A project undertaken at Massey University, and supervised by Michelle Roper.
Songbirds are most known for their melodious song, but songbird vocalisations can range from simple, repetitive sounds through to the complex and melodious song we are familiar with. This makes songbirds excellent interdisciplinary models for understanding the evolution of complex vocalisations. However, birdsong evolutionary theory has focussed on males, discounting the important (and potentially different) mechanisms under which female song has evolved. To better understand how complex vocalisations evolved, we also need to understand the mechanisms of song production.
Song is produced via the avian vocal organ, the syrinx, and sex differences in the size of the syrinx structures link with two measures of vocal complexity – repertoire size and fundamental frequency. However, with this only being studied in two species, broader comparisons across avian clades is necessary to ask the question: what is the relative importance of sex differences in syrinx morphology on the production of complex vocalizations? We predict that syrinx structure has played an important role in the evolution of complex vocalizations, but the relative importance of these structures is needed to be understood in a broader context of the ecology and life-history traits of species. Hence, we also ask how has vocal complexity across sexes and species evolved as a result of three factors: morphology, ecology and life-history traits?
The supporting elements (ossified cartilage) of the songbird syrinx.
Three examples of honeyeater vocalisations: a) call of a bell miner (Manorina melanophrys), b) song of a male singing honeyeater (Gavicalis virescens), and c) song of a female korimako (Anthornis melanura).
To answer these questions, we will study the honeyeater (Meliphagidae) family; a large songbird family present across Australia, New Zealand and the Pacific. This family is one of the earliest groups of songbirds to have evolved and the species have a diverse range of morphological, ecological and life-history traits. Honeyeaters also vary in the presence and complexity of female song across species, making this an ideal group to test how vocal diversity and morphological structures are linked.
Using three-dimensional images of honeyeater syrinxes, we will examine what aspects of the vocal organ in both sexes contribute to the production of complex vocalisations. Furthermore, we will test what the effects of morphological, ecological and life-history traits have been on the evolution of vocal complexity. This will give us unbiased insights into how complex animal vocalisations evolve.
This project brings together an international team of researchers from New Zealand (Massey University), Australia (University of New England, Australian National University) and beyond (such as the Okinawa Institute of Science and Technology). These researchers combine their passion and expertise in bioacoustics, behavioural ecology and evolutionary theory to understand how and why birds produce a wide range of vocalisations. This project will also contribute to our knowledge on how our local Australasian fauna has evolved in this unique landscape of the Australasian-Pacific region.