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
Loading...
Date
2018
DOI
Open Access Location
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Massey University
Rights
The Author
Abstract
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.
Description
Appendix B: Reprint of Published Paper was removed for copyright reasons.
Keywords
Korimako, Birdsongs, New Zealand, Sexual dimorphism (Animals), Birds, Vocalization