Abstract
Glen Canyon Dam has restructured the ecology of the Colorado River through the Grand Canyon causing significant changes to native riparian habitat. The absence of scouring flood events has allowed colonization of riparian vegetation between the old and new high water lines. This has created substantial stands of riparian and marsh habitat for resident and migrant birds. While some bird species have been shown not to breed in the stands of invasive vegetation, most riparian bird species have responded positively to it. Over-wintering bald eagle populations have increased in the Grand Canyon, primarily as a result of robust non-native trout populations below Glen Canyon Dam. Other human land use practices adjacent to the canyon, such as grazing and recreation, have increased Brown-headed Cowbird populations. The Brown-headed Cowbird is a nest parasite and threatens breeding birds such as the federally endangered Southwestern Willow Flycatcher along the river corridor. Avian diversity and abundance has increased following construction of the dam. Increases in waterfowl densities, due to increased open water and marsh habitats, serve as an abundant food source for the recovering Peregrine Falcon. Invasive and highly flammable tamarisk has instilled a fire regime previously absent, which threatens individuals and breeding bird populations and further perpetuates the loss of native willow- cottonwood vegetation assemblages. Management may now be necessary to maintain stable avian communities within the Grand Canyon.