Publication

2022 Middle Rio Grande Southwestern Willow Flycatcher Study Results

URL: https://webapps.usgs.gov/mrgescp/documents/Moore-and-Root_2023_2022-MRG-SWFL-Study-Results.pdf

Date: 2023/03/01

Author(s): Moore D., Root S.

Publication: Prepared by U.S. Bureau of Reclamation, 49 p.

Abstract:

During the summer of 2022, the Bureau of Reclamation (Reclamation) conducted surveys and nest monitoring of the Federally-listed endangered Southwestern Willow Flycatcher (SWFL). The surveys were completed in six distinct reaches along approximately 99 river miles of the Rio Grande in New Mexico between the Isleta Pueblo and Elephant Butte Reservoir. Due to difficulties in hiring temp employees, certain reaches were not surveyed in their entirety, but priority sites were selected in order to meet Reclamation’s, the Middle Rio Grande Conservancy District’s, and the New Mexico Interstate Stream Commission’s project compliance needs. Certain sites were also selected to contribute to current baseline population data, monitor population trends, and determine the current distribution of SWFLs along the Middle Rio Grande. During 2022 surveys, 928 resident SWFLs were documented. These residents formed 424 pairs and established 504 territories. As in previous years, the San Marcial Reach of the Rio Grande was by far the most productive supporting 352 territories and 302 pairs. However, comparisons to previous years’ data are difficult due to the reduced survey effort. The Bosque del Apache Reach supported 35 territories, a slight decrease from 2021 when 39 territories were recorded. The Belen Reach provided 95 territories, 10 more than were recorded in 2021. Overall, territory numbers in the Middle Rio Grande have increased dramatically during the past three years and were greater in 2022 than during any year since surveys began in 1996.

Additionally, nest searching and monitoring were conducted in occupied sites and nest fates were often determined. Nests were monitored for success rates, productivity, depredation, abandonment and Brown-headed Cowbird parasitism. The San Marcial Reach again provided the most productive habitat, where 398 nests and 374 SWFL fledglings were documented. Within the Belen Reach, 108 SWFL nests which fledged 106 SWFL young were documented. Overall nesting success for the Middle Rio Grande was 49 percent.