Southwestern Willow Flycatcher- EP

CRE AT-RISK SPECIES VIGNETTES – Larry Stevens

• Southwestern Willow Flycatcher
• The southwestern willow flycatcher (SWWF; Empidonax trailii extimus Phillips 1948) wa listed as endangered in 1993.
• It is a small, greenish flycatcher with white wing bars, and has an upright roosting posture.
• Like the other three subspecies of willow flycatcher, it has a distinctive “fitz-bew” call. Originally ranging from near sea level to over 8,500 ft in elevation, SWWF occurred throughout Arizona and New Mexico, and in southern Texas, California, Nevada, and Utah.
• The flycatcher commonly nests from 2-5 m above the ground, often adjacent to, or over water.
• Intensive surveys and monitoring over the past two decades have revealed 300-500 SWWF nesting pairs throughout its historic range.
• In Grand Canyon, a predam nesting record was reported at Lees Ferry, four pairs nested between Miles 50-71 until about the Year 2000, and nesting occurred along Havasu and Spencer Creeks and at several riparian sites near uppermost Lake Mead.
• However, no nesting pairs have been documented in recent years.
• Nearly all nests in Grand Canyon have been in tamarisk, despite the availability of nearby, apparently suitable native vegetation.
• Typically, more than 80% of the nests found in Arizona each year occur in tamarisk, prompting the U.S. Fish and Wildlife Service to declare some tamarisk-dominated reaches as critical SWWF habitat.
• Reasons for the decline of SWWF include degradation of winter habitat in Central America and breeding habitat in the Southwest, as well as brood parasitism by brown-headed and bronzed cowbirds (Molothrus ater and M. aeneus, respectively).
• Cowbirds pitch SWWF eggs from the nest, replacing them with their own eggs, and the SWWF may raise the cowbirds as their own young. The recent invasion of tamarisk leaf beetle in northern Arizona severely threatens remaining SWWF with further loss of habitat.