Ferruginous hawks (Buteo regalis) were studied in central North Dakota on a 1,259-km2 intensive study block and on a surrounding study area (16,519 km2) from 1977 to 1979. A total of 629 occupied nests was examined. Highest nest densities (0.08 nest/km2) were in the Missouri Coteau in 1979. Few nests were found on the more intensively cultivated Drift Plain. We estimated the breeding population in the study area each year using 148 sample plots (? = 440 nesting pairs). Pairs that nested on the ground selected only sites on rugged landforms in isolated areas, mostly end and dead-ice moraines. Land use within 1.0 km of nests was mostly (76.5%) pasture and haylands. About 95% of the area around ground nests was grassland. Tree and tower nesting birds appeared less sensitive to surrounding land use. Pairs on the intensive study block used a wide variety of nest sites including trees (63.6%), ground (20.9%), power line towers (8.0%), haystacks (5.4%), and rock piles, utility poles, and shrubs (2.1%). Reoccupancy rates were higher (63.7%) for tower nests than for other sites. Nest success was related to the type of nest site and was highest (86.7%) in certain power line towers. Mean number of young fledged per occupied nest was highest (2.8) for ground nests. Summer storms were a major cause of loss; tree nests were particularly vulnerable. Richardson's ground squirrels (Spermophilus richardsonii) were taken as prey most often. Ferruginous hawks are closely associated with grasslands, particularly native prairie. J. WILDL. MANAGE. 47(1): 146-157 Resource managers have identified the need to gather baseline data on raptors inhabiting portions of the Northern Great Plains subjected to disturbances from energy development (D. L. Evans, unpubl. rep., U.S. Fish and Wildl. Serv., Jamestown, N.D., 1980) and intensive agriculture (Stewart 1975). Because raptors are indicators of environmental quality (Odum 1971), knowledge of their densities and productivity can also be used to assess ecosystem condition. The ferruginous hawk is a major component of the raptor fauna in much of western North America and has been the focus of a number of recent studies (Olendorff 1973; Howard 1975; Lokemoen and Duebbert 1976; Fitzner et al. 1977; Smith and Murphy 1978; Wakeley 1978a,b; Lardy 1980; Schmutz et al. 1980; Powers 1981; Blair and Schitoskey 1982). Despite these studies, its population status is largely unknown in most areas of the breeding range (Evans 1982). Historical data and casual observations indicate the ferruginous hawk is a common breeder in central North Dakota (Stewart and Kantrud 1972, Stewart 1975). We studied the ferruginous hawk from spring 1977 through summer 1979 to evaluate density, productivity, habitat preference, nest site selection, and prey use of the species in North Dakota. We acknowledge the field assistance of B. A. Hanson, T. J. Moser, D. L. Pieske, R. N. Rosenfield, J. L. Sease, and particularly P. M. Konrad and D. L. Evans. T. Gatz provided information on some nest locations. R. Schafer, M. Edman, and pilot T. Cochran (Minnkota Power Coop., Inc., Grand Forks, N.D.) arranged for the use of a helicopter on power line surveys. D. A. Davenport and C. L. Nustad provided computer programming and A. M. Frank ' Present address: Wildlife Research Field Station, U.S. Fish and Wildlife Service, 6924 Tremont Road, Dixon, CA 95620. 146 J. Wildl. Manage. 47(1):1983 This content downloaded from 40.77.167.43 on Tue, 21 Jun 2016 05:24:41 UTC All use subject to http://about.jstor.org/terms FERRUGINOUS HAWK POPULATIONS * Gilmer and Stewart 147 and D. H. Johnson assisted with statistical design and analysis. K. Rankin, R. Nakamoto, J. Hicks, and P. N. Konrad assisted with data preparation. E. Bartels provided library services. A. B. Sargeant, R. R. Olendorff, R. P. Howard, J. W. Wiley, and A. M. Frank kindly reviewed the manuscript. W. R. Dryer provided technical editorial services. Support for this study was provided by the U.S. Fish and Wildlife Service.