Vocal performance in the chipping sparrow: can a bird change his song?

Bird song is an animal signal that serves as the primary method of mate attraction in most songbirds, a group that accounts for the majority of bird species worldwide. While it has been established that there can be a wide range in song quality within a species, and that high-quality vocal performance tends to attract more mates, less is known about the effects of differing vocal performance on the behavior of other competing males. It also has not been established whether individual birds can alter their own vocal performance quality in response to different situations. In some birds that sing a trilled vocalization, it is possible to quantitatively define the vocal skill required to produce a given song. In this Honors Thesis, I explore these issues in the chipping sparrow (Spizella passerina), whose trilled vocalization facilitates measurement of the vocal skill required to produce a given song. I tested three competing hypotheses concerning the vocal performance of this species: (1) that individuals modulate their song quality in different competitive contexts, (2) that individuals differ from one another in their vocal performance and are unable to modulate their vocal performance, and (3) that individuals are neither different from one another nor modulate their vocal performance. Over the course of a single breeding season, chipping sparrows were captured, color-banded, and recorded as they sang spontaneously. In a playback experiment simulating territorial intrusions by both high- and low-quality males, tested birds did not modulate any aspect of their vocal performance outside of singing more often while a simulated intruder was also singing (p=0.223). In all contexts, the largest source of variation in song was attributable to inherent differences between individuals (

Social Influences on Songbird Behavior: From Song Learning to Motion Coordination

Social animals learn during development how to integrate successfully into their group. How do social interactions combine to maintain group cohesion? We first review how social environments can influence the development of vocal learners, such as songbirds and humans (Chapter 1). To bypass the complexity of natural social interactions and gain experimental control, we developed Virtual Social Environments, surrounding the bird with videos of manipulated playbacks. This way we were able to design sensory and social scenarios and test how social zebra finches adjust their behavior (Chapters 2 & 3). A serious challenge is that the color output of a video monitor does not match the color vision of zebra finches. To minimize chromatic distortion, we eliminated all of the colors from the videos, except in the beak and cheeks where we superimposed colors that match the sensitivity of zebra finch photoreceptors (Chapter 2). Birds strongly preferred to watch these manipulated ‘bird appropriate’ videos. We also designed Virtual Social Environments for assessing how observing movement patterns might affect behavior in real-time (Chapter 3). We found that presenting birds with manipulated movement patterns of virtual males promptly affects the mobility of birds watching the videos: birds move more when virtual males increase their movements, and they decrease their movements and ‘cuddle’ next to virtual males that stop moving. These results suggest that individuals adjust their activity levels to the statistical patterns of observed conspecific movements, which can explain zebra finch group cohesion. Finally, we studied the song development process in the absence of social input to determine how intrinsic biases and external stimuli shape song from undifferentiated syllables into well-defined categorical signals of adult song (Chapter 4). Do juveniles learn the statistics of early sub-song to guide vocal development? We trained juvenile zebra finches with playbacks of their own, highly variable, developing song and showed that these self-tutored birds developed distinct syllable types (categories) as fast as birds that were trained with a categorical, adult song template. Therefore, the statistical structure of early input seems to have no bearing on the development of phonetic categories. Overall, our results uncover social forces that influence individual behaviors, from motion coordination to vocal development, which have implications for how group structures and vocal culture are maintained

Immanuel Kant's Sparrow

The adoption of foreign song elements occurs under natural conditions in various songbird species including the house sparrow Passer domesticus, even though it may go largely unnoticed by humans. House sparrows singing canary song have been known by hobbyists for a long time. My study is the first to analyse the imitative abilities of house sparrows in detail. I used an integrative approach considering features that are particularly important for the degree of vocal learning that can be displayed by a species. These included (1) a genetic predisposition, (2) body condition of the parents, (3) food availability during early ontogeny, (4) social factors, (5) neuronal mechanisms, (6) hormonal states, and (7) body size and morphology of the vocal tract. House sparrows singing canary-like songs provide a rich tool for further integrative approaches. I suggest an interpretation combining all the above features under the perspective of female choice. Instead of searching for a „key adaptation“ or single explanation for the imitative ability (song learning ability) in passerines, it might be more appropriate to focus on the multiplicity of factors involved in song production that - shaped by different selective forces - promote the highly specific song adaptations.Schon seit Jahrhunderten sind Haussperlinge bei Vogelliebhabern als gelehrige Imitatoren fremder Laute und Gesänge bekannt. Am häufigsten wird von Sperlingen berichtet, die von Kanarienvögeln aufgezogen wurden und den Kanariengesang lernten. Wissenschaftlern hingegen blieb dieses Wissen bislang weitgehend verborgen. In dieser Arbeit wird erstmals der wissenschaftliche Nachweis erbracht, dass Sperlinge tatsächlich den Kanariengesang lernen und produzieren. Dazu habe ich einen integrativen Forschungsansatz verwendet, der folgende Aspekte umfasst (1) Einflüsse der Aufzucht durch Kanarienvögel oder Sperlinge; (2) Gesänge von Haussperlingen, aufgezogen von Kanarienvögeln oder Sperlingen; (3) Gehirnstrukturen (HVc, RA), welche dem Gesang zugrunde liegen; (4) Einflüsse von Steroidhormonen (Testosteron, DHEA) auf die Gesangsproduktion; (5) Einflüsse des Stimmapparates auf die Gesangsproduktion. Summa summarum zeigt diese Arbeit, dass eine Verhaltensweise wie ‚Singen’ auf dem komplexen Zusammenspiel vieler verschiedener Faktoren beruht, von denen keiner vernachlässigt werden darf: (a) Der ‚kanarisch’ singende Hausperling offenbart sich als ideales Subjekt für einen integrativen Forschungsansatz, der - mindestens - Neurobiologie, Endokrinologie, Verhaltensbiologie, funktionale Morphologie, und Life History verbindet; (b) Beim Vergleichen des Gesang von verschiedenen Vogelarten sollte zukünftig nicht nur auf phylogenetische Nähe bzw. Ferne korrigiert werden, sondern auch auf die unterschiedliche Körpergröße; (c) Gesang sollte folglich nicht mehr nur als eine einheitliche Anpassung betrachten werden, sondern als hoch spezialisiertes Ergebnis vieler verschiedener, in Wechselwirkung stehender Anpassungen, geformt unter unterschiedlichen Selektionsdrücken

