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002488 backwaters, and at the waters edge in the Grand Canyon (Tibbetts et aI., 1994). SWWF return to wintering grounds in August and September (Brown 1991b), but neither migration routes nor wintering areas are well known. Birds sing and perhaps defend foraging territories in Central America during winter, and winter movement may be tied to water availability (Gorski 1969). Threats to SWWF on the wintering grounds are poorly documented, but habitat losses in Latin America may be a major factor in the decline of this species. Impacts of BHBF(s) BHBF's that are conducted before May will have no substantial direct effect on the SWWF popufation along the Colorado River in Glen, Marble and upper Grand canyons because the birds do not establish territories until that time. BHBF's during the breeding season are also unlikely to affect the SWWF population because SWWF nest several meters up in tamarisk trees that stand at or above the 45,000 cfs. In upper Grand Canyon, SWWF generally nest in saltcedar trees and nest trees typically lie above the 45,000 cfs stage. The saltcedar stands in which SWWF nest, are unlikely to sustain direct damage from BHBF(s). The saltcedar trees in which the SWWF presently nest survived the >92,600 cfs flows of 1983 as well as the 1996 BHBF (Stevens et al. 1996), and are therefore unlikely to be scoured by one or more brief, 45,000 cfs BHBF's. The wetlands and low-lying areas near SWWF nesting habitats and in which they occasionally forage, are likely to continue to be affected by BHBF's. Impacts to associated wetlands ranged from 1 % to >72% from the 1996 BHBF, and impacts on those sites persisted through the 1996 growing season (Stevens et al. 1996). Although those habitats were strongly affected by the 1996 flood;.actual impacts on SWWF food resources remain undocumented. We have little information on how important these backwater habitats may be in producing a sustainable forage base for SWWF while they are feeding young in the nest. SWWF forage on adult, terrestrial (non-aquatic) flying invertebrates, populations which are unlikely to be affected by a brief BHBF, and which are likely to recover promptly after the event. Aquatic Food Base The phytobenthic community is dominated by Cladophora glomerata and submergent macrophytes with additional constituents including other filamentous green algae and red algae. Cladophora and submergent macrophytes provide mucous-free substrates for diatoms that are a food source for macroinvertebrates and fishes (Blinn et al1992; Hardwick et al. 1992; Stevens et al. 1998). Elements that affect Cladophora and aquatic macrophyte densities include discharge patterns (fluctuating vs. steady flows), flow volume, nutrient inflow concentrations from Glen Canyon Dam, time of year, time since last disturbance, and light availability (i.e., turbidity) (Angradi et al, 1992; McKinney et al1996, 1997; Shannon et al1996). Each of these separately and in combination can influence biomass of this species and concomitantly associated invertebrate biomass. The general pattern of growth for Cladophora, based on monthly sampling in the Lees Ferry Reach, is that biomass is lowest in January and shows a gradual increase such that by June and July, biomass reaches maximum values (Ayers and McKinney 1996a; Shannon et al1996). This pattern coincides with increased light availability allowing longer days for photosynthesis and growth. Other algal constituents show a similar pattern. Biomass densities decrease by August