Age before beauty? Relationships between fertilization success and age-dependent ornaments in barn swallows

Jan T. Lifjeld, Oddmund Kleven, Frode Jacobsen, Kevin McGraw, Rebecca J. Safran, Raleigh J. Robertson

Research output: Contribution to journalArticlepeer-review

35 Scopus citations


When males become more ornamented and reproduce more successfully as they grow older, phenotypic correlations between ornament exaggeration and reproductive success can be confounded with age effects in cross-sectional studies, and thus say relatively little about sexual selection on these traits. This is exemplified here in a correlative study of male fertilization success in a large colony of American barn swallows (Hirundo rustica erythrogaster). Previous studies of this species have indicated that two sexually dimorphic traits, tail length and ventral plumage coloration, are positively correlated with male fertilization success, and a mechanism of sexual selection by female choice has been invoked. However, these studies did not control for potential age-related variation in trait expression. Here, we show that male fertilization success was positively correlated with male tail length but not with plumage coloration. We also show that 1-year-old males had shorter tails and lower fertilization success than older males. This age effect accounted for much of the covariance between tail length and fertilization success. Still, there was a positive relationship between tail length and fertilization success among older males. But as this group consisted of males from different age classes, an age effect may be hidden in this relationship as well. Our data also revealed a longitudinal increase in both tail length and fertilization success for individual males. We argue that age-dependent ornament expression and reproductive performance in males complicate inferences about female preferences and sexual selection.

Original languageEnglish (US)
Pages (from-to)1687-1697
Number of pages11
JournalBehavioral Ecology and Sociobiology
Issue number9
StatePublished - Sep 2011


  • Extrapair paternity
  • Hirundo rustica
  • Life-history variation
  • Plumage coloration
  • Sexual selection
  • Tail length

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Animal Science and Zoology


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