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    Sexual dimorphism of song and life history trade-offs in the New Zealand bellbird : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Albany, New Zealand
    (Massey University, 2018) Roper, Michelle Mary
    Birdsong and its function is well studied in terms of male-male competition and female-mate choice. This has generated a male bias in the song literature and the dilemma that little is known about female song. However, recent research posits that female song is not only common but is also the ancestral state of songbirds. Therefore, it is timely that I investigate the ontogeny, structure and production of female song within the context of the life history of female songbirds in order to increase our current understanding of the function and evolution of birdsong. In this thesis, I use a wild population of New Zealand bellbirds (Anthornis melanura) as a model species. The New Zealand bellbird is ideal for this research as they produce complex but sexually dimorphic song. With a cross-sectional approach, I found the songs of each sex diverged and became more consistent as the song developed from juveniles to adults, and that their sexually dimorphic songs developed over similar timeframes, suggesting potentially related functions. I also compared how the adult song repertoire of each sex varied over time, and found that males had larger repertoires at both the population and individual levels. The syllable repertoire of each sex changed at a similar rate due to shifts in relative abundance over time, suggesting both sexes may have analogous song functions and are potentially under similar selection pressures. Sexual variation in song could theoretically be explained by differences in the syrinx structure but there is a lack of comparative research in this field. I found that bellbirds had greater sexual dimorphism in the size of their bronchial half rings compared to species both with and without female song. This suggests syrinx size alone cannot explain sexual dimorphism in repertoire size, but may have a stronger influence on sex- and species-specific song frequencies. Long term studies provide insights to life history and my study population on Tiritiri Matangi Island has breeding data available as far back as 1977. The island’s history of ecological restoration has resulted in exponential growth of the bellbird population, and I found correlated reproductive trade-offs with a reduction in clutch size over time, likely owing to increasing competition for resources. My research demonstrates how female songbirds develop and change their song over time and that they have flexible life-history traits that enable them to cope with changing breeding conditions. My research is significant in that it is one of the first to study female song in a wild population and provides important insights into male and female song development, structure and role.
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    New horizons for female birdsong : evolution, culture and analysis tools : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Auckland, New Zealand
    (Massey University, 2020) Webb, Wesley
    As a result of male-centric, northern-hemisphere-biased sexual selection theory, elaborate female traits in songbirds have been largely overlooked as unusual or non-functional by-products of male evolution. However, recent research has revealed that female song is present in most surveyed songbirds and was in fact the ancestral condition to the clade. Additionally, a high proportion of songbird species have colourful females, and both song and showy colours have demonstrated female-specific functions in a growing number of species. We have much to learn about the evolution and functions of elaborate female traits in general, and female song in particular. This thesis extends the horizons of female birdsong research in three ways: (1) by revealing the broad-scale evolutionary relationship of female song and plumage elaboration across the songbirds, (2) by developing new accessible tools for the measurement and analysis of song complexity, and (3) by showing—through a detailed field study on a large natural metapopulation—how vocal culture operates differentially in males and females. First, to understand the drivers of elaborate female traits, I tested the evolutionary relationship between female song presence and plumage colouration across the songbirds. I found strong support for a positive evolutionary correlation between traits, with female song more prevalent amongst species with elaborated female plumage. These results suggest that contrary to the idea of trade-off between showy traits, female plumage colouration and female song likely evolved together under similar selection pressures and that their respective functions are reinforcing. Second, I introduce new bioacoustics software, Koe, designed to meet the need for detailed classification and analysis of song complexity. The program enables visualisation, segmentation, rapid classification and analysis of song structure. I demonstrate Koe with a case study of New Zealand bellbird Anthornis melanura song, showcasing the capabilities for large-scale bioacoustics research and its application to female song. Third, I conducted one of the first detailed field-based analyses of female song culture, studying an archipelago metapopulation of New Zealand bellbirds. Comparing between male and female sectors of each population, I found equal syllable diversity, largely separate repertoires, and contrasting patterns of sharing between sites—revealing female dialects and pronounced sex differences in cultural evolution. By combining broad-scale evolutionary approaches, novel song analysis tools, and a detailed field study, this thesis demonstrates that female song can be as much an elaborate signal as male song. I describe how future work can build on these findings to expand understanding of elaborate female traits.
