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
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Date
2017
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Massey University
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Abstract
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.
Description
Content removed for copyright reasons: Hill, S. D., Pawley, M. D. M., Anderson, M. G., & Weihong, J. (2017). Higher song complexity and intruder pressure at dawn in a vocally complex songbird. Emu - Austral Ornithology, 118(2), 147-157. doi:10.1080/01584197.2017.1380503
Keywords
Birdsongs, Birds, Behaviour, Tūi, New Zealand