Date of Award


Publication Type

Doctoral Thesis

Degree Name



Biological Sciences


colour, evolution, plumage, tetrachromatic


Stephanie M Doucet




In this dissertation, I investigated the function and evolution of plumage-based visual signals in trogons (Trogoniformes), and assessed the influence of individual parameters in the receptor-noise model of colour discriminability. In Chapter 2, I investigated the function of tail raising in the elegant trogon. For this purpose, I used observational and experimental data collected in Costa Rica. Results demonstrated that tail raising in the elegant trogon is a multifunctional signal that targets both conspecifics and heterospecifics. Specifically, trogons used this behaviour during intra and intersexual interactions, and the experiment confirmed that tail raising is a pursuit-deterrent signal. In Chapter 3, I experimentally tested which plumage patches are used in species recognition in two species of trogons: the black-headed trogon, which is sympatric with a similar-looking congener, and the elegant trogon, which is not sympatric with a similar-looking congener. The results suggested that while both species use the back and belly colour as specie- recognition traits, the black-headed trogon but not the elegant trogon also assessed the tail banding pattern. In Chapter 4, I investigated the relationship between sympatry and plumage divergence in the genus Trogon. My results demonstrated that Trogon taxa diversified more rapidly, and that plumage trait divergence increased with sympatric overlap in South American but not Central American taxa. Together, my findings suggested that the rapid colonization of South America following the Great American Interchange resulted in reinforcement through character displacement or trait sorting. In Chapter 5, I investigated how dichromatism scores are influenced by individual parameters of the receptor-noise model of chromatic contrast threshold, using an avian-based tetrachromatic approach. I systematically tested parameter values for ambient light environment, photoreceptor sensitivities and densities, transmission properties of the ocular media and oil droplets, and compared the sensory experience of species for which the visual system has been fully characterized. My results demonstrated that oil droplet characteristics, photoreceptor densities, and the sensitivity of the SWS1 photoreceptor (ultraviolet sensitive or not) had the most influence on dichromatism scores. I encourage the complete characterization of visual systems when possible, and my results will inform researchers when making inferences about tetrachromatic visual models.