Different nesting substrates provide varying degrees of protection from predation ( Roth and Marzluff 1989). Golden Eagles ( Aquila chrysaetos), Prairie Falcons ( Falco mexicanus), Great Horned Owls ( Bubo virginianus), coyotes ( Canis latrans), red foxes ( Vulpes vulpes), and American badgers ( Taxidea taxus) are predators of Ferruginous Hawk eggs and nestlings ( Van Horn 1993, Bechard and Schmutz 1995). Zelenak and Rotella (1997) found that Ferruginous Hawks nesting farther from nests of other raptors produced more young than those nesting closer to other raptors, suggesting reproductive success was negatively influenced by intraspecific and interspecific competition. When Ferruginous Hawks, Red-tailed Hawks ( Buteo jamaicensis), and Swainson's Hawks ( Buteo swainsoni) nest in close proximity, their reproductive success declines ( Schmutz et al. Schmutz (1989) reported that intraspecific and interspecific competition for space occurs between Ferruginous Hawk nesting pairs and other breeding raptor species. Ferruginous Hawks primarily prey on mammals including ground squirrels ( Spermophilus spp.), pocket gophers ( Thomomys spp.), prairie dogs ( Cynomys spp.), and jackrabbits ( Lepus spp.), although birds, reptiles, and insects are taken ( Smith and Murphy 1978, Bechard and Schmutz 1995, Dechant et al. 1981, White and Thurow 1985, Stalmaster 1988, Woffinden and Murphy 1989, Zelenak and Rotella 1997, Ward 2001, Dechant et al. Ferruginous Hawk nesting density and nesting success are closely related to prey abundance and availability ( Smith et al. The reproductive success of Ferruginous Hawks ( Buteo regalis) varies based on prey abundance, competition for space with other breeding raptors, mammalian and avian depredation, and human disturbance. Our results suggest that the level of oil development that occurred during this study did not have an adverse effect on Ferruginous Hawk reproduction the effect of a higher level of oil development was beyond the scope of this study. Avian depredation may have resulted from increased competition among avian predators for scarce prey resources, or from increased use of juvenile Ferruginous Hawks as an alternative prey source by Golden Eagles ( Aquila chrysaetos) in years of low lagomorph abundance. During our study, 17 nestlings and 14 fledglings died 55% were due to avian predators, 16% to mammalian predators, 10% to unknown predators, 16% to natural causes, and 3% to unknown causes. Each nesting pair produced an average of 1.9 nestlings, 1.3 fledglings, and 0.9 dispersed young. Although the Uintah Basin experienced a drought during our entire study, reproductive success was within the range of estimates reported in other studies in the Intermountain West. We hypothesized that reproductive success would be influenced by nesting substrate, abundance of prey, distance to the closest occupied raptor nest, and distance to the closest active well. For three breeding seasons (2002–2004), we measured the number of nestlings, fledglings, and dispersed young that were produced by pairs of Ferruginous Hawks nesting within 2365 km 2 managed by the Bureau of Land Management. We examined factors that potentially influenced reproductive success in Ferruginous Hawks ( Buteo regalis) in the Uintah Basin, Utah, and determined whether oil and gas well development was one of those factors.
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