Montana Field Guide

Ferruginous Hawks have rusty backs and shoulders, pale heads, and white tails washed with pale rust. They have a white patch at the base of the flight feathers on the upper wing surface. Their wings are brown above and white below. The rusty legs of the adult form a dark V contrasted with whitish underparts. Ferruginous Hawks usually appear very light-colored when viewed from a distance. The uncommon dark phase lacks dark tail bands and are dark brown on the body, but still have the whitish tail. The species averages 58 cm long with a 135 cm wingspan. Immature birds are brown instead of rust, and have brown streaking on the undersides.

For a comprehensive review of the conservation status, habitat use, and ecology of this and other Montana bird species, please see Marks et al. 2016, Birds of Montana.

Krider's Red-tailed Hawk (B. jamaicensis) is brown, not rust, has white feathers on the legs, dark shoulder patches, and a dark band across the belly. The dark phase Ferruginous Hawk differs from the dark phase Rough-legged Hawk (B. lagopus) by the absence of dark tail bands in the former. Immature Ferruginous Hawks resemble the Great Plains form of the Red-tailed Hawk, but have larger white wing patches and lack the dark bar on the leading edge of the underwing.

Ferruginous Hawks breeding in Montana are entirely migratory (Bechard and Schmutz 1995). Fall migration begins in August and continues into early September. Young birds will migrate south earlier than, and independent of, adults. The latest recorded observation date for Ferruginous Hawks in eastern Montana is in October, from 3 records (Saunders 1921, Montana Bird Distribution Committee 2012). Most will move southeast, then south following grasslands (Schmutz and Fyfe 1987) to wintering locations in Texas and northern Mexico (Bechard and Schmutz 1995). Although historical records (Saunders 1921) indicate Ferruginous Hawks did overwinter in the state around the turn of the 19th century, it is not believed they currently do so. Birds from the western subpopulation apparently migrate into extreme western Montana from eastern Washington and Oregon, although only a handful of records exist and there are only three documented overwintering occurrences (see Distribution). Ferruginous Hawks begin arriving in southeastern Montana in mid- to late March (Wittenhagen 1992). Restani (1991) reported most returns to the Centennial Valley occurring in April and May. Most spring observations in the Montana Bird Distribution (2012) database are in April and May as well.

The habitat of Ferruginous Hawks in Montana has been studied extensively (Ensign 1983, Restani 1989, 1991, De Velice 1990, Wittenhagen 1992, Black 1992, Atkinson 1992, 1993) and described as mixed-grass prairie, shrub-grasslands, grasslands, grass-sagebrush complex, and sagebrush steppe. In southeastern Montana, Ensign (1983) reported mixed-grass prairie with black greasewood (Sarcobatus vermiculatus) and big sagebrush (Artemisia tridentata) in uplands and drainages. Other shrub and tree species present in the habitat were junipers (Juniperus ssp.), cottonwoods (Populus ssp), willows (Salix spp.), and ponderosa pine (Pinus ponderosa). Also in southeastern Montana, Wittenhagen (1992) reported Ferruginous Hawk habitat to consist of shrub-grasslands with big sagebrush present as well as wheatgrasses. The Kevin Rim area of north-central Montana has been categorized as grasslands dominated by bluebunch and western wheatgrass, blue gramma, and other grasses (De Velice 1990). Habitat also exists for Ferruginous Hawks in the Centennial Valley in the southwestern portion of the state. Restani (1989, 1991) reported grass-sagebrush complexes on mid-elevation slopes to be where most hawks nested. These complexes included sagebrush species and rabbitbrush as overstory to wheatgrasses, needle-and-thread grass, and junegrass. Also in southwestern Montana, Atkinson (1992, 1993) described the preferred habitat as sagebrush steppe over foothill prairie or mountain mahogany. Black (1992) surveyed Ferruginous Hawk habitat in Phillips County and reported the habitat to be 69% grassland, 25% shrubland and 13% bare area.

Nest location studies have also described the habitat Ferruginous Hawks use during the breeding season. 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 cultivated areas (20 percent) in north-central Montana, nests closer to cultivated fields and roads were more successful, presumably because of higher prey densities associated with edge habitats (Zelenak et al. 1997). 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). The average height of ground nests below the highest surrounding topographic feature was 10 meters, whereas the 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).

Ferruginous Hawks do not appear to nest in areas converted to agriculture (Schmutz 1984, Jasikoff 1982). A study done in Petroleum and Fergus counties seems to support this statement. Rogers and Rogers (1995) reported direct observations of Ferruginous Hawks avoiding crested wheatgrass (Agropyron cristatum) fields as nesting locations. They concluded few prey resources in such monotypic croplands as the reason for not nesting in these habitats.

