The effects of ecology and behaviour on the evolution of colouration in Coraciiformes

What drives the evolution of plumage colour in birds? Bird colour is likely to be under both natural and sexual selection where natural selection may favour evolution towards crypsis or camouflage whereas sexual selection may favour evolution towards conspicuousness. The responses to selection are predicted to relate to species’ ecology, behaviour, and life history. Key hypotheses have focused on habitat and light environment, breeding strategy, territoriality, and hunting behaviour. We tested these potential causes of colour variation in the Coraciiformes, a colourful clade of non-passerine birds, using phylogenetic comparative methods and data on plumage colouration and brightness measured from museum specimens. We found that correlates of colour evolution in Coraciiformes vary across body regions and depend on the focal colour property (hue or brightness). While light environment showed widespread effects on colouration in multiple body regions for both hue and brightness, selection ..., Two sets of data were collected for this research.
First, in the Natural History Museum at Tring bird collection, we used bird skins of 135 Coraciiformes species to measure plumage colouration. Calibrated digital images of study skins were taken using methods described in Cooney et al. (2019). They were used to quantify both chromatic (hue and saturation) and achromatic (brightness) components of the colour. We draw a series of polygons on every image representing body patches. We covered 11 body patches on each specimen. We extracted RGB values from each polygon and then converted them to avian colourspace values (cone catch values: u, s, m, and l). These values represent the chromatic measurement of bird colour. We also extracted an achromatic measurement of colour as the stimulation value of double cones. Following, we have used Principal component analysis to reduce the dimensionality of cone catch values from 4 (i.e. u, s, m, l) to 2 values (PC1 and PC2) that we used for further an..., Microsoft Excel spreadsheet is necessary to open the data files, and R programming language is necessary for further processing.Â