Ferruginous hawk
The ferruginous hawk is a large bird of prey and belongs to the broad-winged buteo hawks. An old colloquial name is ferrugineous rough-leg, due to its similarity to the closely related rough-legged hawk.
The generic name buteo is Latin for 'buzzard'. The specific epithet regalis is Latin for 'royal'. The common name 'ferruginous' means 'rust-colored' or 'reddish-brown'.
This species is a large, broad-winged hawk of the open, arid grasslands, prairie and bush steppe country; it is endemic to the interior parts of North America. It is used as a falconry bird in its native ranges.
Description
This is the largest of the North American Buteos and is often mistaken for an eagle due to its size, proportions, and behavior. Among all the nearly thirty species of Buteo in the world, only the upland buzzard of Asia averages larger in length and wingspan. The weight of the upland buzzard and ferruginous broadly overlaps and which of these two species is the heaviest in the genus is debatable. As with all birds of prey, the female ferruginous hawk is larger than the male, but there is some overlap between small females and large males in the range of measurements. Length in this species ranges from with an average of, wingspan from, with an average of about, and weight from. Weight varies in the species relatively restricted breeding range. In the southern reaches of the species breeding range, i.e. Arizona, New Mexico and Utah, males average, in a sample of fifteen, and females average, in a sample of four. In the northern stretches of the breeding range, in southern Canada, Washington, Idaho and North Dakota, the hawks are heavier averaging in males and in females. Upland buzzard average weights were intermediate between those body mass surveys, notably heavier than the first and less heavier than the latter one, particularly the sample of 37 ferruginous hawk females place it as the most massive type of Buteo in northern populations.Adults have long broad wings and a broad gray, rusty, or white tail. The legs are feathered to the talons, like the rough-legged hawk. There are two color forms:
- Light morph birds are rusty brown on the upper parts and pale on the head, neck, and underparts with rust on the legs and some rust marking on the underwing. The upper wings are grey. The "ferruginous" name refers to the rusty color of the light-morph birds.
- Dark-morph birds are dark brown on both upperparts and underparts with light areas on the upper and lower wings.
Voice
The voice is not well-described in literature. Alarm calls consist of kree – a or ke – ah and harsh kaah, kaah calls, the latter resembling some vocalizations of the herring gull. One description referred to the "wavering" alarm call and "breathy" notes, while other authors describe screams similar to those of the red-tailed hawk.Identification
The male and female have identical markings. The main difference is size, with the female being somewhat larger. Perched birds have a white breast and body with dark legs. The back and wings are a brownish rust color. The head is white with a dark streak extending behind the eye. The wingtips almost reach the tip of the tail.The underside is primarily light colored with the dark legs forming a "V" shape. The reddish upper-back color extends to the inner wing-coverts or "shoulders." The primary remiges are dark gray with conspicuous light "windows" in the inner primaries. Three prominent light areas on the upper surface stand out as two "windows" on the outer wings and a rufous rump mark, perhaps the most significant feature of a flying ferruginous hawk. The underwings are whitish overall with rufous markings, particularly in the patagial area. This gives a smudgy appearance to the wings, but less dark than in a red-tailed hawk. The ferruginous hawk is noticeably longer winged than a red-tailed hawk, although the wings appear slenderer than the latter species the total wing area of the ferruginous is considerably more. However, red-tailed hawks can be nearly as bulky and heavy. Dark "comma"-shaped markings are prominent at the wrists. The ferruginous hawk is one of only two hawks that have feathers that cover their legs down to their toes, like the golden eagle. The other is the rough-legged buzzard. The pale morph of the closely related but more slender rough-legged species is best distinguished by its darker coloration, with a broad black tail band and a dark band across the chest. The dark morph Rough-leg is more a slaty coloration than the more brownish dark morph ferruginous. Swainson's hawks and especially rough-legged buzzards can be nearly as long-winged but are less bulky and heavily built than the ferruginous. Among the normal standard measurements, the wing chord measures, the tarsus measures and the tail measures. Additionally, the grasp is and the third toe, indicating that the ferruginous hawks has the largest and most robust feet of any of the world's Buteos. Compared to other Buteos, the ferruginous has a larger bill, at, with a much wider gap when the bill is opened, at.