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    Influences of environmental and biological factors on song complexity in songbirds : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Auckland, New Zealand
    (Massey University, 2017) Hill, Samuel David
    In songbirds, song is important for mate attraction and territory defence. Females of some species preferentially select males that have more complex songs, an honest signal for male fitness. Examining variation in song complexity provides important insights into the evolution of sexually-selected vocal characteristics. In this thesis, hypotheses examining song complexity variation and a series of biological and environmental factors were tested. A socially monogamous songbird with highly complex songs and high extra-pair paternity (tui, Prosthemadera novaeseelandiae) was selected as the main study model. Firstly, the hypothesis that song complexity in songbird broadcast songs would be higher than in interactive songs was tested. In addition, it was predicted that there would be a positive association between song complexity and extra-pair paternity frequency. This was conducted across 78 songbird species, the most comprehensive analysis in this study area to date. Concordant with the predictions, tui broadcast songs were found to have higher complexity than interactive songs. Furthermore, after controlling for phylogenetic relatedness, a significant positive association between extra-pair paternity frequency and within-song complexity was found across multiple species. Secondly, I tested the hypothesis that tui song complexity would be higher at dawn than at solar noon and dusk. It has previously been established that dawn is a critical period for intensified songbird vocal displays, such as increased song rate. However, little research has been conducted on diurnal variations in song complexity, which was predicted to be higher at dawn. As predicted, both tui song complexity and intrusion rates were significantly greater at dawn than at dusk. In addition, two song complexity variables were inversely correlated with intrusion rate. Thirdly, the hypothesis that male tui would respond more aggressively to more complex songs was tested, to assess whether song complexity plays a role in male-male interactions. Male responses to rival male songs of different degrees of complexity were subsequently examined using playback experiments. Male tui songs with higher complexity evoked stronger and more aggressive intrasexual responses than simple song as predicted. Fourthly, I tested the hypothesis that habitat complexity would correlate positively with tui song complexity. The association between habitat structure and tui song complexity was investigated by comparing male song complexity in two types of habitat: forest remnants with high complexity, and open habitats with lower complexity. As predicted, habitat complexity correlated positively with tui song complexity. Overall, the findings in this thesis provide evidence that several biological and environmental factors are associated with the evolution of song complexity; a socially-selected vocal trait. This study suggests that complex songs in vocally complex songbirds may have evolved under extra-pair paternity, territorial and environmental pressures. It therefore has implications for furthering our understanding of song complexity evolution in songbirds.
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    Wavelet-based birdsong recognition for conservation : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Computer Science at Massey University, Palmerston North, New Zealand
    (Massey University, 2017) Priyadarshani, Nirosha
    According to the International Union for the Conservation of Nature Red Data List nearly a quarter of the world's bird species are either threatened or at risk of extinction. To be able to protect endangered species, we need accurate survey methods that reliably estimate numbers and hence population trends. Acoustic monitoring is the most commonly-used method to survey birds, particularly cryptic and nocturnal species, not least because it is non-invasive, unbiased, and relatively time-effective. Unfortunately, the resulting data still have to be analysed manually. The current practice, manual spectrogram reading, is tedious, prone to bias due to observer variations, and not reproducible. While there is a large literature on automatic recognition of targeted recordings of small numbers of species, automatic analysis of long field recordings has not been well studied to date. This thesis considers this problem in detail, presenting experiments demonstrating the true efficacy of recorders in natural environments under different conditions, and then working to reduce the noise present in the recording, as well as to segment and recognise a range of New Zealand native bird species. The primary issues with field recordings are that the birds are at variable distances from the recorder, that the recordings are corrupted by many different forms of noise, that the environment affects the quality of the recorded sound, and that birdsong is often relatively rare within a recording. Thus, methods of dealing with faint calls, denoising, and effective segmentation are all needed before individual species can be recognised reliably. Experiments presented in this thesis demonstrate clearly the effects of distance and environment on recorded calls. Some of these results are unsurprising, for example an inverse square relationship with distance is largely true. Perhaps more surprising is that the height from which a call is transmitted has a signifcant effect on the recorded sound. Statistical analyses of the experiments, which demonstrate many significant environmental and sound factors, are presented. Regardless of these factors, the recordings have noise present, and removing this noise is helpful for reliable recognition. A method for denoising based on the wavelet packet decomposition is presented and demonstrated to significantly improve the quality of recordings. Following this, wavelets were also used to implement a call detection algorithm that identifies regions of the recording with calls from a target bird species. This algorithm is validated using four New Zealand native species namely Australasian bittern (Botaurus poiciloptilus), brown kiwi (Apteryx mantelli ), morepork (Ninox novaeseelandiae), and kakapo (Strigops habroptilus), but could be used for any species. The results demonstrate high recall rates and tolerate false positives when compared to human experts.
