Captive Rearing Experiments Confirm Song Development without Learning in a Tracheophone Suboscine Bird

The origin of vocal learning in animals has long been the subject of debate, but progress has been limited by uncertainty regarding the distribution of learning mechanisms across the tree of life, even for model systems such as birdsong. In particular, the importance of learning is well known in oscine songbirds, but disputed in suboscines. Members of this diverse group (∼1150 species) are generally assumed not to learn their songs, but empirical evidence is scarce, with previous studies restricted to the bronchophone (non-tracheophone) clade. Here, we conduct the first experimental study of song development in a tracheophone suboscine bird by rearing spotted antbird (Hylophylax naevioides) chicks in soundproofed aviaries. Individuals were raised either in silence with no tutor or exposed to standardized playback of a heterospecific tutor. All individuals surviving to maturity took a minimum of 79 days to produce a crystallized version of adult song, which in all cases was indistinguishable from wild song types of their own species. These first insights into song development in tracheophone suboscines suggest that adult songs are innate rather than learnt. Given that empirical evidence for song learning in suboscines is restricted to polygamous and lek-mating species, whereas tracheophone suboscines are mainly monogamous with long-term social bonds, our results are consistent with the view that sexual selection promotes song learning in birds

Dialect formation in fragmented populations of the endangered North Island kokako (Callaeas wilsoni)

The role of behavioural ecology in the conservation of species and biodiversity remains poorly understood. Observational and experimental studies of bird song, using a biogeographic approach, provide an opportunity to address this issue. Here I test hypotheses on the emergence and divergence of song cultures related to historical as well as more recent population fragmentation events. The North Island kōkako (Callaeas wilsoni) is a duetting songbird endemic to New Zealand that was once widespread but, due to habitat loss and introduced predators, has become endangered. These birds are sedentary and monogamous with poor flying abilities. Therefore, all of the c. 1500 surviving individuals are marooned in 13 scattered surviving populations and 11 translocated populations. The historical fragmentation of populations, the kōkako’s territorial nature and capacity to learn songs, and the establishment of new populations through translocation make this species a good candidate for studies on the emergence of song cultures, social divergence and landscape effects on conservation from a behavioural perspective. Song sharing and comparisons of acoustic characteristics were used to reconstruct associations of song traditions and acoustic traits at both macrogeographic and microgeographic levels in the six largest surviving populations of kōkako (Chapter 2 and 3). Distinct song cultures or dialects were discovered in all populations examined. However, patterns of vocal similarity observed were not correlated with historical fragmentation patterns or linear geographical distance (Chapter 2). Instead, rapid vocal drift following fragmentation and isolation as well as founder effects linked to population contraction may explain current macrogeographic song variation (Chapter 3). Nevertheless, a fragmentation effect on song similarity, generating song repertoire divergence, was observed at a microgeographic scale within discontinuous populations (Chapter 2). In addition, juvenile dispersal across portions of tenuously connected habitat, which have strikingly different song cultures, suggests that kōkako learn songs after dispersal (Chapter 2). Post-dispersal learning may explain the lack of consistency between dialect membership and genetic relatedness among surviving populations. Dialect formation may occur as different cultural trajectories are forged by fragmentation and isolation; subsequent song convergence may then occur due to social selection or chance events. The effects of population size on song attributes, repertoires and sharing, vocal versatility and syntactical structure were examined within the six largest natural populations, as well as two translocated populations of kōkako (Chapter 3). Repertoire size, song diversity and the predictability of syntactical structure were positively correlated with population size. Song traditions and the rate of cultural evolution may depend on social interaction and population size, as the neutral model of song microevolution predicts. Smaller populations of kōkako, with reduced social stability under relaxed selection pressures, may resemble small colonizing groups undergoing founder effects and vocal drift leading to loose syntax, consistent with the ‘withdrawal of learning’ hypothesis. Furthermore, social modulation of vocal behaviour and song traditions are discussed in the context of reproductive success and adaptation to differing social conditions as in the case of translocation events (Chapter 3). Recently isolated translocated populations exhibit remarkable acoustic divergence and reduced song sharing with the corresponding source population (Chapter 4). Translocated populations showed relatively low song diversity and increased song sharing as well as acoustically distinct song features. To investigate how meaningful this vocal divergence was for individuals in source and translocated populations, a reciprocal playback experiment was performed to examine vocal and approach responses to simulated local and non-local intruders. Responses to simulated intruders differed among populations but there was little evidence of discrimination based on stimulus type. The degree of song divergence (i.e., repertoire and acoustic features) and vocal response to playback relative to the source population was greater in an older translocated population than a more recently translocated population (Chapter 4). Consistent with the consequences of founder effects and vocal drift, these results demonstrate that kōkako populations vocally diverge in isolation following the establishment of a population with a vocal subset and subsequently a different cultural trajectory (in accordance with the ‘withdrawal of learning’ hypothesis). Cultural erosion in small translocated populations may affect their viability as reduced vocal virtuosity can be associated with a reduced capacity for territory defense and mate attraction, and consequently low reproductive success. Song divergence can ultimately have important implications for our understanding of the evolution of animal societies and our ability to conserve animal populations

