Buteo regalis

A hawk with a rusty back and shoulders, paler head, and white tail washed with pale rust; white patch at the base of the flight feathers on the upper wing surface; dark legs of adult contrast with whitish underparts; uncommon dark phase lacks dark tail bands; averages 58 cm long, 135 cm wingspan (NGS 1983).

Dark phase differs from dark-phase rough-legged hawk (BUTEO LAGOPUS) by absence of dark tail bands in the former. Immature resembles Great Plains form of red-tailed hawk (BUTEO JAMAICENSIS) but has larger white wing patches and lacks dark bar on leading edge of underwing (NGS 1983).

Open country, primarily prairies, plains and badlands; sagebrush, saltbush-greasewood shrubland, periphery of pinyon-juniper and other woodland, desert. In the southern Great Plains, common at black-tailed prairie dog colonies in winter (Schmutz and Fyfe 1987). Nests in tall trees or willows along streams or on steep slopes, in junipers (Utah), on cliff ledges, river-cut banks, hillsides, on power line towers, sometimes on sloped ground on the plains or on mounds in open desert. Generally avoids areas of intensive agriculture or human activity.

Prefer open grasslands and shrubsteppe communities. Uses native and tame grasslands, pastures, hayland, cropland, and shrubsteppe (Stewart 1975, Woffinden 1975, Powers and Craig 1976, Fitzner et al. 1977, Blair 1978, Wakeley 1978, Lardy 1980, Schmidt 1981, Gilmer and Stewart 1983, Green and Morrison 1983, Konrad and Gilmer 1986, MacLaren et al. 1988, Palmer 1988, Roth and Marzluff 1989, Bechard et al. 1990, Black 1992, Niemuth 1992, Bechard and Schmutz 1995, Faanes and Lingle 1995, Houston 1995, Zelenak and Rotella 1997, Leary et al. 1998). Usually occupy rolling or rugged terrain (Blair 1978, Palmer 1988, Black 1992). High elevations, forest interiors, narrow canyons, and cliff areas are avoided (Janes 1985, Palmer 1988, Black 1992), as is parkland habitat in Canada (Schmutz 1991a).

Landscapes with moderate coverage (less than 50 percent) of cropland and hayland are used for nesting and foraging (Blair 1978; Wakeley 1978; Gilmer and Stewart 1983; Konrad and Gilmer 1986; Schmutz 1989, 1991a; Bechard et al. 1990; Faanes and Lingle 1995; Leary et al. 1998). In North Dakota, hayfields and native pastures were the habitats most often used by both fledglings and adults, whereas cultivated fields rarely were used (Konrad and Gilmer 1986). Fledglings in South Dakota hunted in an area where native hay recently had been cut (Blair 1978). When prey densities were low in big sagebrush (Artemisia tridentata)/grassland habitat, agricultural fields served as important foraging areas (Leary et al. 1998). Foraged extensively in alfalfa (Medicago sativa) and irrigated potato fields in Washington and in alfalfa fields in Idaho during the breeding season presumably because of high prey densities (Wakeley 1978, Leary et al. 1998).

Nest site selection depends upon available substrates and surrounding land use. Ground nests typically are located far from human activities and on elevated landforms in large grassland areas (Lokemoen and Duebbert 1976, Blair 1978, Blair and Schitoskey 1982, Gilmer and Stewart 1983, Atkinson 1992, Black 1992). Lone or peripheral trees are preferred over densely wooded areas when trees are selected as the nesting substrate (Weston 1968, Lokemoen and Duebbert 1976, Gilmer and Stewart 1983, Woffinden and Murphy 1983, Palmer 1988, Bechard et al. 1990). Tree-nesting hawks seem to be less sensitive to surrounding land use, but they still avoid areas of intensive agriculture or high human disturbance (Gilmer and Stewart 1983; Schmutz 1984, 1987, 1991a; Bechard et al. 1990).

In eastern Colorado, nested more frequently in grassland areas than in cultivated areas (Olendorff 1973). In North Dakota, preferred to nest in areas dominated by pasture and hayland (Gilmer and Stewart 1983, Gaines 1985). In southwestern Montana, sagebrush (Artemisia) and grasslands predominated within 100 meters of nests (Atkinson 1992). Ground nests in northern Montana were located in grass-dominated, rolling (more than 10 percent slope) rangeland; in general, cropland and areas with dense (more than 30 percent cover), tall (more than 15.24 centimeters) sagebrush were avoided (Black 1992). In western Kansas, most nests were surrounded by more than 50 percent rangeland and 25-50 percent cropland, although one pair incorporated more than 75 percent cropland in its territory (Roth and Marzluff 1989). The majority of nests (86 of 99) were not in direct view of black-tailed prairie dog (Cynomys ludovicianus) towns, although most nest sites were within 8 kilometers of towns (Roth and Marzluff 1989). In Utah, Idaho, Oregon, and California, preferred native grassland and shrubland habitats over cropland, and preferred areas with no perches (Janes 1985). In Washington, some nests occurred in agricultural fields, but most nests were in areas with higher percentages of grassland, shrubland, and western juniper (Juniperus occidentalis) (Bechard et al. 1990). Nest productivity in Idaho was greater in territories with higher amounts of crested wheatgrass (Agropyron cristatum) fields interspersed with desert shrub than in territories with monotypic stands of crested wheatgrass or shrubland, or with greater amounts of Utah juniper (Juniperus osteosperma), alfalfa, and cropland (Howard 1975). In Nevada, open, rolling sagebrush near the pinyon-juniper interface is the preferred landscape for breeding Ferruginous Hawks (GBBO 2010).

