it was not viable to keep birds inside an experimental box to tape their vocal development every bit has been done in previous songbird studies [67]. Thus, I do non have a consummate history for the vocal evolution of the birds and vocalizations were only recorded when birds produced sounds of interest (e.g. S2 and S3 Movies).
Song imitation was established without any food rewards, though the human caregivers frequently verbally rewarded the birds for their song behavior (meet S1 Movie). The birds were not trained with any specific methods, such equally the model-rival method [9]. Still, somewhen, the birds were able to imitate the sounds ( Fig 4B–4D , S4 Picture show). Throughout this process, both live performance of whistles by the human and a recording of the whistle sounds played back from a PC ( Fig v , see below) were used in parallel equally the model sounds. A number of songs were recorded in both the live and playback atmospheric condition; however, for the analyses in the Results section, only songs recorded with the playback sounds were used. This method ensures that the stimulus sounds were ever consistent. Therefore, the active adjustment of vocal timing to a playback sound by the birds was quantitatively examined.
A schematic diagram of the updated recording arrangement.
All recordings of singing by the birds used for the analyses in Results department were obtained using this organisation. Therefore, the stimulus sounds presented to the birds were played back from the PC, not live performance by the experimenter.
Initial recordings via a single channel
A number of solo songs from the birds and vocal responses to the playback melody were recorded via the monaural aqueduct of the recorder. In the latter phase of evolution (after the birds were nearly one yr former), the recording began to include a considerable number of songs sung in unison with the melody. Yet, somewhen it was difficult to sufficiently separate the song signals from the playback sounds in the single aqueduct recordings for assay. Nevertheless, human listeners could clearly identify the birds singing in unison (S5 Flick, for example). Therefore, a new recording organisation was built, which immune for more rigorous assay.
Recordings with the updated system
Vocal sounds from the birds were recorded by the left channel of the PCM recorder via the microphone, which was directed toward the subject. The stimulus audio signals were sent out from Windows Media Player on a PC. The output was divided into ii streams via audio connectors. I of those streams was amplified and presented to each bird as the sound stimulus through the loudspeaker (about lx dB at the bird's position) located at the insensitive direction of the microphone; the other was connected direct to the right channel of the PCM recorder. This setup enabled recording of both the birds' vocalizations and the playback stimulus simultaneously and separately ( Fig 5 ). All data shown in the Results section was recorded with this updated system. At that place were no other birds in the recording room, which was kept in silence (the background noise level was about 35 dB) during the experiments. Data used for assay was recorded from each bird at the guess ages of 330 dph (bird C) and 450 dph (bird PY). Recordings took place one−2 hours a day for half-dozen days in total for each bird.
Analyses
Birds' vocalizations were edited and analyzed with SASLab. Depression frequency sounds were cut off with a high-pass filter (0.v kHz). The sound amplitude was normalized to 75% of the dynamic range at the peak amplitude of the sound sequence. The audio spectrograms (FFT length: 512, Temporal resolution: 87.5% overlap) were created and the onset of each note was obtained with a part of the software (Automatic parameter measurement).
Statistics
Statistical analyses were performed using R3.4.1. Functions "cor.exam" with Pearson'south correlation coefficient, "fisher.test" and "wilcox.exact" were used. All tests were performed two-sided.
Supporting information
S1 Moving picture
Singing in synchrony with homo whistling by the birds.
Example showing that birds C and PY spontaneously joined the music in the middle and synchronized to alive whistle sounds produced past the experimenter (This motion picture is presented every bit an example and the songs were not used for the analyses in the Results).
(MP4)
S2 Picture show
Other vocal imitation by the birds.
Example sounds and the spectrograms showing that birds spontaneously imitated not only the melody, simply too several human being words. For example, the birds often vocalized their own name.
(MP4)
S3 Moving picture
Vocal development of the birds.
By < 100 dph, the birds had already started producing vocal sequences which had similar characteristics to the model, at to the lowest degree to homo listeners. The vocalizations gradually became more similar to the model sound, and by < 220 dph, the vocalizations could be conspicuously recognized by human observers as imitations of the model sounds.
(MP4)
S4 Movie
Imitation of the melody by the birds.
Example sounds and the corresponding spectrograms demonstrating imitation of the melody past the birds (the sound sources used to make Fig four and S4 Film are identical).
(MP4)
S5 Movie
An case of single channel recording.
Another instance of a audio sequence and the respective spectrogram showing singing in unison past bird PY (and live whistling by the experimenter). This was recorded from a single channel. Singing starts from the second half of the melody. Due to overlap of the two signals, it is difficult to separate vocal signals produced by the bird from the whistle sounds produced by the experimenter. Although a number of these types of recordings (both with live performance and with playbacks) were obtained, these data were not used for the analyses in the Results section due to the difficulty in separating the two signals.
(MP4)
S1 File
This file includes all sound spectrograms used in the analyses.
(PDF)
Acknowledgments
I give thanks to postdocs and students of the laboratory and C. I. for taking intendance of the birds and providing back up for the experiments.
Funding Argument
YS JP25285198, JP17H01015, JP17H06380 Japan Society for the Promotion of Science https://www.jsps.go.jp/english/index.html The funders had no function in study design, data collection and assay, decision to publish, or training of the manuscript.
Data Availability
All relevant data are within the manuscript and its Supporting Information files.
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What Animal Likes to Sing by Whistling When Content
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