Seeing sound: a new way to illustrate auditory objects and their neural correlates

This thesis develops a new method for time-frequency signal processing and examines the relevance of the new representation in studies of neural coding in songbirds. The method groups together associated regions of the time-frequency plane into objects defined by time-frequency contours. By combining information about structurally stable contour shapes over multiple time-scales and angles, a signal decomposition is produced that distributes resolution adaptively. As a result, distinct signal components are represented in their own most parsimonious forms.  Next, through neural recordings in singing birds, it was found that activity in song premotor cortex is significantly correlated with the objects defined by this new representation of sound. In this process, an automated way of finding sub-syllable acoustic transitions in birdsongs was first developed, and then increased spiking probability was found at the boundaries of these acoustic transitions. Finally, a new approach to study auditory cortical sequence processing more generally is proposed. In this approach, songbirds were trained to discriminate Morse-code-like sequences of clicks, and the neural correlates of this behavior were examined in primary and secondary auditory cortex. It was found that a distinct transformation of auditory responses to the sequences of clicks exists as information transferred from primary to secondary auditory areas. Neurons in secondary auditory areas respond asynchronously and selectively -- in a manner that depends on the temporal context of the click. This transformation from a temporal to a spatial representation of sound provides a possible basis for the songbird's natural ability to discriminate complex temporal sequences

Assessing the Phylogenetic and Cultural Content of Learned Song

In the oscine songbirds, song is learned by a juvenile from a tutor of the same species, in a pattern that is analogous to human language, and likewise has the potential to change over time by cultural evolution. The similarities between human languages have been studied for centuries, but historically the relationships between the songs of birds of different species have been seen as too divergent to be useful. Using a computational analysis of song databases coupled with genetic phylogenies, I have shown that there is indeed a significant correlation between genetic distance and song similarity in the oscines. For a subset of Emberizid species, it was possible to reconstruct a genus-level phylogeny using the song syntax of these birds. For one member of this subset, I traced the cultural evolution of song properties, both over time and across distances. In addition, I examined the role of innate predispositions in song learning by hybridizing two species of Estrildid finches and examining the vocal output of hybrids in comparison with normally raised and cross-fostered birds. This work represents the first large-scale evolutionary analysis of learned song and the first clear demonstration of the relationship between genetic relatedness and song similarity

Stabilizing Forces in Acoustic Cultural Evolution: Comparing Humans and Birds

Learned acoustic communication systems, like birdsong and spoken human language, can be described from two seemingly contradictory perspectives. On one hand, learned acoustic communication systems can be remarkably consistent. Substantive and descriptive generalizations can be made which hold for a majority of populations within a species. On the other hand, learned acoustic communication systems are often highly variable. The degree of variation is often so great that few, if any, substantive generalizations hold for all populations in a species. Within my dissertation, I explore the interplay of variation and uniformity in three vocal learning species: budgerigars (Melopsittacus undulatus), house finches (Haemorhous mexicanus), and humans (Homo sapiens). Budgerigars are well-known for their versatile mimicry skills, house finch song organization is uniform across populations, and human language has been described as the prime example of variability by some while others see only subtle variations of largely uniform system. For each of these species, I address several questions related to variability and uniformity: What is the typical range of variation? What are the limits of variation? How are those two issues related? And what mechanisms underlie variability and uniformity? In chapter 3, I investigate a potential domain of uniformity in budgerigar warble: the segment. Segments, units divided by acoustic transitions rather than silence, have been largely ignored in non-human animal communication. I find that budgerigars can achieve a high degree of complexity and variability by combining and arranging these small, more stereotyped units. Furthermore, I find that budgerigar segment organization is not only consistent across independent budgerigar populations but is consistent with patterns found in human language. In chapter 4, I investigate variability in house finch song. I present data showing that house finches learn sound patterns which are absent in wild house finch populations. These data suggest that cross-population variation in house finch song is narrower than what is permitted by the house finch song learning program. Finally, in chapter 5, I focus on human language, the most well-described communication system. Here, I research a sound pattern that is absent in the majority of known languages. I find that the rare pattern has independently developed at least six times. In every case, the historical pathway which led to the rare pattern was the same. The historical development in these six linguistic lineages suggests that the overall rarity of the sound pattern is the result of acoustic similarity. These data illuminate the evolutionary forces that give rise to, and limit, variation. The results of this dissertation have wide-ranging implications, from necessary revisions of linguistic theories, to understanding epigenetic interactions, to the application of evolutionary theory to complex behavior. While these projects within the dissertation are all different, evidence from all three projects support the following claims: (i) cross-population commonality is not evidence for what a species is able to learn; (ii) peripheral mechanisms have a strong influence in limiting cross-population variability; and (iii) high degrees of variation can emerge from uniform traits