Ferruginous Hawk
Encyclopedia
The Ferruginous Hawk Buteo regalis (Latin, royal hawk), is a large bird of prey
. It is not a true hawk
like sparrowhawks or goshawks, but rather belongs to the broad-winged buteo hawks
, known as "buzzard
s" in Europe
. An old colloquial name is "Ferrugineous Rough-leg", due to its similarity to the closely related Rough-legged Hawk (B. lagopus).
This species
is a large, broad-winged hawk of the open, arid grassland
s, prairie
and shrub steppe
country; it is endemic to the interior parts of North America
. It is used as a falconry
bird in its native range.
This is the largest of the Buteo
s and is often mistaken for an eagle
due to its size, proportions, and behavior. As with all birds of prey, the female is larger than the male, but there is some overlap between small females and large males in the range of measurements. Length ranges from 20 to 27 in (50.8 to 68.6 cm) with an average of 23 inches (58.4 cm), wingspan from 48 to 60 in (121.9 to 152.4 cm) with an average of 56 inches (142.2 cm), and weight from 2.1 to 5 lb (952.5 to 2,268 g).
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:
There are no subspecies
.
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
(B. jamaicensis).
with dark legs. The back and wing
s are a brownish rust color. The head is white with a dark streak extending behind the eye
. The wing tips 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 (pinions) 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. 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. Dark "comma"-shaped markings are prominent at the wrist
s. The Ferruginous Hawk is one of the only two hawks that have feathers that cover their legs down to their toes, like the Golden Eagle. The other is the Rough-legged Hawk.
In flight, these birds soar with their wings in a dihedral.
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, sage
, and other arid shrub country. Nesting occurs in the open areas or in trees including cottonwoods, willow
s, and swamp oak
s 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 percent 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, knolls, 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 than necessary, suggesting that the distance is not fixed. The "nearest neighbor" distance has varied from less than 1 miles (1.6 km) to as much as 4 miles (6.4 km) with an average of 2 miles (3.2 km). 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 four to 2,450 square miles (10.4 to 6,346 square km). In Alberta, on one study site, there was a stable density of one pair per four square miles (10.4 square km), 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 two square miles (5.2 square km).
Territorial conflicts have been reported with other species, such as the Great Horned
and Short-eared Owl
, Northern Harrier, Red-tailed and Swainson's Hawk
s, Golden Eagle
, accipiter
s, raven
s, and magpies. It seems to be quite tolerant of conspecifics from adjacent territories.
s, and some insects. Mammal
s generally comprise 80 to 90 percent of the prey items or biomass in the diet with birds being the next most common mass component. The diet varies somewhat geographically, depending upon the distribution of prey species, but where the range of the Ferruginous Hawk overlaps, the black-tailed jackrabbit
is a major food species along with ground squirrel
s and pocket gopher
s. Depending upon the relative abundance of jackrabbits and ground squirrels, the latter could become the major food source. The white-tailed jackrabbit
are occasionally prey and weigh about twice as much as a Ferruginous Hawk. Common prey items are:
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:
In its "strike, kill, and consume" type of predation, the prey is seized with the feet and a series of blows may be meted out, including driving the rear talon into the body to puncture vital organs. Biting with the beak
may also take place. Before bringing prey to the nest, the adults will often eat the head. At the nest, birds are plucked and mammal
s torn into pieces before being fed to the young. Food caching has been noted, but not generally near the nest.
-laying period varies with latitude
, weather
, and possibly food
supply. In the Canadian parts of the range, laying occurs from the latter part of April through late June, whereas farther south laying occurs from about March 20 through mid May. The earliest recorded clutch was in January in Utah and laying could occur as late as July 3 in Canada. Egg-laying occurs at two-day intervals with incubation starting when the first egg is laid. Incubation
is shared by both sexes with each taking approximately the same number of shifts during the 32 day average incubation period. Replacement clutches following failure appears to be rare.
