The effect of coccidial infection on iridescent plumage coloration in wild turkeys

Wild turkeys, Meleagris gallopavo, are among the most ornamented birds in North America, displaying vividly coloured fleshy ornaments on their heads and bright, iridescent structural coloration in their plumage. We investigated the effect of experimental inoculation with coccidian parasites on the expression of iridescent structural coloration in yearling male turkeys. Prior to moult of ornamental feathers, we assigned turkeys to three experimental groups: we maintained six turkeys free of coccidial infection, inoculated four turkeys with a single species of coccidial oocysts, and inoculated six turkeys with multiple species of coccidial oocysts. We used reflectance spectrometry to quantify the plumage coloration of wing covert and breast feathers in the breeding plumage of males in each treatment protocol. We found significant treatment-based variation in the iridescent plumage coloration of yearling male turkeys such that infected males showed proportionately less UV reflectance in their wing covert and breast feathers and had duller breast feathers. This is the first experimental evidence that parasites can suppress the expression of structural plumage coloration, and our findings suggest that, in wild turkeys, iridescent coloration could serve as a condition-dependent signal of male health.