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    Effects of urban noise on vocalisations of tūī (Prosthemadera novaeseelandiae) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Conservation Biology at Massey University, Auckland, New Zealand
    (Massey University, 2015) Ludbrook, Miriam Robin
    The two most important functions of avian acoustic communication are territory defence and mate attraction. As such the effective communication of these signals is critical for individual reproductive success. However if these vocal signals are masked by anthropogenic noise, their signal efficiency is reduced and this may result in direct negative fitness consequences. Therefore knowledge on how urban habitat features including anthropogenic noise affect avian vocal communication is important in understanding the evolution of animal communications in urban ecosystems. Such knowledge is also important for the management of endangered and declining species in urban areas. Little is known about how birds respond to the highly variable levels of urban noise in urban habitats. In this study I investigated spectral and temporal differences in songs between populations of tūī (Prosthemadera novaeseelandiae) in urban habitats with both high noise levels (near motorway) and lower noise levels (distant from motorway). Male long-range tūī songs were collected during the breeding season (October 2012 to February 2013) at three paired sites, with one of each pair situated within 100m of a motorway and the matching site within 2-3 kilometres from the first site and the motorway. Urban noise levels (dB) were measured at all sites. I compared motorway and non-motorway urban songs to determine whether tūī shift the frequency, duration, trill components and output of songs in response to anthropogenic noise. Songs were also recorded at two paired non-urban sites over 50 kilometres from the urban sites (Mahurangi Regional Park and Wenderholm Regional Park) and spectral characteristics were also compared between these non-urban and the urban sites. I compared song rate and singing rate to investigate whether song output varied with noise levels and between urban and non-urban habitats. Through comparison of the degree of syllable sharing and proportion of unique syllables and phrases at these sites, I explored the presence of song dialects at urban and non-urban sites. From 63.5 hours of field sampling, I collected a total of 1017 long-range broadcast songs (627 songs from motorway sites and 390 songs from nonmotorway sites). A significantly higher minimum frequency was found in songs III from the noisier, motorway sites compared with those from non-motorway sites. Motorway songs had shorter song durations and decreased syllable diversity than non-motorway songs. There were also a significantly lower proportion of trills in the songs at sites near to motorway. As predicted a smaller syllable repertoire size was found in the sites near the motorway compared to repertoires at nonmotorway sites. The presence of site-specific syllables and phrases and site-specific clusters in a Ward cluster analysis, as well as a reduced degree of syllable sharing between urban sites indicated the formation of local dialects in these fragmented urban sites. This study has provided data of bird song variation within urban ecosystems of varying noise levels. These findings aid our understanding of modifications to tūī songs to avoid the masking effects of low frequency traffic noise. Song duration, trill proportion and repertoire size have all been demonstrated as being subject to sexual selection. Changes in these aspects at noisy urban sites are considered adaptations to urban effects. Such changes may have further implications for other important behavioural aspects such as mate choice and can have profound effects on tūī population dynamics between urban fragments. Understanding these urban effects on bird songs and other important behavioural aspects are important not only for advances in ecological theory in urban ecology, but also for conservation management of urban habitats. For example, dialects between urban fragments may create a reproductive barrier for dispersing birds, therefore reducing gene flow between sites. Habitat corridors should be considered in urban designs, not only to increase gene flow of species with poor dispersal ability, but may also help to connect populations of highly mobile species such as tūī.