Technical Report

2005 Southwestern Willow Flycatcher Study Results

URL: https://webapps.usgs.gov/mrgescp/documents/Reclamation_2006_2005SWFLReport.pdf

Date: 2006/03/01

Author(s): Reclamation

Publication: U.S. Bureau of Reclamation Report, 47 p.

Abstract:

During the summer of 2005, the Bureau of Reclamation (Reclamation) conducted surveys and nest monitoring of the federally endangered Southwestern Willow Flycatcher (Empidonax traillii extimus) (SWFL) in eight distinct reaches along approximately 165 kilometers of the Middle Rio Grande adjacent to Velarde, New Mexico, and between the Pueblo of Isleta and Elephant Butte Reservoir. Surveys were performed to contribute to current baseline population data of the SWFL along the Middle Rio Grande and also to meet Reclamation’s Endangered Species Act (ESA) compliance commitments. There were 221 resident SWFLs documented in 131 territories forming 90 breeding pairs. As in previous years, the San Marcial and Sevilleta reaches were most productive containing 107 and 17 territories, respectively.

Nest monitoring was conducted at all sites where nesting pairs were detected. Nests were monitored for success rates, productivity, and Brown-headed Cowbird (Molothrus ater) (BHCO) parasitism. The San Marcial reach proved most productive, producing 127 nests and fledging at least 197 SWFL young. The Sevilleta reach produced 10 nests and fledged at least 3 SWFL young (fates of 6 nests were unknown). Overall, nest variables (success, predation, BHCO parasitism, and productivity) remained similar to 2004.

Other studies were initiated or continued in 2005. These include: (1) BHCO point counts, (2) livestock grazing study, (3) SWFL habitat suitability assessment, (4) vegetation mapping, and (5) SWFL nest site vegetation quantification study. These studies are designed to provide further insight into potential threats to and habitat requirements of SWFL populations.