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<br />. <br /> <br />. <br /> <br />conclude their spawning run in Nankoweap Creek in April as water temperatures warm <br />(Leibfried and Montgomery 1993), and remaining bald eagles no longer have access to <br />that food source. <br /> <br />BHBFs from late May through July will have no negative effect on the bald eagle <br />population in the Colorado River in Grand Canyon because this migratory species is <br />unlikely to be present. <br /> <br />PEREGRINE FALCON SPECIES ACCOUNT <br /> <br />Distribution and Abundance <br /> <br />The Grand Canyon peregrine population was low in the mid-1970's (Ellis and Monson <br />1989), but increased dramatically in the 1980's, following recovery efforts by the Service <br />(1984; Glinski 1993). At present, the Grand Canyon supports the largest breeding <br />population of peregrine falcons in the coterminous United States (Brown et al. 1991a, <br />1992). Surveys for nesting peregrine falcons in 1988 and 1989 revealed 28 and 58 <br />pairs, in 15% and 24% of the park, respectively. Habitat-based estimation of the <br />potential number of peregrine falcons in Grand Canyon suggested that as many as 96 <br />pairs existed in Grand Canyon in 1989. <br /> <br />Life Requisites <br /> <br />Peregrine falcons feed on more than 40 species of birds and several small mammals <br />(Porter and White 1973, Stevens et al. 1998). Hunting areas included marshes or <br />narrow tongues of streamside vegetation, and peregrine falcons may forage up to <br />17 miles from nest sites. Peregrine falcon diet at nest sites in national parks in <br />southern Utah included small and medium-sized birds, especially including white- <br />throated swifts, large shorebirds and Clark's nutcracker (Burnham 1987). <br /> <br />In Grand Canyon, peregrine falcons feed on waterfowl, swifts, swallows and bats <br />(Brown 1991a, Stevens et al. 1998), many of which feed on invertebrate species <br />(especially Diptera) that emerge out of the Colorado River (Stevens et al. 1997c). <br />Therefore, dam operations that influence aquatic macro-invertebrate populations exert, <br />at most, only indirect impacts on peregrine falcons. <br /> <br />Peregrine falcons breed up to 3,130 m elevation, typically on ledges on steep cliff faces <br />(U.S. Fish and Wildlife Service 1984). The mean distance between nest sites along the <br />South Rim of Grand Canyon varied from 3.5 to 5.0 linear miles, with minimum distances <br />of 1.8 linear miles (Brown 1991a, 1992). The breeding season in Grand Canyon <br />extends from February to July. <br /> <br />Impacts of BHBF <br /> <br />Most wintering waterfowl on which peregrine falcons feed will have migrated from <br /> <br />1998 GCD Beach/Habitat Building Flow 18 <br /> <br />Biological Assessment <br />