Technical Report

2024 Southwestern Willow Flycatcher Survey Results – Belen Reach, Middle Rio Grande, New Mexico

URL: https://webapps.usgs.gov/mrgescp/documents/2024-Belen-Reach-SWFL_Report_Final_TetraTech.pdf

Date: 2025/02/19

Author(s): Grbic J., Sanderson C.

Publication: Prepared by RJH Consultants Inc., Englewood, CO and Tetra Tech Inc., Albuquerque, NM for Bureau of Reclamation, Albuquerque Area Office, NM.

Abstract:

In 2024 the Bureau of Reclamation (Reclamation) retained RJH Consultants, Inc. (RJH) and Tetra Tech, Inc. (Tetra Tech) to conduct presence/absence surveys and nest monitoring for the Federally listed endangered Southwestern Willow Flycatcher (Empidonax trailli extimus), or SWFL, within a 6,280-acre study area in the Belen Reach along approximately 30 river miles of the Middle Rio Grande (MRG). This study was designed to inform overall management of the Belen Reach and to support Endangered Species Act (ESA) compliance needs for Reclamation, the Middle Rio Grande Conservancy District, and the New Mexico Interstate Stream Commission. Additionally, survey activities within the Belen Reach contribute to the overall understanding of SWFL distribution within the MRG, population trends, and baseline population data.

Due to potential impacts along the MRG from water management, river infrastructure restoration and maintenance, and conservation work outlined in the MRG Biological Opinion (2016), ”project-related surveys” (as outlined in the survey protocol by Sogge et al., 2010) were completed in the Belen Reach. SWFL surveys were conducted five times between May 15 and July 23. Tetra Tech biologists field activities comprised a total of 344.6 observer-hours on SWFL protocol-level surveys in which 182 resident SWFLs were documented, representing 96 territories and 86 pairs. The Belen Reach supported 96 territories in 2024, representing a 1.1 percent increase from 95 territories in 2022.

SWFL nest monitoring was completed between June 24 and August 12, 2024. The nest monitoring program assessed nesting success rates, productivity, depredation, abandonment, and Brown-headed Cowbird (Molothrus ater) parasitism. A total of 57 SWFL nests were found and 43 fledged young were documented in the Belen Reach, which resulted in overall nesting success rate of 43%. Nest success dropped by 9 percent in 2024 compared to 2022 results.