Least Bell’s Vireo (Vireo bellii pusillus) and Southwestern Willow Flycatcher (Empidonax traillii extimus) surveys in the Hansen Dam Basin, Los Angeles County, California—2018 data summary

We surveyed for Least Bell’s Vireos (Vireo bellii pusillus; vireo) and Southwestern Willow Flycatchers (Empidonax traillii extimus; flycatcher) in cooperation with the U.S. Army Corps of Engineers along Big Tujunga Creek in the Hansen Dam Basin in Los Angeles County, California, in 2018. Four vireo surveys were conducted between April 25 and July 17, 2018, and three flycatcher surveys were conducted between May 22 and July 17, 2018. We found 77 territorial male vireos, 54 of which were confirmed as paired. Seventy-seven percent of vireos were detected in habitat characterized as mixed willow, and 84 percent of vireos were detected in habitat with greater than 50 percent native plant cover. One transient Willow Flycatcher of unknown subspecies was observed in the survey area in 2018.