Distribution of unique red feather pigments in parrots

Abstract

In many birds, red, orange and yellow feathers are coloured by carotenoid pigments, but parrots are an exception. For over a century, biochemists have known that parrots use an unusual set of pigments to produce their rainbow of plumage colours, but their biochemical identity has remained elusive until recently. Here, we use high-performance liquid chromatography to survey the pigments present in the red feathers of 44 species of parrots representing each of the three psittaciform families. We found that all species used the same suite of five polyenal lipochromes (or psittacofulvins) to colour their plumage red, indicating that this unique system of pigmentation is remarkably conserved evolutionarily in parrots. Species with redder feathers had higher concentrations of psittacofulvins in their plumage, but neither feather colouration nor historical relatedness predicted the ratios in which the different pigments appeared. These polyenes were absent from blood at the time when birds were replacing their colourful feathers, suggesting that parrots do not acquire red plumage pigments from the diet, but instead manufacture them endogenously at growing feathers.

Figure 1

Representative three-dimensional HPLC chromatograms from one species in each of the three parrot families: (a) male African grey parrot (Psittacus erithacus, Psittacidae), (b) male red lory (Eos bornea, Loriidae) and (c) male red-tailed black cockatoo (Calyptorhynchus banksii, Cacatuidae). Note the presence of the same set of five psittacofulvins in each: (i) unidentified pigment, t_R=6.4 min, λ_max=438 nm; (ii) eicosanonenal, t_R=6.7 min, λ_max=438 nm; (iii) octadecaoctenal, t_R=7.9 min, λ_max=424 nm; (iv) hexadecaheptenal, t_R=9.6 min, λ_max=443 nm; (v) tetradecahexenal, t_R=15.8 min, λ_max=443 nm. The z-axis is truncated at 375 nm in all panels because these pigments showed no absorbance peaks in the UV.

Figure 2

Psittacofulvin composition of red feathers from parrots found in each of the three main parrot families. Standard errors are shown above each bar, which denotes the species means (n=number of species) for each pigment type within a family. In separate two-way analyses of variance for the five psittacofulvins, we found no effect of sex (all p>0.07), family (all p>0.15), or sex-by-family interaction (all p>0.35) on the percentage () of total pigments that each comprised. We did, however, find that there was a significant effect of sex (F_1,39=4.0, p=0.04) and family (F_2,39=7.4, p=0.02) on ()total feather-pigment concentration (no sex-by-family interaction; p>0.3). Post hoc tests revealed that male feathers contained more pigments than females (Fisher's PLSD, p=0.01) and that lory feathers contained more than feathers of psittacids and cockatoos (Fisher's PLSD, both p<0.02; p=0.25 for pairwise comparison between psittacids and cockatoos). (c) Representative UV–VIS reflectance spectra for the red feathers of the three species for which HPLC chromatograms are shown in figure 1. See Siefferman & Hill (2003) for these spectrophotometric methods.