The feathers of birds harbor a diverse assemblage of microorganisms. Some of these microorganisms have the capability to break down keratin, the primary constituent of feathers. I addressed two questions in my research. 1) Does the deposition of pigments in feathers influence the rate at which bacteria can degrade feathers? 2) Do feather-degrading bacteria influence the expression of feather coloration? With respect to question (1), I found that melanin pigments inhibit bacterial degradation of feathers. With respect to question (2), I found evidence that feather-degrading bacteria can influence structural feather color expression (through the dulling of feathers), but that this effect may be sex dependent. Furthermore, I found a sex-dependent correlation between the number of bacteria on a bird and body condition, consistent with feather-degrading bacteria having an effect on the mass of birds.
Gunderson, A.R., A.M. Frame, J.P. Swaddle, and M.H. Forsyth. 2008. Resistance of melanized feather to bacterial degradation: is it really so black and white? Journal of Avian Biology. 39: 539-545. (pdf)
Gunderson, A.R. 2008. Feather-degrading bacteria: a new frontier in avian and host-parasite research? Auk. 125(4): 972-979. (pdf)
Gunderson, A.R., M.H. Forsyth, and J.P. Swaddle. 2009. Evidence that plumage bacteria influence feather coloration and body condition of eastern bluebirds Sialia sialis. Journal of Avian Biology 40: 440-447. (pdf)