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1

Acoustic structure of bird song

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· Syntax - specific timing and ordering of song elements
· Note
· Element
· Syllable
- Phrase

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2

Acoustic structure of bird song research

Hsu et al. (2018)

3

Hsu et al. (2018)

Investigating the identity, distribution, and evolution of bird species is important for both biodiversity assessment and environmental conservation. The discrete wavelet transform (DWT) has been widely exploited to extract time-frequency features for acoustic signal analysis. Traditional approaches usually compute statistical measures (e.g., maximum, mean, standard deviation) of the DWT coefficients in each subband independently to yield the feature descriptor, without considering the intersubband correlation. A new acoustic descriptor, called the local wavelet acoustic pattern (LWAP), is proposed to characterize the correlation of the DWT coefficients in different subbands for birdsong recognition. First, we divide a variable-length birdsong segment into a number of fixed-duration texture windows. For each texture window, several LWAP descriptors are extracted. The vector of locally aggregated descriptors (VLAD) is then used to aggregate the set of LWAP descriptors into a single VLAD vector. Finally, principal component analysis (PCA) plus linear discriminant analysis (LDA) are employed to reduce the feature dimensionality for classification purposes. Experiments on two birdsong datasets show that the proposed LWAP descriptor outperforms other local descriptors, including linear predictive coding cepstral coefficients, Mel-frequency cepstral coefficients, perceptual linear prediction cepstral coefficients, chroma features, and prosody features. Furthermore, the proposed LWAP descriptor, followed by VLAD encoding, PCA plus LDA feature extraction, and a simple distance-based classifier, yields promising results that are competitive with those obtained by the state-of-the-art convolutional neural networks.

4

Song dialects in different populations of white-crowned sparrows (Marler & Tamura, 1962)

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5

Song dialects in different populations of white-crowned sparrows (Marler & Tamura, 1962) research

Baptista and Kind (1980)

6

Marler and Tamura (1962)

The phenomenon of "dialect" variation in bird song, appearing as a consistent differ- ence in the predominant song type between one population and another of the same species, has a special interest for biologists, serving as a focus for attention in discus- sion of such diverse topics as speciation (for example, Huxley, 1942; Mayr, 1942), learning (Thorpe, 1954, 1958) and the mechanisms of social communication (Marler, 1959). The White-crowned Sparrow (Zonotrichia leucophrys) affords one of the best known cases of such "dialect" variation among North American birds, and it has been commented upon by many who have observed this species (Blanchard, 1941; Peterson, 1941). Before the ontogenetic basis of such local song variation can be assessed and before its evolutionary significance can be satisfactorily determined, careful descrip- tions of the nature and extent of the variation are required. This paper seeks to provide some of this necessary information by describing song variation in the individual and in a population, both at one time and from year to year, and also by comparing songs in three populations, two adjacent and one distant

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Baptista and Kind (1980)

We sampled the songs of 18 populations of montane Whitecrowned Sparrows (Zonotrichia leucophrys oriantha)in order to define their dialect groups, if any, and to explore vocal affinities with other western subspecies of Z. leucophrys. We found a clear-cut regional differentiation of song primarily on the basis of syllabic morphology and secondarily on the sequence of elements in the song. The birds of the Sierra Nevada and the San Bernardino Mountains of California constitute a fairly homogeneous dialect group related to another distinct group in the Warner Mountains, California, which are separated from the Sierra Nevada to the north by habitat unsuited to breeding oriantha. Those in two nearby but isolated desert ranges share a unique song type resembling that of Z. l. gambelii. Oriantha in the Wallowa Mountains, Oregon, to the northeast of the Steens Mountains, are allied with the dialect region of the northern Rocky Mountains. Syllabic morphology and the sequence of song elements also suggest certain vocal affinities of oriantha with other western subspecies of Z. leucophrys. For instance, the songs of oriantha in the Sierra Nevada, Warner Mountains, and San Bernardino Mountains have elements in common with those of nuttalli in central California and pugetensis north of the Columbia River. The songs of oriantha at Hart Mountain and in the Steens Mountains are very similar to those of gambelii in Alaska and the western Canadian Rockies. The songs of oriantha in the San Bernardino Mountains (a population founded after 1907)are identical with those of the central Sierra Nevada, and thus trace the origin of the founding group. We postulate that these and other data are consistent with Rand's interpretation of the subspecific differentiation of these sparrows in Pleistocene refugia
 

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Isolated young white-crowned sparrows distinguish and learn their own-species song from tape tutors (Gould and Marler, 1987)

