Factors Influencing Reproductive Success Of Ferruginous Hawks in the Uintah Basin, Utah

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. 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 km² managed by the Bureau of Land Management. 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. 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. Each nesting pair produced an average of 1.9 nestlings, 1.3 fledglings, and 0.9 dispersed young. 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. 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. 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.