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. . Grand Canyon by late March; however, mallard and late migrating gadwall and American widgeon are still likely to be common (Stevens et al. 1997a, 1998). Springtime food sources (swifts, swallows and bats) should be present in large numbers at that time of year (Stevens et al. 1998), and are only indirectly influenced by dam operations. Therefore, peregrine falcons will not lack food resources during the proposed high release. Reclamation concludes that BHBFs between May and July will have no effect on peregrine falcons in the Colorado River downstream from Glen Canyon Dam. SOUTHWESTERN WILLOW FLYCATCHER SPECIES ACCOUNT Distribution and Abundance Arizona has experienced the sharpest decline in SWWF numbers. SWWF formerly bred throughout the state at high and low elevations. For example, a 1931 breeding record exists from the south rim of the Grand Canyon (Brown et aI., 1984), indicating that this taxon bred at high elevations, even at the northern edge of its range. By 1987, the State population was estimated at less than 25 pairs (Unitt 1987; U.S. Fish and Wildlife Service 1993), but much habitat was not surveyed. At least 52 territories or active nests were reported during extensive surveys in 1993 in Arizona (Muiznieks et al. 1994), and at least 62 active nests were located during a more thorough inventory in 1994 (Sferra et al. 1995). In Arizona, there were approximately 113 SWWF pairs in 1996 (Sferra et al. 1997). From 1974 through 1996 the Grand Canyon population was detected between Colorado River miles 47 and 71 (Unitt 1987, Sogge et al. 1995, 1997). In its recent proposal the Service included the Colorado River from River Mile 39 to River Mile 71.5 as critical habitat (U.S. Fish and Wildlife Service 1993), and stipulated in a subsequent final rule that defines such habitat as that "within 100 meters of the edge of areas with surface water during the May to September breeding season and within 100 meters of areas where such surface water no longer exists owing to habitat degradation but may be recovered with habitat rehabilitation" (U.S. Fish and Wildlife Service 1997). The boundary of this area in Grand Canyon includes the main Colorado River channel and associated side channels, backwaters, pools and marshes. In 1996 Sogge et al (1997) reported three singing SWWF, but only one successfully breeding pair along the Colorado River in upper Grand Canyon. The single pair apparently fledged two young. In 1997 the single SWWF nest in upper Grand Canyon failed to produce young because of cowbird brood parasitism (M. Sogge, U.S. Geological Survey Biological Resources Division, personal communication). A single SWWF nest near mile 265 in 1997 produced two young (Grand Canyon Monitoring and Research Center 1997). Other recent reports of SWWF breeding in the lower Colorado River basin have stimulated additional research there. The Service's 1996 B.O. on the BHBF defined several measures to mitigate impacts on 1998 GCD Beach/Habitat Building Flow 19 Biological Assessment