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

Executive 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 Bull Creek, Haskell Creek, and the Los Angeles River (Sepulveda Dam project area) in Los Angeles County, California, in 2018. Four vireo surveys were conducted between April 27 and July 18, 2018, and three flycatcher surveys were conducted between May 24 and July 18, 2018. We found 14 territorial male vireos, 7 of which were confirmed as paired. Sixty-four percent of vireos were detected along the Los Angeles River, 21 percent along Haskell Creek, and 14 percent along Bull Creek. Eighty-six percent of vireos were detected in habitat characterized as mixed willow, and all vireos were detected in habitat with greater than 50 percent native plant cover. No flycatchers were observed in the survey area in 2018.