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
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Date
2019
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Massey University
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Abstract
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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Keywords
European blackbird, Color, Behavior, Carotenoids, Passeriformes, Sexual dimorphism (Animals)