Body size and climate as predictors of plumage colouration and sexual dichromatism in parrots

Abstract

Psittaciformes (parrots, cockatoos and lorikeets) comprise one of the most colourful clades of birds. Their unique pigments and safe cavity nesting habits are two potential explanations for their colourful character. However, plumage colour varies substantially between parrot species and sometimes also between males and females of the same species. Here, we use comparative analyses to evaluate what factors correlate with colour elaboration, colour diversity and sexual dichromatism. Specifically, we test the association between different aspects of parrot colouration and (a) the intensity of sexual selection and social interactions, (b) variation along the slow‐fast life‐history continuum and (c) climatic variation. We show that larger species and species that live in warm environments display more elaborated colours, yet smaller species have higher levels of sexual dichromatism. Larger parrots tend to have darker and more blue and red colours. Parrots that live in wetter environments are darker and redder, whereas species inhabiting warm regions have more blue plumage colours. In general, each of the variables we considered explain small to moderate amounts of variation in parrot colouration (up to 15%). Our data suggest that sexual selection may be acting more strongly on males in small, short‐lived parrots leading to sexual dichromatism. More elaborate colouration in both males and females of the larger, long‐lived species with slow tropical life histories suggests that mutual mate choice, social selection and reduced selection for crypsis may be important in these species, as has been shown for passerines.

Body size and sexual selection shaped the evolution of parrot calls

“…We used data on body size, habitat type, gregariousness and colour ornamentation from Carballo et al (2020), which comprise data for 230 of the 252 species in our acoustic traits dataset. Briefly, as a measure of body size, we took the first Principal Component (PC) of a standard Principal Component Analysis (PCA) on wing, tarsus and tail lengths (both male and female), which explains 87.2% of variation in the original size measurements (trait loadings: 0.97 for male and also for female wing length, 0.94 for male and also for female tarsus length and 0.87 for male tail length 0.89 for female tail length).…”

“…We quantified colour ornamentation based on the six colour variables computed by Carballo et al (2020) from analyses of digital colour plates of parrot species in the HBW; these were: a colour elaboration score for males and another for females (based on the difference between the plumage colours of a species and the average colours across all parrot species), a colour diversity score for males and another for females (based on the diversity or uniformity of all plumage colours in a species), plus two measures of sexual dichromatism, one the male minus female colour elaboration score and the other the male minus female colour diversity score. We ran a PCA to reduce collinearity in these colour variables and used the first two PCs, which together explained 67.7% of the initial variation (Table 1).…”

“…We did not include body mass in this PCA because data on mass is missing for many species. For the subset of species with body mass in Carballo et al (2020), this first PC correlates strongly with body mass (simple Pearson correlation, r = 0.87, N = 187 spp.). For habitat type, species were scored as either open-habitat species (score 0; e.g.…”

United colours of the city: A review about urbanisation impact on animal colours

“…The tropics have the most colourful birds (Carballo et al . 2020), and therefore, the impact of urbanisation on plumage colour composition and diversity may be stronger than in temperate regions. Moreover, interspecific studies are much scarcer than intraspecific ones.…”

Sexual dimorphism in immune function and oxidative physiology across birds: The role of sexual selection

“…To quantify sexual dichromatism, plumage colouration was measured in both sexes following the methodology described in Dale et al ( 2015 ) and Carballo et al ( 2020 ) (see Supplementary Methods for details). The mating system was scored based on information obtained from birdsoftheworld.org, Snow et al ( 1998 ) and other studies (Liker et al, 2015 ; Olson et al, 2008 ).…”