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Nestling sex ratio in the Southwestern Willow Flycatcher

January 1, 2002

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. 

Publication Year 2002
Title Nestling sex ratio in the Southwestern Willow Flycatcher
DOI 10.1093/condor/104.4.877
Authors E. H. Paxton, M. K. Sogge, T.D. McCarthey, P. Keim
Publication Type Article
Publication Subtype Journal Article
Series Title Condor
Index ID 70024160
Record Source USGS Publications Warehouse
USGS Organization Forest and Rangeland Ecosys Science Center