Least Bell’s Vireo (Vireo bellii pusillus) and Southwestern Willow Flycatcher (Empidonax traillii extimus) Surveys in the Sepulveda Dam Basin, Los Angeles County, California—2022 Data Summary
In 2022, researchers surveyed for Least Bell’s Vireos (Vireo bellii pusillus; vireo) and Southwestern Willow Flycatchers (Empidonax traillii extimus; flycatcher) along Bull Creek, Haskell Creek, and the Los Angeles River within the Sepulveda Dam project area in Los Angeles County, California. Four vireo surveys were conducted between April 26 and July 14, and three flycatcher surveys between May 19 and July 14. A total of 10 territorial male vireos were detected, 5 of which were confirmed as paired, along with 2 transient vireos. Of the territorial vireos, 70 percent were detected along the Los Angeles River, 20 percent along Bull Creek, and 10 percent along Haskell Creek. Most vireos were observed in mixed willow habitat, with 80 percent occurring in areas containing greater than 50 percent native plant cover. One transient flycatcher was also observed in the survey area during 2022.
Pottinger, R.E., and Kus, B.E., 2023, Least Bell’s Vireo (Vireo bellii pusillus) and Southwestern Willow Flycatcher (Empidonax traillii extimus) surveys in the Sepulveda Dam Basin, Los Angeles County, California—2022 data summary: U.S. Geological Survey Data Report 1177, 8 p., https://doi.org/10.3133/dr1177.