Nesting pair density and abundance of ferruginous hawks (Buteo regalis) and golden eagles (Aquila chrysaetos) from aerial surveys in Wyoming

Abstract Raptors that inhabit sagebrush steppe and grassland ecosystems in the western United States may be threatened by continued loss and modification of their habitat due to energy development, conversion to agriculture, and human encroachment. Actions to protect these species are hampered by a lack of reliable data on such basic information as population size and density. We estimated density and abundance of nesting pairs of Ferruginous Hawks (Buteo regalis) and Golden Eagles (Aquila chrysaetos) in sagebrush steppe and grassland regions of Wyoming, based on aerial line transect surveys of randomly selected townships. In 2010 and 2011, we surveyed 99 townships and located 62 occupied Ferruginous Hawk nests and 36 occupied Golden Eagle nests. We used distance sampling to estimate a nesting pair density of 94.7 km2 per pair (95% CI: 69.9–139.8 km2) for Ferruginous Hawks, and 165.9 km2 per pair (95% CI: 126.8–230.8 km2) for Golden Eagles. Our estimates were similar to or lower than those from other stud...