Song learning in domesticated canaries in a restricted acoustic environment

Involvement of the neural social behaviour network during social information acquisition in zebra finches (Taeniopygia guttata)

Female zebra finches Taeniopygia guttata will copy the novel foraging choice of males. The degree to which they do so, however, can vary considerably. Among-individual differences in social learning and their underlying neural pathways have received relatively little attention and remain poorly understood. Here, then, we allowed female zebra finches to observe live-streamed male demonstrators feeding from one of two novel-coloured feeders (social information acquisition phase). After this social information acquisition phase, we tested from which feeder the females preferred to feed to determine whether they copied the feeder choice of the male demonstrator (social learning test phase). We then examined the brains of these females for immediate early gene activity (c-fos) in the neural social behaviour network for the time during which they were observing the male feeding. Of the 12 regions and sub-regions in the brain examined we found only one weak correlation: greater copying was associated with lower activity in the bed nucleus of the stria terminalis, BSTmv. Future work should perhaps focus on neural activity that occurs during the stage in which there is evidence that animals have copied a demonstrator (i.e., social learning test phase in the current experiment) rather than during the period in which those animals observe that demonstrator (i.e., social information acquisition phase in the current experiment). What is clear is that the considerable emphasis on examining the behavioural component of social learning has not yet been accompanied by neural analyses.

Evidence for cumulative cultural evolution in bird song

In studies of cumulative cultural evolution in non-human animals, the focus is most often on incremental changes that increase the efficacy of an existing form of socially learned behaviour, such as the refinement of migratory pathways. In this paper, we compare the songs of different species to describe patterns of evolution in the acoustic structure of bird songs, and explore the question of what building blocks might underlie cumulative cultural evolution of bird song using a comparative approach. We suggest that three steps occurred: first, imitation of independent sounds, or notes, via social learning; second, the formation of categories of note types; and third, assembling note types into sequences with defined structures. Simple sequences can then be repeated to form simple songs or concatenated with other sequences to form segmented songs, increasing complexity. Variant forms of both the notes and the sequencing rules may then arise due to copy errors and innovation. Some variants may become established in the population because of learning biases or selection, increasing signal efficiency, or because of cultural drift. Cumulative cultural evolution of bird songs thus arises from cognitive processes such as vocal imitation, categorization during memorization and learning biases applied to basic acoustic building blocks. This article is part of a discussion meeting issue 'The emergence of collective knowledge and cumulative culture in animals, humans and machines'.

Accelerated redevelopment of vocal skills is preceded by lasting reorganization of the song motor circuitry

Complex motor skills take considerable time and practice to learn. Without continued practice the level of skill performance quickly degrades, posing a problem for the timely utilization of skilled motor behaviors. Here we quantified the recurring development of vocal motor skills and the accompanying changes in synaptic connectivity in the brain of a songbird, while manipulating skill performance by consecutively administrating and withdrawing testosterone. We demonstrate that a songbird with prior singing experience can significantly accelerate the re-acquisition of vocal performance. We further demonstrate that an increase in vocal performance is accompanied by a pronounced synaptic pruning in the forebrain vocal motor area HVC, a reduction that is not reversed when birds stop singing. These results provide evidence that lasting synaptic changes in the motor circuitry are associated with the savings of motor skills, enabling a rapid recovery of motor performance under environmental time constraints.

Genetic variation interacts with experience to determine interindividual differences in learned song

Learning reflects the influence of experience on genetically determined circuitry, but little is known about how experience and genetics interact to determine complex learned phenotypes. Here, we used vocal learning in songbirds to study how experience and genetics contribute to interindividual differences in learned song. Previous work has established that such differences in song within a species depend on learning, but in principle some of these differences could also depend on genetic variation. We focused on song tempo, a learned and quantifiable feature that is controlled by central neural circuitry. To identify genetic contributions to tempo we computer-tutored juvenile Bengalese finches (Lonchura striata domestica) from different genetic backgrounds with synthetic songs in which tempo was systematically varied. Computer-tutored birds exhibited unexpectedly strong heritability for song tempo and comparatively weak influence of experience. We then tested whether heritability was fixed and independent of experience by providing a second group of birds with enriched instruction via live social tutoring. Live tutoring resulted in not only a significant increase in the influence of experience on tempo but also a dramatic decrease in the influence of genetics, indicating that enriched instruction could overcome genetic biases evident under computer tutoring. Our results reveal strong heritable genetic contributions to interindividual variation in song tempo but that the degree of heritability depends profoundly on the quality of instruction. They suggest that for more complex learned phenotypes, where it can be difficult to identify and control relevant experiential variables, heritability may similarly be contingent on the specifics of experience.