In southeastern Montana White-tailed Jack Rabbits represent the greatest frequency (24.4%) and biomass of prey items, followed by Western Meadowlarks (18.3%), Thirteen-lined Ground Squirrels (12.7%), and Northern Pocket Gophers (11.7%) (Ensign 1983). In southwestern Montana (Restani 1991, Atkinson 1992) ground squirrels (S. armatus or S. elegans) were the most frequent food item (45 to 62%); other items greater than 10% included passerines, grasshoppers, and voles. Some studies in other areas of the species' range focused on vulnerability of prey. It is an important factor in habitat suitability, such that Ferruginous Hawks avoid dense vegetation that reduces their ability to see prey (Howard and Wolfe 1976, Wakeley 1978, Schmutz 1987). Prey vulnerability decreases where taller small-grain crops replace shorter grasses (Houston and Bechard 1984). Intensive agricultural practices, such as annual plowing and biennial fallowing, exclude many prey species (Wakeley 1978, Houston and Bechard 1984). In Alberta, prey abundance increases as the area of cultivation increases up to 30 percent, but abundance is reduced where agriculture is extensive, e.g., more than 30 percent (Schmutz 1989).

In southeastern Montana, predation and sibling fratricide were the major causes of nestling mortality, accounting for 34 and 27%, respectively, of total progeny loss (Ensign 1983). Territories often contain alternate nests (Atkinson 1992). Distribution appears clumped, with large areas of apparently suitable habitat unoccupied (Atkinson 1992). Ecological information relating to home ranges of Ferruginous Hawks comes from studies throughout the west including Washington, Utah, and Idaho. Density varies with cycles of prey abundance and home ranges average between 3.14 km to 90.3 km.

Most reproduction studies in Montana have been done in four areas in the state: the southeastern, the southwestern, the Kevin Rim area in north-central Montana, and Phillips County. Ferruginous Hawks arrive in Montana in mid- to late March (Wittenhagen 1992). Ensign (1983) reported hawks already present when the field season began in early April. Wittenhagen (1992) recorded eggs being laid in mid-April. Ensign (1983) mentions eggs present by the third week of April in 1981 and the end of April in 1982. The average clutch size for Ferruginous Hawk nests in Montana ranges between 2.57 and 3.37 (Ensign 1983, Wittenhagen 1992). Ferruginous Hawk eggs hatch in late May (Wittenhagen 1992) and the first week of June (Ensign 1983). Fledging occurred in late June to mid-July and juvenile birds were observed into late August (Ensign 1983, Wittenhagen 1992). The average number of young fledged from four studies in the state ranges from 1.07 to 3.50 (Ensign 1983, Meyers 1987, Restani 1989, Wittenhagen 1992), with higher fledging success in the southwestern part of the state; more tree nesting and therefore fewer ground predators (Wittenhagen 1992). Once young birds have fledged, they have low mortality rates. Zelenak et al. (1997), working in the Kevin Rim region, reported an 86% percent survival rate of juvenile birds from fledging to 60 days later. No evidence exists for year-old birds breeding, but 2 year-olds do regularly (Bechard and Schmutz 1995).

The Kevin Rim area in north-central Montana supports a very dense population of breeding Ferruginous Hawks. DuBois (1988) reported 24 breeding pairs in an area of 23.5 square km, which translates to almost 60 pairs per 100 square mile. Black (1992) reports a likely population of 260 individuals in Phillips County, based on the number of hawk observations over a certain survey size. Meyers (1987), working in the Dillon area in southwestern Montana, documented one the densest Ferruginous Hawk populations in the state with 58 (1985) and 69 (1986) occupied territories in only 417 square miles.

In 1991, the Ferruginous Hawk was petitioned for listing under the Endangered Species Act (Ure et al. 1991). This petition was rejected due to insufficient data to warrant listing (USFWS 1992). Ferruginous Hawks are not currently federally listed as a candidate or proposed species. The BLM in Montana identifies them as a sensitive species. Although no active management is currently in place for Ferruginous Hawks in Montana, other management plans do take this species into account. For example, Black-tailed Prairie Dog towns in the Judith-Valley-Phillips Resource Management Area are currently managed to help provide habitat for Ferruginous Hawks (Grensten 2002) as they use the dog towns for food and shelter. Ferruginous Hawks seem to accept and readily use artificial nest structures when placed in areas where populations have declined or where habitats lack suitable nest sites (Olendorff 1993). This practice would likely benefit Ferruginous Hawks in eastern Montana where nesting is primarily on the ground and nest structures would reduce predation (Wittenhagen 1992).