Nestling sex ratio in the Southwestern Willow Flycatcher

Eben H. Paxton, Mark K. Sogge, Tracy D. McCarthey, Paul Keim

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


Using molecular-genetic techniques, we determined the gender of 202 Southwestern Willow Flycatcher (Empidonax traillii extimus) nestlings from 95 nests sampled over a five-year period. Overall nestling sex ratio did not vary significantly from 50:50 among years, by clutch order, or by mating strategy (monogamous vs. polygamous pairings). However, we did observe significant differences among the four sites sampled, with sex ratios biased either toward males or females at the different sites. Given the small population sizes and geographic isolation of many of the endangered subspecies' breeding populations, sex-ratio differences may have localized negative impacts.

Original languageEnglish (US)
Pages (from-to)877-881
Number of pages5
Issue number4
StatePublished - Nov 2002


  • Empidonax traillii
  • Endangered species
  • Nestling sex ratio
  • Willow Flycatcher

ASJC Scopus subject areas

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


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