Abstract
We examined habitat use, prey capture, and foraging success of Bald Eagles (Haliaeetus leucocephalus) in winters of 1990 and 1991 to evaluate influences of hourly fluctuating river flows from Glen Canyon Dam along the Colorado River in Grand Canyon National Park, Arizona. Patterns of habitat use were strongly dependent upon fluctuating flows in both years. Foraging in river, shore, and isolated pool habitats decreased to 0% at flows > 568 m 3 sec -1 , whereas foraging in adjacent creek habitat increased to 100%. More foraging attempts occurred farther from the river in adjacent creek habitat as river flows increased, but this did not influence foraging success in creek habitat. Rainbow trout (Oncorhynchus mykiss) stranded by fluctuating river flows comprised 12% and 19% of eagle prey captures in 1990 and 1991, respectively. Foraging success in river habitat decreased in 1990 as river flows increased from 284 m 3 sec -1 (39%); foraging success in river habitat was independent of fluctuating flows in 1991. Low river flows exerted neutral or positive influences on eagle habitat use and prey capture, whereas high river flows reduced eagle foraging habitat diversity, lowered foraging success in river habitat, and restricted foraging opportunities. Management strategies to limit high river flows and sustained flooding during peak eagle concentration may benefit wintering eagles.
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