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. . the SWWF in Grand Canyon. Stevens et al. (1996) studied habitat changes at four historic SWWF nest sites in Grand Canyon. Fluvial marshes associated with these sites were dominated by common reed, horsetail and cattail. SWWF research activities associated with that BHBF included verifying stage-to-discharge relations, quantifying flow depth and velocity at nest sites, and determining nest site and foraging habitat structure, litter/understory characteristics, and nesting success. The 1996 BHBF impacts on Grand Canyon SWWF habitat were reported by Stevens et al. (1996). Nest stand vegetation impacts were nominal: two stands were slightly scoured, and three sites sustained a slight reduction in ground cover and/or branch abundance at <0.6 m above the ground; however, no reduction in branch abundance or alteration of stand composition occurred, and the BHBF did not inundate the bases of any historic nest trees. Impacts on marsh foraging habitats were more severe, with decreases in area of 1 % to >72%. Two of four SWWF sites regained vegetated area during the summer of 1996, while two other marshes sustained slight additional losses in cover through the 1996 growing season. The species has been given special protection status by the Game and Fish Department in Arizona. Life Requisites SWWF arrive in the Grand Canyon area in mid-May, but may be confused with another subspecies, the more common E.t. brewsteri, which migrates through to more northern breeding grounds (Aldrich 1951; Unitt 1987). E.t. brewsteri sings during migration, making sub-specific distinctions difficult until mid-June (Brown 1991b). Males arrive earlier than females and set up territories. The characteristic territorial song is a "fitz- bew," most frequently heard in the morning before 10 AM (Tibbitts et aI., 1994). There is little evidence that the four subspecies may be differentiated by characteristics of this song (McCarthey, et al. 1997). The SWWF in Grand Canyon occupy sites with average vegetation canopy height and density (Brown and Trossett 1989). SWWF commonly breed and forage in dense, multistoried riparian vegetation near surface water or moist soil (Whitmore 1977, Sferra et aI., 1995), along low gradient streams (Sogge 1995). Nesting in the Grand Canyon typically occurs in non-native Tamarix approximately 4-7 m tall (13-23 feet), with a dense volume offoliage 0-4 m from the ground (Tibbetts et aI., 1994). SWWF commonly and preferentially nest in saltcedar in upper Grand Canyon (Brown 1988), and nested in saltcedar in Glen Canyon before completion of the Glen Canyon Dam (Behle and Higgins 1959). Although habitat is not limiting in Grand Canyon (Brown and Trossett 1989), required patch size is not known. The 1997 nesting record from lower Grand Canyon demonstrates that this species can colonize new habitat; however, that habitat is influenced by Lower Basin Lake Mead management. Present data indicate no impacts 1998 GCD Beach/Habitat Building Flow 20 Biological Assessment