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Young males recognise and learn species-specific songs played along with several songs from other species

9

Isolated young white-crowned sparrows distinguish and learn their own-species song from tape tutors (Gould and Marler, 1987) research

Peters and Nowicki (2017)

10

Peters and Nowicki (2017)

Most songbirds learn their songs through imitation. However, what a male sings as an adult is not necessarily a complete inventory of what he memorized at some earlier point in time: songbirds commonly memorize more material than they eventually sing as adults. Work with swamp sparrows, Melospiza georgiana, first confirmed that males rehearse many of the song models to which they are exposed during the sensory phase of song acquisition but subsequently include only a subset of those rehearsed songs in their adult repertoire. This process of overproduction and selective attrition has since been demonstrated in other species as well. More recently, the persistent memory of tutor songs rehearsed but not included in the adult repertoire has been demonstrated at the neural level. Furthermore, memories of song models heard during the sensory phase of acquisition but never detected during rehearsal in the sensorimotor phase also may persist into adulthood. Here we review behavioural and neural studies of overproduction and attrition in song learning. We discuss factors that may trigger the persistence of some models and the rejection of others in an individual's repertoire and possible functional consequences of this phenomenon. Data from human speech research indicates that humans also may unconsciously retain memories of features of languages heard early in life but never spoken.

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Seasonality and overlap between sensory phase and sensorimotor phase in different bird species (Brainard & Doupe, 2002)

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Zebra finches sing the same song all life long, whilst canaries can change it from year-year

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Seasonality and overlap between sensory phase and sensorimotor phase in different bird species (Brainard & Doupe, 2002) research

Bird fanciers have known for centuries that songbirds learn their songs. This learning has striking parallels to speech acquisition: like humans, birds must hear the sounds of adults during a sensitive period, and must hear their own voice while learning to vocalize. With the discovery and investigation of discrete brain structures required for singing, songbirds are now providing insights into neural mechanisms of learning. Aided by a wealth of behavioural observations and species diversity, studies in songbirds are addressing such basic issues in neuroscience as perceptual and sensorimotor learning, developmental regulation of plasticity, and the control and function of adult neurogenesis

13

Zebra finch song development (Bolhuis & Gahr, 2006)

· Until age of 60-80 days - plastic song
- After 100 days - full song

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14

Zebra finch song development (Bolhuis & Gahr, 2006) research

· Song learning in songbirds has strong similarities with speech acquisition in human infants. Songbirds need to learn their songs from an adult conspecific. This occurs in two phases: a memorization phase, early in life, during which the young bird forms a neural representation (a 'template') of the song of a tutor; and a sensorimotor phase, during which the bird's own vocal output is matched to the stored template.
· A network of interconnected brain nuclei, known as the 'song system', is involved in the perception, learning and production of song. Within the song system, the caudal pathway is important for song production. The rostral pathway is involved in song perception and in vocal sensorimotor learning. Initial claims that there are correlations between functional (for example, seasonal or sex) song differences and differences in song system morphology have not been supported by recent findings.
· Two regions outside the song system show neuronal activation (measured as increased expression of immediate early genes) when zebra finches are exposed to song. In one of these regions, the caudomedial nidopallium (NCM), neuronal activation on exposure to the tutor song is significantly correlated with the strength of song learning. An electrophysiological study showed that a familiarity index, based on neuronal habituation rates in the NCM, was significantly greater in tutored males than in untutored males, and significantly positively correlated with the strength of song learning.
· Zebra finch females do not sing, but nevertheless can learn the characteristics of their father's song and form a preference for it over novel songs. When female zebra finches that were reared with their fathers were re-exposed to their fathers' song, they showed significantly greater neuronal activation in the caudomedial mesopallium (CMM), but not in the NCM or hippocampus, compared with when they were exposed to novel song.
· Neuronal activation in the NCM and CMM is not an artefact of isolation rearing, and is not related to attentional mechanisms.
· The NCM and the CMM might be parallel stores that contain the neural substrate for tutor (or father's) song memory, or the 'template'. The NCM might be more directly functionally linked to the premotor nuclei in the song system. The CMM overlaps with the intermediate and medial mesopallium (IMM) that contains the neural substrate for imprinting memory in domestic chicks. The NCM and CMM may be homologous with subdivisions of the mammalian auditory association cortex, which in humans are associated with auditory learning in relation to speech acquisition.
- Further multidisciplinary research is needed to determine whether the NCM and CMM contain the neural substrates of song memory, or whether this information is stored elsewhere in the brain. The neuroanatomical connectivity and functional relationship between these two brain regions and the song system needs to be investigated, in order for us to better understand the overall process of bird song learning. Such analyses may, ultimately, have heuristic value for the study of speech aquisition in humans.