Courtship flights seem to be limited in the accepted sense. Both sexes engage in high, circling flight but literature details are sketchy. Soaring activities may primarily be variations on territorial defense flights as opposed to courtship per se. The "flutter-glide" flight consists of a series of shallow, rapid wing beats interspersed with brief glides and may serve to advertise the territory. The "sky-dance" is stimulated by an intruder and consists of slow flight with deep, labored wing beats with irregular yawing and pitching that may terminate in steep dives. In the "follow-soar" maneuver, the male Ferruginous Hawk will fly below an intruder and escort it out of the territory.
High perching occurs from prominent places around the nest, particularly early in the breeding cycle. Aggressive actions such as attacking, talon-grasping, and pursuit have been noted by some observers. Copulation begins before construction of the new nest, and increases in frequency until the start of egg laying. The passing of food may occur before the activity. The duration of copulation is from four to 18 seconds.
The Ferruginous Hawk is one of the most adaptable nesters of the raptors, and will use tree
s, ledges, rock
or dirt outcrops, the ground
, hay
stacks, nest platforms, power poles, and other man-made structures. Within some broad categories such as cliffs, the variety includes clay, dirt and rock substrates. Tree nests are typically in isolated trees or isolated clumps of trees in exposed locations. Authors differ as to whether ground nests are more successful than tree nests, but they are more susceptible to mammalian predation. Nest locations are reused frequently, but several nests may be built in an area. Typically, one or two alternate nests may exist but up to eight have been found on some territories.
The nests are made of ground debris such as sticks, branches, and cattails. Old nests will be refurbished, or nests of other species may be taken over and refurbished with sticks being added on top of the old nests. Odd items such as paper, rubbish, barbed wire
, cornstalks, plastic
and steel
cable have been incorporated into nests. Bark from trees and shrubs will be used for lining along with grasses and cow dung. Bits and pieces of greenery are often added to the nest. Prior to the removal of the bison
from this bird's range, nesting material often included bison bones, fur and dung. Both sexes are involved with building the nests and bringing materials, but the male seems to be more involved in retrieving materials while the female arranges them in the structure.
Clutch size varies from one to eight and is likely linked to food supply. The average clutch is three to four eggs, each 2.5 inches (6.4 cm) long and 2 inches (5.1 cm) wide. They are smooth, non-glossy and whitish in color, irregularly spotted or speckled and blotched with reddish-brown markings. There may be a concentration of darker pigments at the small end of the egg. Occasionally, the eggs are almost unmarked or have faint scribblings on them.
The nestling period varies from 38 to 50 days with brooding primarily by the female. Males fledge at 38 to 40 days and the females as late as 50 days after hatching, or 10 days later than their male siblings as they take longer to develop. Nestlings lie or sit for the first two weeks, stand at about three weeks and walk soon after. By 16 or 18 days, they are able to feed on their own. Wing flapping starts about day 23 and by day 33 the young are capable of vigorous flapping and "flap jumps." The nestlings are sensitive to high temperature
s and seek shade however possible in the nest.
Initial movement out of the nest is felt to be a response to heat stress as the young quickly move towards shade. The initial flight for the males is taken at 38 to 40 days while the slower-developing females fly about 10 days later. Post-fledging dependency upon the parents may last for several weeks. During the first four weeks after fledging, the young patrol increasingly large areas around the nest as they learn to hunt. Young hawks have killed prey as early as four days after fledging.
The Ferruginous Hawk is single-brooded, and as in so many raptors, the number of young reared is tied closely to food supply. In areas where jackrabbit populations are the principal food source, the initial clutch sizes and the number of reared young vary closely with variations in the number of jackrabbits. Fifty percent loss of young has been reported in low jackrabbit years. Fledging rates of 2.7 to 3.6 young per nest have been reported during years of abundant food supply. The high potential clutch size allows for a quick response to increases in the prey base.
