Technical Report

Literature Review on Water Needs of the Southwestern Willow Flycatcher

URL: https://webapps.usgs.gov/mrgescp/documents/Copeland%20et%20al_2009_Literature%20Review%20on%20Water%20Needs%20of%20the%20SWFL.pdf

Date: 2009/01/23

Author(s): Copeland S.L., Beane R.D., Paradzick C.E., Sommers C.L.

Publication: Report prepared for the U.S. Bureau of Reclamation, 57 p.

Abstract:

Since the Southwestern Willow Flycatcher (Empidonax traillii extimus; hereafter “SWFL”) was listed as federally endangered in 1995, its distribution, habitat use, and nest success have been studied extensively. General habitat characteristics have been identified, including dense vegetation and the proximity of breeding locations to surface water or soil moisture (Sogge and Marshall 2000, USFWS 2002). Water availability affects food availability, the density and vigor of riparian vegetation, and microclimate within the habitat that SWFLs use for nesting (USFWS 2005), and may affect reproductive success including predation and parasitism rates.

Bureau of Reclamation (Reclamation), one of the main water managers in the Southwest, would like to improve its understanding of the water-related requirements for SWFLs to develop habitat restoration projects and manage limited water resources. In 2003, Reclamation, along with Army Corps of Engineers, State of New Mexico, and the Middle Rio Grande Conservancy District, consulted with the U.S. Fish and Wildlife Service (USFWS) on water operations of the Middle Rio Grande in New Mexico (Reclamation 2003). According to the Biological Opinion (USFWS 2003), Reclamation must maintain moist soils throughout the breeding season in the delta of Elephant Butte Reservoir, an area with a large population of breeding SWFLs, and conduct hydrological monitoring.

With new information available related to hydrology, Reclamation’s goal was to conduct a comprehensive literature review focusing on water resources needed for SWFL territory establishment (or habitat selection) and nest success. ERO Resources Corporation (ERO), under contract with Reclamation, screened 92 reports for direct and indirect relationships between hydrology and SWFL habitat use or demographics. Few reports were peer reviewed and methods varied greatly, making comparisons difficult. Of 78 independent studies, 27 contained information on direct relationships between hydrology and SWFLs. Only 10 reports related SWFL demographics to hydrology. Three studies examined effects of seasonal water availability on nest success. Due to the paucity of information, reports also were screened for descriptions on seasonal water availability.