Carotenoids, Immunocompetence, and the Information Content of Sexual Colors: An Experimental Test

Kevin J. McGraw, Daniel R. Ardia

Research output: Contribution to journalArticlepeer-review

403 Scopus citations


Many male birds use carotenoid pigments to acquire brilliant colors that advertise their health and condition to prospective mates. The direct means by which the most colorful males achieve superior health has been debated, however. One hypothesis, based on studies of carotenoids as antioxidants in humans and other animals, is that carotenoids directly boost the immune system of colorful birds. We studied the relationship between carotenoid pigments, immune function, and sexual coloration in zebra finches (Taeniopygia guttata), a species in which males incorporate carotenoid pigments into their beak to attract mates. We tested the hypotheses that increased dietary carotenoid intake enhances immunocompetence in male zebra finches and that levels of carotenoids circulating in blood, which also determine beak coloration, directly predict the immune response of individuals. We experimentally supplemented captive finches with two common dietary carotenoid pigments (lutein and zeaxanthin) and measured cell-mediated and humoral immunity a month later. Supplemented males showed elevated blood-carotenoid levels, brighter beak coloration, and increased cell-mediated and humoral immune responses than did controls. Cell-mediated responses were predicted directly by changes in beak color and plasma carotenoid concentration of individual birds. These experimental findings suggest that carotenoid-based color signals in birds may directly signal male health via the immunostimulatory action of ingested and circulated carotenoid pigments.

Original languageEnglish (US)
Pages (from-to)704-712
Number of pages9
JournalAmerican Naturalist
Issue number6
StatePublished - Dec 2003
Externally publishedYes


  • Cell-mediated immunity
  • Humoral immunity
  • Ornamental coloration
  • Plasma carotenoids
  • Sexual selection
  • Taeniopygia guttata
  • Zebra finch

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics


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