DOI: 10.5061/dryad.tdz08kq3n
title: The effects of ecology and behaviour on the evolution of colouration in Coraciiformes

description: 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 pressures related to behavioural
 characteristics had more spatially localized effects (e.g. territoriality
 on wing feather brightness and hunting strategy on belly hue). Our results
 reveal both general patterns that may hold across other bird clades and
 more nuanced effects of selection that are likely to be mediated through
 the visual ecology of the signaller and receiver and the behavioural
 characteristics of Coraciiform species.
description: 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 analysis.  Second, for each bird
 species that we took colour measurements, we scored the following
 variables: the light of the environment that the particular species
 inhabits (light environment), hunting strategy, body size, the system of
 parental care, and presence and absence of territoriality. The values for
 each variable were scored from the following resources: 1. EltonTraits
 database (Wilman et al., 2014) (Body size); 2. Publications on ecology and
 behavioural traits of Coraciiformes (Fry et al., 1992) (Light environment,
 hunting strategy, parental care, territoriality); 3. Online resources:
 Handbook of the Birds of the world alive (Light environment, parental
 care, territoriality). The information from these resources was processed
 by using already established categories for each of these variables known
 from multiple publications on the ecology and behaviour of
 birds. 
description: Microsoft Excel spreadsheet is necessary to open the data files,
 and R programming language is necessary for further processing.