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Birds raised in isolation do not develop full songs (Brainard & Doupe. 2002)

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Birds raised in isolation do not develop full songs (Brainard & Doupe. 2002) research

Feher et al. (2009)

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Brainard and Doupe (2002)

Bird fanciers have known for centuries that songbirds learn their songs. This learning has striking parallels to speech acquisition: like humans, birds must hear the sounds of adults during a sensitive period, and must hear their own voice while learning to vocalize. With the discovery and investigation of discrete brain structures required for singing, songbirds are now providing insights into neural mechanisms of learning. Aided by a wealth of behavioural observations and species diversity, studies in songbirds are addressing such basic issues in neuroscience as perceptual and sensorimotor learning, developmental regulation of plasticity, and the control and function of adult neurogenesis

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Feher et al. (2009)

Culture is typically viewed as consisting of traits inherited epigenetically, through social learning. However, cultural diversity has species-typical constraints1, presumably of genetic origin. A celebrated, if contentious, example is whether a universal grammar constrains syntactic diversity in human languages2. Oscine songbirds exhibit song learning and provide biologically tractable models of culture: members of a species show individual variation in song3 and geographically separated groups have local song dialects4,5. Different species exhibit distinct song cultures6,7, suggestive of genetic constraints8,9. Without such constraints, innovations and copying errors should cause unbounded variation over multiple generations or geographical distance, contrary to observations9. Here we report an experiment designed to determine whether wild-type song culture might emerge over multiple generations in an isolated colony founded by isolates, and, if so, how this might happen and what type of social environment is required10. Zebra finch isolates, unexposed to singing males during development, produce song with characteristics that differ from the wild-type song found in laboratory11 or natural colonies. In tutoring lineages starting from isolate founders, we quantified alterations in song across tutoring generations in two social environments: tutor–pupil pairs in sound-isolated chambers and an isolated semi-natural colony. In both settings, juveniles imitated the isolate tutors but changed certain characteristics of the songs. These alterations accumulated over learning generations. Consequently, songs evolved towards the wild-type in three to four generations. Thus, species-typical song culture can appear de novo. Our study has parallels with language change and evolution12,13,14. In analogy to models in quantitative genetics15,16, we model song culture as a multigenerational phenotype partly encoded genetically in an isolate founding population, influenced by environmental variables and taking multiple generations to emerge

19

Auditory feedback and song templates (Konishi, 1965; Nordeen & Nordeen, 1992)

· Birds deafened (removal of cochlea) prior to onset of subsong stage - no normal song
· Birds match produced song to memorised song template
- Auditory feedback also imp for maintenance of full songs

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20

Auditory feedback and song templates (Konishi, 1965; Nordeen & Nordeen, 1992) research

Nordeen and Nordeen (1992)

21

Nordeen and Nordeen (1992)

Although songbirds rely on auditory input for normal song development, many species eventually attain adult song patterns that are thought to be maintained without reference to auditory feedback. In such species, it is believed that a central motor program for song is established when the stereotyped adult song pattern is achieved. However, we report here that in the Australian zebra finch, stereotyped song patterns gradually change in adult males following bilateral cochlear removal. By 16 weeks after surgery, deaf birds accurately reproduced only 36% of the song syllables produced prior to surgery. Moreover, on average, the phonology of over 50% of the syllables produced by deaf birds was either only slightly similar or unlike the phonology of any syllable produced prior to surgery. In contrast, control birds accurately retained over 90% of their syllables over a comparable time period and less than 5% of their syllables was unmatched or only slightly similar in phonology to previously recorded syllables. In many of the deafened birds, changes in song patterns were not evident until 6–8 weeks after surgery. These data indicate that continued auditory input is necessary to maintain the patterns of neural organization supporting learned song in zebra finches and raise questions concerning the neural sites and cellular mechanisms that mediate this feedback control.

