Carotenoid pigments in male house finch plumage in relation to age, subspecies, and ornamental coloration

Auk, The, Oct 2001 by Inouye, Caron Y, Hill, Geoffrey E, Stradi, Riccardo D, Montgomerie, Robert

In this study, we identified and quantified the carotenoids responsible for male House Finch plumage coloration in the subspecies frontalis and griscomi. Our objectives were, first, to elucidate the pigmentary basis for extreme variation in expression of ornamental plumage coloration among males observed within age classes and subspecies. To do that, we investigated how types and amounts of carotenoid pigments in feathers affected both hue (redness) and saturation of plumage coloration among individual males. Alhough we studied males in only two subspecies, a wide range of hues, saturations and patch sizes of ornamental plumage color has been recorded in frontalis and griscomi (Hill 1993a). Second, within both subspecies, we compared carotenoid pigments of hatch-year versus older males to analyze extent to which feather pigmenation was affected by age. Finally, to investigate the proximate basis for differences between subspecies in carotenoid display, we compared their patch sizes and mean hues, total carotenoid abundances, and carotenoid composition of their feathers.

METHODS

DISCUSSION

Pigmentary basis for individual variation in plumage coloration.-For male House Finches of the subspecies C. m. frontalis and C. m. griscomi, the hue of ornamental plumage depended primarily on proportion of red (4-keto-carotenoids) versus yellow pigments deposited in feathers. Relationship between proportion of red pigments and plumage redness was strong and significant for hatch-year and adult frontalis males and for hatch-year griscomi males, but there was no relationship between plumage redness and proportion of red pigments in adult griscomi males. It seems likely that proportion of red pigments was not correlated with plumage redness in adult griscomi males, because there was little detectable variation in hue. That is, all adult males were bright red with a hue of 9 or 10. Lack of variation in plumage hue among adult griscomi males would also explain weak relationships between hue and virtually all component carotenoids (Table 2), the weak negative relationships between plumage redness and concentration of several red pigments, and the weak positive relationships between plumage redness and concentration of several yellow pigments (Table 2).

Contributions of specific carotenoids to variation in plumage hue were different for the various subspecies and age classes of males. 3Hydroxy-echinenone was the most abundant red pigment in the plumage of males from both subspecies and age classes, but its concentration was not always the best predictor of plumage redness. Likewise, lutein was the most abundant yellow pigment in the plumage of both subspecies and age classes that we sampled, but its contribution to plumage redness varied among groups. Total carotenoid concentration in feathers also had a weak but significant effect on plumage hue.

Our observations are similar to those reported for Common (Carduelis flammea) and Hoary (C. hornemanni) redpolls, in which hue differences among individuals were attributed to the concentrations of both lutein (a yellow carotenoid) and echinenone (a red carotenoid) as well as relative concentration of lutein-individuals with higher levels of lutein appeared more orange (Troy and Brush 1983). Similarly, the color polymorphism exhibited by the Sooty-capped Bush Tanager (Chlorospingus pileatus) is due to differing concentrations of lutein in the feathers (Johnson and Brush 1972). 3-Hydroxy-echinenone has also been found to be the primary carotenoid pigment responsible for red plumage color in several other Carpodacus finches, for example, C. roseus and C. rubricilloides (Stradi et al. 1995a, b; 1997), as well as the plumages of Pine Grosbeak (Pinicola eunucleator; Stradi et al. 1996).