In Alberta, however, cultivated areas (11-30 percent of 4,100 hectare plots) had higher nesting densities than grassland areas with 0-11 percent cultivation (Schmutz 1989). In cultivated areas (20 percent) in northcentral Montana, nests closer to cultivated fields and roads were more successful, presumably because of higher prey densities associated with edge habitats (Zelenak and Rotella 1997). The numbers of fledglings produced in unfragmented rangeland versus a mixture of rangeland and cropland were not significantly different in Nebraska (Podany 1996).

The slope, height, and exposure of nests were mostly similar across the species' range. The mean height of ground nests (on buttes or hills) above the surrounding prairie in South Dakota was less than 10 meters, and nests were oriented toward the south and west, providing access to prevailing winds from the south and west (Blair 1978). Lokemoen and Duebbert (1976) found ground nests in South Dakota were all oriented toward the west. Nests in southwestern Montana were significantly oriented toward the south (Atkinson 1992). Nests on rock outcrops in Montana were built on slopes averaging 62.8 percent and were found on the upper 35 percent of the slope (Atkinson 1992). Ground nests in northern Montana were located either on the top of a small rise or on slopes ranging from 10 to 50 percent (Black 1992). Average height of ground nests below the highest surrounding topographic feature was 10 meters, whereas average height of ground nest sites above the valley floor was 10.4 meters, indicating that nests were placed at mid-elevation sites within the immediate topography (Black 1992). Nests in Wyoming were built on a mean slope of 14.26 degrees, and the mean height of nests was 4.55 meters (MacLaren et al. 1988). In southeastern Washington, 86 percent of nests on outcrops and in western junipers were located less than 10 meters from the ground and had southern or western exposures (Bechard et al. 1990). In Oregon shrubsteppe, nests were in relatively short western juniper trees, were less than 10 meters from the ground, and had large support branches (Green and Morrison 1983). In Washington, Idaho, and Utah, the majority of nests also were less than 10 meters from the ground in western juniper and Utah juniper trees (Woffinden 1975, Fitzner et al. 1977, Woffinden and Murphy 1983). Howard (1975) and Howard and Wolfe (1976) also found Utah juniper trees were important nest substrates in southern Idaho and northern Utah. In Utah, nests were built 2-3 meters from the ground, were most commonly located on the sides or summits of hills, and often had southern or eastern exposures (Weston 1968). Woffinden (1975) found that the majority of nests in Utah were on slopes ranging from 15 to 80 degrees with a mean of 42.5 degrees.

Density and productivity are closely associated with cycles of prey abundance (Woffinden 1975; Powers and Craig 1976; Smith and Murphy 1978, Smith et al. 1981; Gilmer and Stewart 1983; Houston and Bechard 1984; White and Thurow 1985; Palmer 1988; Schmutz 1989, 1991a; Schmutz and Hungle 1989; Bechard and Schmutz 1995). Estimates of home range size vary from 3.14 to 8.09 square kilometers in the Columbia River Basin and Great Basin regions of the western U.S. (Janes 1985). The average home range was 90.3 square kilometers in Washington, and the variability in home range was significantly related to distance from the nest to the nearest irrigated agricultural field (Leary et al. 1998). One male that nested closest to the surrounding agricultural fields had the smallest home range, whereas another male nesting farthest from the agricultural fields had the largest home range. In Utah, mean home range recorded of 5.9 square kilometers (Smith and Murphy 1973). An area of up to 21.7 square kilometers may be required by one pair for hunting in Idaho (Wakeley 1978). Up to 8-10 nests per 100 square kilomters if local conditions are favorable (see Palmer [1988] for density data in several areas). In 11 study areas, mean nearest neighbor distance was 3.4 kilometers (range 0.8-7.2); in six study areas the mean home range size was 7.0 square kilometers (range 3.4-21.7) (Olendorff 1993). Recent studies in Idaho (McAnnis 1990) and Washington (Leary 1996) found average home ranges of 7.6 square kilometers (minimum convex polygon)/19.4 square kilometers (95 percent harmonic mean) and 70 square kilometers (95 percent minimum convex polygon)/31 square kilometers (85 percent adaptive kernel), respectively.

First year mortality generally is around 66 percent in the Great Plains region (Schmutz and Fyfe 1987).

Occur on breeding areas from late February through early October (Weston 1968, Olendorff 1973, Maher 1974, Blair 1978, Smith and Murphy 1978, Gilmer and Stewart 1983, Schmutz and Fyfe 1987, Palmer 1988, Bechard and Schmutz 1995). See Palmer (1988) and Hall et al. (1988) for egg dates in different areas. Clutch size usually is two to four. Incubation lasts about 32-33 days, mostly by female; male provides food. Young fledge in 35-50 days (males before females), depend on parents for several weeks more. No evidence that yearlings breed. Renesting within the same year is rare (Woffinden 1975, Palmer 1988) even when clutch is lost. Territory and nest site reoccupancy is common and one of several nests within a territory may be used in alternate years (Davy 1930, Weston 1968, Olendorff 1973, Blair 1978, Smith and Murphy 1978, Palmer 1988, Roth and Marzluff 1989, Schmutz 1991b, Atkinson 1992, Houston 1995). Mate fidelity also is common. (Schmutz 1991b). Clutch size, fledging rate, and/or breeding density tend to vary with prey (especially jackrabbit [LEPUS SPP.] or ground squirrel [SPERMOPHILUS SPP.]) availability.