Acoustics of anthropogenic habitats: The impact of noise pollution on eastern bluebirds

An increasing number of habitats are affected by anthropogenic noise pollution, which is often louder, has a different frequency emphasis, and may occur over a different temporal scale, than natural noise. An increasing number of studies indicate that acoustically-communicating animals in such areas can modify their vocalizations in order to make themselves heard over the noise, but many questions still remain, including: How taxonomically widespread is vocal flexibility in response to anthropogenic noise, and do all vocally flexible species employ the same mechanisms to escape acoustic masking? Are there fitness repercussions for living, communicating, and breeding in noisy habitats? and, can particular habitat features be used to predict environmental noise levels and sound propagation characteristics? Here, I present data collected from the breeding territories of eastern bluebirds (Sialia sialis ) to address each of these questions. My results add another species to the list of those who are able to avoid acoustic masking by modifying temporal and spectral traits of vocalizations. I also show that anthropogenic noise is associated with changes in several eastern bluebird breeding parameters. Finally, I demonstrate that both anthropogenic noise levels and sound propagation traits can be predicted by particular habitat characteristics

ECOLOGY OF MATING PATTERNS AND SEXUAL SELECTION IN DICKCISSELS BREEDING IN MANAGED PRAIRIE

Males of many species have elaborate phenotypes that are absent in females and that are thought to be the result of sexual selection. Sexual selection requires: (i) variance in male mating success, (ii) variation in male phenotype, and (iii) covariation between male mating success and male phenotype. Environmental conditions influence these factors, and management practices that alter environmental conditions have the potential to shape mating patterns and sexual selection. I investigated the hypothesis that the frequency of fire, used to manage tallgrass prairie, affects the mating patterns and process of sexual selection in the organisms breeding in managed prairies. I studied dickcissels (Spiza americana), a small songbird resident in tallgrass prairie. I first examined mating patterns and sexual selection in dickcissels independent of burning regime. I found variation among males in the number of mates attracted, in the number of offspring sired with each mate, and the offspring sired with the mates of other males. I found a positive association between social mates and siring success, but no evidence for an effect of breeding density or synchronous nesting on mating success. Male dimorphic traits, size, song, and plumage, showed between-individual variation but selection gradients were weak and often fluctuated between the years of study. I next examined patterns of mating success in plots burned on a variable schedule. I found little evidence that burning influenced either the mean or the variance in social mating success, paternity, or male phenotype. Burning regime also had no influence on sexual selection gradients with the single exception of selection on tarsus length. Temporal variation was more important for patterns of mating success and sexual selection gradients on male traits than was burning regime. The demography of dickcissels in the breeding season suggests, however, that habitat management on a larger scale may be more influential. My findings extend our understanding of sexual selection in birds and the effects of management on the factors required for sexual selection and the magnitude of selection

