Epaulet size and current condition in red-winged blackbirds: Examining a semistatic signal, Testosterone, Immune function, And parasites

Research output: Contribution to journalArticle


Some sexually selected signals are thought to convey information about the current condition and genetic/epigenetic quality of the individual signaling, including the ability to resist parasites. However, it is unclear whether semistatic sexual signals that develop periodically and remain stable over protracted periods, such as avian breeding plumage, can relate to measures of current condition and health. We examined a semistatic signal (wing epaulet size) in male redwinged blackbirds (Agelaius phoeniceus) during the breeding season and looked for relationships between this trait and circulating testosterone (T), hematocrit, bacteriakilling ability (BKA) of the blood, and the infection status, richness, and abundance of four functional categories of parasite. We found that epaulet size was positively related to circulating levels of T and ectoparasite infections. We found no relationships between T and parasite infections. In adult males there was a negative relationship between T and BKA, whereas in yearling males there was no relationship. We found no evidence for a general reduction in immunocompetence in males with larger epaulets but rather an increase in susceptibility to specific types of parasites. Our results suggest that semistatic signals can be linked to measures of current condition, and we postulate that these relationships are modulated via activity levels related to breedingseason activities.


  • Loren Merrill
  • Tara E. Stewart
  • Paulina L. González-Gómez
  • Adrian L.O. O’Loghlen
  • John C Wingfield
  • Vincenzo A. Ellis
  • Stephen I. Rothstein
External organisations
  • University of Illinois at Urbana-Champaign
  • University of California, Santa Barbara
  • University of California, Davis
  • University of Missouri-St. Louis
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Zoology
  • Ecology
Original languageEnglish
Pages (from-to)11-21
Number of pages11
JournalPhysiological and Biochemical Zoology
Issue number1
Publication statusPublished - 2015
Publication categoryResearch
Externally publishedYes