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    Investigating patterns of avian ornamental colouration : intraspecific and interspecific approaches : a thesis presented in partial fulfilment of the requirements for the degree of Masters of Science in Zoology at Massey University, Albany, New Zealand
    (Massey University, 2019) Ahlstrom, Millie Beatrice May
    Research into the evolutionary function of elaborated colouration in birds is continually ongoing. Novel approaches to addressing various aspects of this broad research area may help us consider this topic in a new light. This thesis aimed to consider two different aspects of avian colouration research using novel methods and testing relatively new hypotheses. Firstly, I consider the cost of carotenoid pigmented ornamental colouration - an area of research that is currently under intense debate. Classically carotenoid-based pigmentation has considered carotenoids to function as indicators of sexual quality, with costs being due to carotenoids being diet dependent in birds. Recent research however has argued that carotenoid pigmented colour traits function in agonistic social contexts, and that the cost of using carotenoid pigmentation as an honest indicator of quality is a social one. In this study I test this hypothesis using blackbirds (Turdus merula) and their natural variation in carotenoid-based bill colouration. I replicate a study using model presentations to simulate territory intrusions. Additionally, I examine the feasibility of using three-dimensionally printed models in avian behavioural studies. This study was unsuccessful due to a lack of response rates from territorial males, however it was successful in questioning several differing aspects between my study and the study I replicated. Secondly, I explore the spatial organisation of colouration on the bodies of birds as a way of potentially inferring different functions of elaborate colour traits. In the third chapter I develop a novel method that allows objective analysis of the spatial organisation of colour on the bodies of birds, by removing morphological variation between species. Using this method I present a case study on the spatial organisation of colour elaboration in 2,471 species of passerines. This case study uses a difference in sexual dichromatism as a proxy for colour elaboration and determined where signaling hotspots occur on the bodies of birds. These results demonstrate that conspicuous colouration is most common in the supercilium, chin, and upper breast of passerine birds. In chapter four, I used this method to determine correlations between different life-history traits and different regions of the body. This study aimed to infer the function of different regions of the head in signaling. My results show that the irises in species with tropical life-histories and cooperative breeding strategies are more likely to be elaborately coloured; bills of larger bodied species are more likely to be elaborately coloured than are smaller species; and the spatial organisation of colour effects females more than it does males.
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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.