Sex role similarity and sexual selection predict male and female song elaboration and dimorphism in fairy-wrens

Historically, bird song complexity was thought to evolve primarily through sexual selection on males; yet, in many species, both sexes sing and selection pressure on both sexes may be broader. Previous research suggests competition for mates and resources during short, synchronous breeding seasons leads to more elaborate male songs at high, temperate latitudes. Furthermore, we expect male–female song structure and elaboration to be more similar at lower, tropical latitudes, where longer breeding seasons and year-round territoriality yield similar social selection pressures in both sexes. However, studies seldom take both types of selective pressures and sexes into account. We examined song in both sexes in 15 populations of nine-fairy- wren species (Maluridae), a Southern Hemisphere clade with female song. We compared song elaboration (in both sexes) and sexual song dimorphism to latitude and life-history variables tied to sexual and social selection pressures and sex roles. Our results suggest that song elaboration evolved in part due to sexual competition in males: male songs were longer than female songs in populations with low male survival and less male provisioning. Also, female songs evolved independently of male songs: female songs were slower paced than male songs, although only in less synchronously breeding populations. We also found male and female songs were more similar when parental care was more equal and when male survival was high, which provides strong evidence that sex role similarity correlates with male–female song similarity. Contrary to Northern Hemisphere latitudinal patterns, male and female songs were more similar at higher, temperate latitudes. These results suggest that selection on song can be sex specific, with male song elaboration favored in contexts with stronger sexual selection. At the same time, selection pressures associated with sex role similarity appear to favor sex role similarity in song structure

Dialects in animals: Evidence, development and potential functions

International audienceDialects are one of the parallels that have long been established between human language and animal communication. We discuss the potential functional parallels between human and animal dialects, arguing that in both cases different mechanisms and functions may be at stake where large geographical versus very localized (e.g. social) variations are concerned. Birdsong studies in particular, but also recent studies of mammal vocalizations, show that the use of the term “dialect” to refer to within-species vocal variations in animal species is more than a metaphor and that animal dialects offer a possibility to explore the causes and functions of linguistic variation and change, one of the challenges in exploring the origin of diversity of language families. We present here an original view, as our approach was not "primate-centered" and take into consideration “homoplasy” (analogy) as a potential mechanism to explain that different taxa have evolved the same functional response to social constraints

Explaining geographic variation in the elaborate vocal display of the male Albert’s lyrebird Menura alberti

In this thesis I investigate geographic variation in the song of the Albert’s lyrebird (Menura alberti). The Albert’s lyrebird is a large, Near Threatened, oscine passerine found in a restricted area of subtropical eastern Australia. Male lyrebirds are known for their extended bouts of vocal mimicry that form part of an elaborate multimodal display, but males also produce their own, species-specific vocalisations. Albert’s lyrebirds have experienced substantial habitat loss since European settlement, and are highly sedentary, restricting cultural transmission between geographically distant populations and allowing for considerable variation in vocalisations across the range. Geographic variation in both species-specific song and mimetic song has been anecdotally reported, but never formally quantified. The Albert’s lyrebird’s complex, variable vocalisations make it an ideal model species to investigate geographic variation in a range of vocalisations (described in Chapter 2). Furthermore, as Albert’s lyrebirds are a threatened species, it is important to document existing behavioural variation. Such variation may then be used to identify potential targets for conservation. Overall, I found that male Albert’s lyrebirds exhibit significant geographic variation in multiple vocalisation types and at several levels of song organisation. These patterns of geographic variation highlight the complexity of geographic variation in vocalisations. I also demonstrate how geographic variation can provide insights into other aspects of vocal behaviours. Through variation in mimetic repertoire size, composition, and organisation, I provide evidence that mimicry is at least partially learnt from conspecifics, in line with previous research suggesting that mimicry is learnt from both conspecifics and heterospecifics. The high acoustic contrast between consecutive units within the sequences of all populations suggests that repertoire complexity is an important feature of the vocal mimicry. I highlight the need to investigate temporal organisation of mimetic repertoires in other mimicking species in order to understand the function of mimicry across multiple taxa. Finally, I demonstrate the impact of anthropogenic habitat change on the cultural diversity of Albert’s lyrebirds, and suggest that mimetic diversity may provide an indicator of population health. This thesis adds to the growing body of literature on the impacts of anthropogenic disturbance on vocal diversity, and how vocal cultures may be useful in conservation management

