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from the Grand Canyon in 1988 were 11.4t to 12.7t thinner than pre-DOE controls. In addition to pesticide concentrations, competition with other raptors has been considered as a possible cause of peregrine falcon population declines; however, Porter and White (1973) examined peregrine and prairie falcon interactions and concluded that competition was not important. Impacts of the test flow Most wintering waterfowl on which peregrine falcons feed will have migrated from Grand Canyon by late March; however, mallard and late migrating gadwall and American widgeon are still likely to be common (Stevens, personal communication). Springtime food sources (swifts, swallows and bats) should be present in large numbers at that time of year (Stevens, personal communication), and are only indirectly influenced by dam operations. Therefore, peregrine falcons will not lack food,resources during the proposed high release. The test flow will have no effect on peregrine falcons in the Colorado River downstream from Glen Canyon Dam. SOUTHWESTERN WILLOW FLYCATCHER SPECIES ACCOUNT Distribution and Abundance The southwestern willow flycatcher (SWWF; Tyrannidae: RmnirlnnAX trail1i extimls) is a Neotropical migrant with a broad breeding range, extending from Nova Scotia to British Columbia and south to Baja California. The SWWF is an obligate riparian insectivore (Hunter et al., 1987), preferring habitat near open water (Gorski 1969; Sogge 1995). The historic breeding range of the SWWF includes Arizona, New Mexico, southern California, and southern portions of Nevada, Utah, and perhaps southwestern Colorado, and extends east into western Texas (U.S. Fish and wildlife Service 1993). It winters from Mexico to Panama, with historical accounts from Colombia (Phillips 1948). The SWWF is distinguished from other subspecies by distribution, morphology and color, nesting ecology, and possibly by song dialect (Phillips 1948, Aldrich 1953, King 1955, Sogge 1995). Although never common, ~. ~. extimus population declines have been noted for nearly 50 years, corresponding with loss and modification of riparian habitats (Phillips 1948). Southwestern riparian ecosystems support a rich avian fauna (Johnson and Haight 1987) and habitat changes have resulted in reduction or extirpation of many avian species (Hunter et al., 1987). Modification and fragmentation of these systems through development and livestock grazing have precipitated devastating changes to SWWF populations. Destruction of native willow/cottonwood vegetation has provided opportunity for invasion by non- native plant species. notably saltcedar. Habitat fragmentation and modification has benefitted some southwestern avian species, especially cowbirds (Molothrus spp.) , which parasitize SWWF nests, contributing to the precipitous population declines of SWWF (Brown 1994, Johnson and Sogge 1995, 15