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Distribution and Abundance of Least Bell’s Vireos (Vireo bellii pusillus) and Southwestern Willow Flycatchers (Empidonax traillii extimus) at the Mojave River Dam, San Bernardino County, California—2024 Data Summary

Open-File Report 2025-1025
Ecosystems Mission Area—Species Management Research Program
By:  and 
https://doi.org/10.3133/ofr20251025

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Abstract

We surveyed for Least Bell’s Vireos (Vireo bellii pusillus; vireo) and Southwestern Willow Flycatchers (Empidonax traillii extimus; flycatcher) at the Mojave River Dam study area near Hesperia, California, in 2024. Four vireo surveys were completed between April 17 and July 2, 2024, and three flycatcher surveys were completed between May 23 and July 2, 2024.

We detected three territorial male vireos, all of which were paired. No juveniles were observed during surveys. Vireo territories were reported in two habitat types: riparian scrub and willow-cottonwood. Red or arroyo willow (Salix laevigata or lasiolepis) was the dominant plant species in most vireo territories. No territorial or transient flycatchers were observed.

Suggested Citation

Howell, S.L., and Kus, B.E., 2025, Distribution and abundance of Least Bell’s Vireos (Vireo bellii pusillus) and Southwestern Willow Flycatchers (Empidonax traillii extimus) at the Mojave River Dam, San Bernardino County, California—2024 data summary: U.S. Geological Survey Open-File Report 2025–1025, 8 p., https://doi.org/10.3133/ofr20251025.

ISSN: 2331-1258 (online)

Study Area

Table of Contents

  • Acknowledgments
  • Executive Summary
  • Introduction
  • Methods
  • Results
  • Summary
  • References Cited
Publication type Report
Publication Subtype USGS Numbered Series
Title Distribution and abundance of Least Bell’s Vireos (Vireo bellii pusillus) and Southwestern Willow Flycatchers (Empidonax traillii extimus) at the Mojave River Dam, San Bernardino County, California—2024 data summary
Series title Open-File Report
Series number 2025-1025
DOI 10.3133/ofr20251025
Publication Date May 13, 2025
Year Published 2025
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Western Ecological Research Center
Description vi, 8 p.
Country United States
State California
County San Bernardino County
Other Geospatial Mojave River Dam
Online Only (Y/N) Y
Additional publication details