Song perception in communication networks

Communication is a cornerstone of animal behavior and mediates myriad interactions pertaining to survival and reproduction. For animals that communicate acoustically, signals are carried to multiple receivers in what is described as communication networks. In my dissertation, I explore how songbirds and their songs are perceived and used in networks. First, I examine a dilemma many animals face when communicating in a network – how do animals contend with overlapping, conspecific noise? Using a playback experiment in the field, I document Black-capped Chickadees (Poecile atricapillus) shifting the frequency of their song in the presence of overlapping noise. Next, I examine song function in communication networks, and evidence for social eavesdropping. Using Chipping Sparrows (Spizella passerina), I first explored what song parameters territorial males find salient. I found residents are attentive to variation in trill rate or how quickly notes are repeated per unit time. In a parallel experiment, I found no evidence that males attended to a related song parameter – the total frequency range covered in a song, although I did find evidence these two parameters trade-off. In further work, I found males are attentive to the song performance of their neighbors, and occasionally cooperate to help expel intruders. My work reveals that males cooperate under specific circumstances; when the resident under attack has a relatively slow song, and the simulated intruder has a comparatively fast song. These field studies suggest neighbor-turned-allies are most likely to help nearby residents when the intruder is relatively threatening, and suggests males may eavesdrop on their neighbors. Finally, I surveyed Chipping Sparrow neighborhoods throughout Western Massachusetts and was unable to detect any effect of social factors on territory choice. Together, my work describes some disadvantages and advantages songbirds face in communicating in networks, and contributes to our understanding of the importance of networks in signal evolution

The avian dawn chorus across Great Britain: using new technology to study breeding bird song

The avian dawn chorus is a period of high song output performed daily around sunrise during the breeding season. Singing at dawn is of such significance to birds that they remain motivated to do so amid the noise of numerous others. Yet, we still do not fully understand why the dawn chorus exists. Technological advances in recording equipment, data storage and sound analysis tools now enable collection and scrutiny of large acoustic datasets, encouraging research on sound-producing organisms and promoting ‘the soundscape’ as an indicator of ecosystem health. Using an unrivalled dataset of dawn chorus recordings collected during this thesis, I explore the chorus throughout Great Britain with the prospect of furthering our understanding and appreciation of this daily event. I first evaluate the performance of four automated signal recognition tools (‘recognisers’) when identifying the singing events of target species during the dawn chorus, and devise a new ensemble approach that improves detection of singing events significantly over each of the recognisers in isolation. I then examine daily variation in the timing and peak of the chorus across the country in response to minimum overnight temperature. I conclude that cooler temperatures result in later chorus onset and peak the following dawn, but that the magnitude of this effect is greater at higher latitude sites with cooler and less variable overnight temperature regimes. Next, I present evidence of competition for acoustic space during the dawn chorus between migratory and resident species possessing similar song traits, and infer that this may lead either to fine-scale temporal partitioning of song, such that each competitor maintains optimal output, or to one competitor yielding. Finally, I investigate day-to-day attenuation of song during the leaf-out period from budburst through to full-leaf in woodland trees, and establish the potential for climate-driven advances in leaf-out phenology to attenuate song if seasonal singing activity in birds has not advanced to the same degree. I find that gradual attenuation of sound through the leaf-out process is dependent on the height of the receiver, and surmise that current advances in leaf-out phenology are unlikely to have undue effect on song propagation. This project illustrates the advantage of applying new technology to ecological studies of complex acoustic environments, and highlights areas in need of improvement, which is essential if we are to comprehend and preserve our natural soundscapes