Technical Report
2007 Southwestern Willow Flycatcher Study Results
Date: 2008/05/01
Author(s): Moore D., Ahlers D.
Publication: Bureau of Reclamation Report, 64 p.
Abstract:
During the summer of 2007, 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 200 kilometers of the Middle Rio Grande (MRG) in New Mexico adjacent to Velarde 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 403 resident SWFLs documented in 232 territories forming 171 breeding pairs. As in previous years, the San Marcial reach of the river was by far the most productive containing 197 territories and 153 pairs.
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 220 nests and fledging 315 SWFL young. The Sevilleta reach produced 6 nests and fledged 11 SWFL young. Overall, nest variables (success, predation, BHCO parasitism, and productivity) remained similar to the past several years.
Other studies were initiated or continued in 2007. These include: (1) BHCO point counts, (2) livestock grazing study, (3) SWFL nest-site vegetation quantification study, and (4) SWFL nesting hydrology study. These studies are designed to provide further insight into potential threats to and habitat requirements of SWFL populations. Aerial photos of the Rio Grande floodplain from Elephant Butte Reservoir to Bernardo were also taken during summer 2007 and will be used to update vegetation maps and the SWFL habitat model in 2008.