Technical Report

2004 Southwestern Willow Flycatcher Study Results

URL: https://webapps.usgs.gov/mrgescp/documents/Reclamation_2005_2004SWFLReport.pdf

Date: 2005/04/01

Author(s): Reclamation

Publication: U.S. Bureau of Reclamation Report, 60 p.

Abstract:

The Southwestern Willow Flycatcher (Empidonax traillii extimus) (SWFL) is a State-listed and federally endangered subspecies of the Willow Flycatcher (Empidonax traillii) (WIFL). It is an insectivorous, Neotropical migrant that nests in dense riparian or wetland vegetation in the Southwestern United States (Figure 1). SWFLs generally arrive at their breeding grounds between early May and early June; by late July or August, they depart for wintering areas in Mexico, Central America, and northern South America (Sogge et al. 1997, USFWS 2003).

Recent studies indicate that SWFL populations have declined across their range (USFWS 2002). The primary causes of declining populations are likely habitat loss or modification and brood parasitism by the Brown-headed Cowbird (Molothrus ater) (BHCO) (USFWS 2002). The U.S. Fish and Wildlife Service (USFWS) officially listed the SWFL as endangered in February 1995 (USFWS 1995). The SWFL is also listed as endangered or a species of concern by the States of Arizona, California, Colorado, New Mexico, Texas and Utah (Sogge et. al. 1997, TPWD 2005). A recovery plan for the SWFL was finalized in August 2002. To accompany the recovery plan, a series of issue papers associated with the recovery of the endangered SWFL has also been prepared by the Recovery Team. These papers address current issues and recommend management alternatives in regard to BHCO parasitism, livestock grazing, water management, exotic vegetation, habitat restoration, fire management, and recreational impacts (USFWS 2002). In October 2004, USFWS proposed Critical Habitat for the SWFL along the Middle Rio Grande from “4.2 miles north of the intersection of Interstate 25 and 40 downstream to the overhead powerline near Milligan Gulch at the northern end of Elephant Butte State Park” (USFWS 2004).

Field surveys are conducted to determine the distribution and abundance of the endangered SWFL during the relatively brief breeding season when they become a seasonal resident of the Southwestern United States. Bureau of Reclamation (Reclamation) personnel have conducted presence/absence surveys and nest monitoring during the May to July survey season within the Rio Grande Basin since 1995. In 1994, the New Mexico Natural Heritage Program (NMNHP 1994) conducted presence/absence surveys and nest monitoring within the San Marcial reach under a contract with the U.S. Army Corps of Engineers.