Carotenoid-based bill colour as an indicator of immunocompetence and sperm performance in male mallards

A. Peters, A. G. Denk, K. Delhey, B. Kempenaers

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124 Citations (Scopus)


Female mate choice is often based on exaggerated sexual traits, signals of male qualities that females cannot assess directly. Two such key qualities are male immune and/or sexual competence, whereby honesty in signalling could be maintained by physiological trade-offs. Carotenoid-based ornaments likely constitute such honest signals, as there is direct competition for (limited) carotenoids between ornament deposition and anti-oxidant support of immune or sperm functioning. Using spectrometry, we assessed the potential signalling function of the yellow, carotenoid-based colour of the bill of male mallards, a target of female mate choice. Here we demonstrate that bill reflectance varied with plasma carotenoid level, indicating antioxidant reserves. Moreover, lower relative UV reflectance during autumn pairing predicted immune responsiveness and correlated positively with sperm velocity during breeding, a trait that affects fertility. Our data provide support for current theories that females could use carotenoid-based sexual signals to detect immune vigour and fertilizing ability of prospective mates.

Original languageEnglish
Pages (from-to)1111-1120
Number of pages10
JournalJournal of Evolutionary Biology
Issue number5
Publication statusPublished - Sep 2004
Externally publishedYes


  • Antibody production
  • Carotenoids
  • Immunocompetence handicap
  • Indicator
  • Ornament colour
  • Phenotype-linked fertility
  • Sexual selection
  • Spectrometry
  • Sperm velocity
  • SRBC

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