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Bald eagles concentrate at Nankoweap Creek in Grand Canyon, during the spawning rund of non- native trout to take advantage of a readily available and abundant food source. During the remaining portions of the year,. eagles have been observed as distributed through the canyon in relatively small numbers. At N ankoweap Creek, wintering bald eagles preferentially capture rainbow trout in the shallow creek, rather than in the mainstream where foraging success is low (Brown 1993, Sogge et aI., 1995). Bald eagles at Nankoweap Creek prefer roosting and feeding areas that are relatively free of vegetation. The eagle population there consists of all age classes, with considerable piracy and other interactions between individuals (Brown and Leibfried 1992). The ease and relative safety offoraging in Nankoweap Creek aff'ordswintering bald eagles at Nankoweap Creek the opportunity to accumulate energy reserves needed for their long, northward migration flights and initiation of nesting. Effects of the Proposed Action on Bald Eagle The proposed action should not alter the food base or habitat of the bald eagle. Only resident birds are expected to present at this time, with the majority bald eagle that winter in the canyon only beginning to migrate to the area During the portion of this 48 hour test when the releases are at power plant capacity, foraging in the main stem Colorado River may be more difficult. Current weather conditions would most likely be similar to the fluctuations the birds will experience with the October test flow. The test flow will have no effect on the wintering bald eagle population in the Colorado River in Grand Canyon. PEREGRINE FALCON Distribution and Abundanu The peregrine falcon (Falconidae: ~ perearinu~) is a federally listed endangered raptor, which has declined dramatically as a result of the biological concentration of pesticide residues in prey species, and resulting eggshell thinning (U.S. Fish and Wtldlife Service 1984) and the increase in food base in Grand Canyon. The population in the Rocky Mountain/southwest region declined from 180 pairs prior to 1915 to 55 pairs in 1983, largely as a result ofDDT/DDE thinning of . eggshells (U.S. Fish and Wtldlife 1984). The Grand Canyon peregrine population was low in the mid-1910's (Ellis and Monson 1989), but increased dramatically in the 1980's, following recovery efforts by the U.S. Fish and Wtldlife Service (1984). At present, the Grand Canyon supports the largest breeding population of peregrine falcons in the cotenninous United States (Brown 1991a). Surveys for nesting peregrine falcons in 1988 and 1989 revealed 28 and 58 pairs, in 15% and 24% of the park, respectively. Habitat-based estimation of the potential number of peregrine falcons in Grand Canyon suggested that as many as 96 pair existed in Grand Canyon in 1989. 23