In-flight, these birds soar with their wings in a dihedral.
Habitat
The preferred habitat for ferruginous hawks are the arid and semiarid grassland regions of North America. The countryside is open, level, or rolling prairies; foothills or middle elevation plateaus largely devoid of trees; and cultivated shelterbelts or riparian corridors. Rock outcrops, shallow canyons, and gullies may characterize some habitats. These hawks avoid high elevations, forest interiors, narrow canyons, and cliff areas.During the breeding season, the preference is for grasslands, sagebrush, and other arid shrub country. Nesting occurs in the open areas or in trees including cottonwoods, willows, and swamp oaks along waterways. Cultivated fields and modified grasslands are avoided during the breeding period. The density of ferruginous hawks in grasslands declines in an inverse relationship to the degree of cultivation of the grasslands. However, high densities have been reported in areas where nearly 80% of the grassland was under cultivation.
The winter habitat is similar to that used during the summer. However, cultivated areas are not necessarily avoided, particularly when the crops are not plowed under after harvest. The standing stubble provides habitat for the small-mammal prey base needed by ferruginous and other hawks. One requisite of the habitat is perches such as poles, lone trees, fence posts, hills, rocky outcrops or large boulders. Ferruginous hawks nest in trees if they are available, including riparian strips, but the presence of water does not appear to be critical to them.
The ferruginous hawk maintains minimum distances from other nesting raptors but will nest closer when necessary, suggesting that the distance is not fixed. The "nearest neighbor" distance has varied from less than to as much as with an average of. Nests facing different hunting territories are tolerated much closer than nests facing the same hunting territory. The minimum distance between nests is probably about one half mile on densely occupied areas. Nesting densities in several studies have varied from one pair per. In Alberta, on one study site, there was a stable density of one pair per, on average with little deviation from this mean. In Idaho, the average home range for four pairs of ferruginous hawk in the Snake River area was slightly over.
Behavior
The flight of the ferruginous hawk is active, with slow wing beats much like that of a small eagle. Soaring with the wings held in a strong dihedral has been noted, as well as gliding with the wings held flat, or in a modified dihedral. Hovering and low cruising over the ground are also used as hunting techniques. The wing beat has been described as "fluid" by some observers.Dietary biology
The ferruginous hawk primarily hunts small to medium-sized mammals but will also take birds, reptiles, and some insects. Mammals generally comprise 80–90% of the prey items or biomass in the diet with birds being the next most common mass component.Method of predation
These birds search for prey while flying over open country or from a perch. They may also wait in ambush outside the prey's burrow. Hunting may occur at any time of the day depending upon the activity patterns of the major prey species. A bimodal pattern of early morning and late afternoon hunting may be common. The hunting tactics can be grouped into seven basic strategies:- Perch and Wait – perching is on any elevated natural or man-made site
- Ground Perching – the hawk will stand on the ground at a rodent burrow after initially locating it from the air. As the burrowing animal reaches the surface, the hawk rises into the air and pounces upon it even while it is still underneath the loose earth.
- Low-level Flight – birds will course over the landscape within a few yards of the ground and pursue in direct, low-level chases, or they will hunt from above the ground.
- High-level Flight – birds will hunt while soaring, but the success rate is generally low.
- Hovering – using quickened wing beats, often in times of increased winds, the birds will search the ground and drop on the prey.
- Cooperative Hunting – mates have been known to assist each other.
- Piracy – the ferruginous hawk has been observed gathering around a hunter shooting prairie dogs, and claiming shot "dogs" by flying to them and mantling over them.