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A high incidence of brown-headed cowbird parasitism of willow flycatchers

February 1, 1988

Brown-headed Cowbirds (Molothrus ater) parasitize both Willow (Empidonax traillii) and Alder (E. alnorum) flycatchers (Friedmann et al. 1977, Friedmann and Kiff 1985). These two flycatchers were considered a single species until 1973 (AOU 1973), which has masked information about the frequency with which each is parasitized. Whereas several studies of the superspecies (Traill's Flycatcher) have focused on or included details of cowbird parasitism, most were of eastern populations, and most reported frequencies of parasitism ≤21% (Hicks 1934, Berger 1951, Berger and Parmalee 1952, Walkinshaw 1966, Holcomb 1972). Friedmann et al. (1977:13) suggested that western populations (Willow Flycatchers) are parasitized only about half as much (ca. 10%) as eastern populations (Traill's Flycatcher superspecies). This note described a high rate of cowbird parasitism within a population of Willow Flycatchers in northcentral Colorado. We include details of responses to parasitism and host vs. cowbird fledgling success.

Publication Year 1988
Title A high incidence of brown-headed cowbird parasitism of willow flycatchers
DOI 10.2307/1368461
Authors James A. Sedgwick, Fritz L. Knopf
Publication Type Article
Publication Subtype Journal Article
Series Title The Condor
Index ID 70122140
Record Source USGS Publications Warehouse