Domestication changes innate constraints for birdsong learning

Birdsongs are acquired by imitating the sounds produced by conspecifics. Within a species, songs diverge by cultural transmission, but the range of species-specific features is restricted by innate constraints. Bengalese finches (Lonchura striata var. domestica) are a domesticated strain of the wild White-rumped munia (Lonchura striata). The songs of the domesticated strain have more tonal sounds and more variable sequences than those of the wild strain. We compared the features of songs that were produced by normal birds, isolation-reared birds, and cross-fostered birds in both White-rumped munias and Bengalese finches to identify differences in the genetic and environmental factors of their songs. Factor analyses were conducted based on 17 song measurements. We found that isolated songs differed from normal and cross-fostered songs, especially in unstable prosodic features. In addition, there were significant differences in sound property of mean frequency between the two strains regardless of the rearing conditions. Thus, innate constraints that partially determine birdsong phenotypes may be altered through domestication.

Quantitative integration of genetic factors in the learning and production of canary song

Learned bird song is influenced by inherited predispositions. The canary is a model system for the interaction of genes and learning on behaviour, especially because some strains have undergone artificial selection for song. In this study, roller canaries (bred for low-pitched songs) and border canaries (whose song is higher pitched, similar to the wild-type) were interbred and backcrossed to produce 58 males that sorted into seven genetically distinct groups. All males were tutored with the same set of songs, which included both low- and high-pitched syllables. Individuals were consistent within genetic groups but differed between groups in the proportion of low- versus high-pitched syllables they learned and sang. Both sex-linked and autosomal factors affected song learning and song production, in an additive manner. Dominant Z-chromosome factors facilitated high-pitched syllable learning and production, whereas the sex-linked alleles associated with the switch to low-pitched syllables under artificial selection were largely recessive. With respect to autosomal effects, the most surprising result is that males in the same genetic group had almost identical repertoires. This result challenges two common preconceptions: that genetic changes at different loci lead to distinct phenotypic changes, and that genetic predispositions affect learning in simple and general ways. Rather, different combinations of genetic changes can be associated with the same phenotypic effect; and predispositions can be remarkably specific, such as a tendency to learn and sing one song element rather than another.

Long-range order in canary song

Bird songs range in form from the simple notes of a Chipping Sparrow to the rich performance of the nightingale. Non-adjacent correlations can be found in the syntax of some birdsongs, indicating that the choice of what to sing next is determined not only by the current syllable, but also by previous syllables sung. Here we examine the song of the domesticated canary, a complex singer whose song consists of syllables, grouped into phrases that are arranged in flexible sequences. Phrases are defined by a fundamental time-scale that is independent of the underlying syllable duration. We show that the ordering of phrases is governed by long-range rules: the choice of what phrase to sing next in a given context depends on the history of the song, and for some syllables, highly specific rules produce correlations in song over timescales of up to ten seconds. The neural basis of these long-range correlations may provide insight into how complex behaviors are assembled from more elementary, stereotyped modules.

Bird songs range in form from the simple notes of a Chipping Sparrow to the complex repertoire of the nightingale. Recent studies suggest that bird songs may contain non-adjacent dependencies where the choice of what to sing next depends on the history of what has already been produced. However, the complexity of these rules has not been examined statistically for the most elaborate avian singers. Here we show that one complex singer—the domesticated canary—produces a song that is strongly influenced by long-range rules. The choice of how long to repeat a given note or which note to choose next depends on the history of the song, and these dependencies span intervals of time much longer than previously assumed for birdsong. Like most forms of human music, the songs of canaries contain patterns expressed over long timescales, governed by rules that apply to multiple levels of a temporal hierarchy. This vocal complexity provides a valuable model to examine how ordered behaviors are assembled from more elementary neural components in a relatively simple neural circuit.