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Developmental plasticity during the sensitive period (Nelson et al., 1995)

· Sensitive period has constrained onset and end time
· But env factors can modulate period:
- Local adaptations in length and onset of breeding season (e.g. coastal v montane populations of white-crowned sparrows)

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- Length and freq of social exposure to singing males (e.g. zebra finches raised by females could learn songs after exposure to males long after end of normally occurring sensitive period; Eales, 1987)

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23

Developmental plasticity during the sensitive period (Nelson et al., 1995) research

Eales (1987)

Bölting and von Engelhardt (2017)

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Eales (1987)

Captive male zebra finches, Taeniopygia guttata, that were raised by females, in complete isolation from adult males, retained the ability to learn song from an adult male when this tutor was later made available to them. Despite their lack of experience of adult males, youngsters recognized the more suitable quality of adult male song, learning it even when they were sexually mature if a tutor became available. They did not use female call notes as song elements unlike those that remained isolated from adult males. The results therefore suggest that, first, young birds do not need to experience adult male song during the dependent period for song learning to occur later and, second, until sufficient suitable material has been heard the sensitive phase remains open-ended, and the young male remains capable of song learning.

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Bölting and von Engelhardt (2017)

▪ Background: Individual differences in behaviour are widespread in the animal kingdom and often influenced by the size or composition of the social group during early development. In many vertebrates the effects of social interactions early in life on adult behaviour are mediated by changes in maturation and physiology. Specifically, increases in androgens and glucocorticoids in response to social stimulation seem to play a prominent role in shaping behaviour during development. In addition to the prenatal and early postnatal phase, adolescence has more recently been identified as an important period during which adult behaviour and physiology are shaped by the social environment, which so far has been studied mostly in mammals. We raised zebra finches (Taeniopygia guttata) under three environmental conditions differing in social complexity during adolescence - juvenile pairs, juvenile groups, and mixed-age groups - and studied males’ behavioural, endocrine, and morphological maturation, and later their adult behaviour.
▪ Results: As expected, group-housed males exhibited higher frequencies of social interactions. Group housing also enhanced song during adolescence, plumage development, and the frequency and intensity of adult courtship and aggression. Some traits, however, were affected more in juvenile groups and others in mixed-age groups. Furthermore, a testosterone peak during late adolescence was suppressed in groups with adults. In contrast, corticosterone concentrations did not differ between rearing environments. Unexpectedly, adult courtship in a test situation was lowest in pair-reared males and aggression depended upon the treatment of the opponent with highest rates shown by group-reared males towards pair-reared males. This contrasts with previous findings, possibly due to differences in photoperiod and the acoustic environment.
- Conclusion: Our results support the idea that effects of the adolescent social environment on adult behaviour in vertebrates are mediated by changes in social interactions affecting behavioural and morphological maturation. We found no evidence that long-lasting differences in behaviour reflect testosterone or corticosterone levels during adolescence, although differences between juvenile and mixed-age groups suggest that testosterone and song behaviour during late adolescence may be associated.

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Social experience influences song development and can override innate predispositions

White-crowned sparrows were exposed to both strawberry finches tutors and own-species song playbacks (Baptista and Petrinovich, 1984)

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Social experience influences song development and can override innate predispositions research

Baptista and Petrinovich (1984)

Ljubicic et al. (2016)

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Baptista and Petrinovich (1984)

Naive 50-day-old white-crowned sparrows (Zonotrichia leucophrys nuttalli) were placed in cages with two compartments in which they could see and interact with a single social tutor. Birds were tutored with the song of their own subspecies, the song of a different subspecies, or that of an alien species, the strawberry finch (Amandava amandava). Each of the 12 birds learned the song of his social tutor. The alien song was learned even though there was abundant conspecific song present in the acoustic environment. These findings indicate that social tutoring can be effective beyond the 10–50-day sensitive phase found with tape tutoring, and that the song of an alien species can be learned from a social tutor. We conclude that neither the sensory template theory nor the current descriptions of the sensitive phase are adequate, without modification, to provide an understanding of song development in the white-crowned sparrow. Because young in the wild learn their songs from social tutors, data from studies of social tutoring provide a better basis to understand factors involved in song learning than data based on studies of tape tutoring

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Ljubicic et al. (2016)

Social animals must learn during development how to integrate successfully into their group. In vocal learners such as songbirds and humans, the development of vocal communication is initially guided by social interactions with the parents. Later on, vocal development is further shaped through interactions with peers and by attending to the consequences of others interacting. It is difficult to assess, however, how social forces combine to shape the outcomes of vocal development. We first review technical advances that make it possible to track social influences on vocal development in songbirds. We then outline methods for simulating the social environment of vocal learning. Such virtual environments would present birds with interactive scenarios in order to directly assess social influences over developmental time scales.

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How do the birds sing?

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