Birds have been known to live for 20 years in the wild, but most birds probably die within the first five years. The oldest banded birds were recovered at age 20. First-year mortality has been estimated at 66 percent and the adult mortality at 25 percent. The reasons for mortality include illegal shooting, loss of a satisfactory food supply, harassment, predation, and starvation
of nestlings during times of low food supply. Ground nests are susceptible to predation by coyotes, and nestlings may be preyed upon by Great Horned Owl
s and Golden Eagle
s.
At times the Ferruginous Hawk has been considered threatened, endangered, or of concern on various threatened species lists but recent population
increases in local areas, coupled with conservation
initiatives, have created some optimism about the bird's future. It was formerly classified as a Near Threatened
species by the IUCN, but new research has confirmed that the Ferrugineous Hawk is common and widespread again. Consequently, it was downlisted to Least Concern
status in 2008.
Declines are mostly due to loss of quality habitat. Although flexible in choosing a nest site and exhibiting a high reproductive potential, this bird's restriction to natural grasslands on the breeding grounds and specialized predation on mammals persecuted on rangelands may make conservation a continuous concern. Historically, the birds entirely disappeared from areas where agriculture displaced the natural flora and fauna; for example it was noted in 1916 that the species was "practically extinct" in San Mateo County, California
. Studies have found that prairie dog
s can be a main prey item for Ferruginous Hawks, linking them to the populations of prairie dog towns in the mid-west and southwestern United States, which have been declining in recent years. This bird may also be sensitive to the use of pesticide
s on farms; they are also frequently shot. Threats to the overall population include:
The Ferruginous Hawk was on the National Audubon Society
's "Blue List" of species felt to be declining. From 1971 to 1981 it retained its "blue" status, and from 1982 to 1986 it was listed as a species of "Special Concern." The United States Fish and Wildlife Service placed it in a category of "undetermined" in 1973, and various states have placed it in categories of "Threatened" or "Endangered." In Canada
, the Committee on the Status of Endangered Wildlife in Canada considered this species "Threatened" in 1980.
Across the Canadian prairies, the range was diminishing up until 1980, and at that time, birds were felt to be occupying 48 percent of its original range. Numbers were generally felt to be diminishing and a total Canadian population was estimated at 500 to 1000 pairs. By 1987, population increases were being noted, and the Alberta population alone was estimated at 1,800 pairs. The upswing was likely due to a greater availability of food on the wintering grounds, making the birds more likely to breed when they returned to Canada. In the United States, there has been a history of concern for this species in many states with declines noted, but in 1988, one study suggested that the population in California and locally elsewhere may have increased significantly. The wintering population north of Mexico was estimated at 5,500 birds in 1986. In 1984, the population estimate for North America was between 3,000 and 4,000 pairs, and in 1987, it was 14,000 individuals.
Toxic chemicals have not been suggested as a significant threat to the Ferruginous Hawk. Management strategies must include the retention or reclamation of native grasslands for breeding as well as on the wintering grounds. Maintenance of high populations of prey species in wintering areas seems critical to the hawks' abilities to move onto the summer range in breeding condition. The integration of agricultural practices and policies into the management strategies is a crucial component of any overall scheme for conservation. The provision of nesting platforms has had positive effects and should be a part of local strategies. Public education and the elimination of persecution and human disturbance must be an important part of the overall conservation program.
Bird of prey
Birds of prey are birds that hunt for food primarily on the wing, using their keen senses, especially vision. They are defined as birds that primarily hunt vertebrates, including other birds. Their talons and beaks tend to be relatively large, powerful and adapted for tearing and/or piercing flesh....
. It is not a true hawk
Accipiter
The genus Accipiter is a group of birds of prey in the family Accipitridae, many of which are named as goshawks and sparrowhawks. They can be anatomically distinguished from their relatives by the lack of a procoracoid foramen. Two small and aberrant species usually placed here do possess a large...
like sparrowhawks or goshawks, but rather belongs to the broad-winged buteo hawks
Buteo
Buteo is a genus of medium to fairly large, wide-ranging raptors with a robust body and broad wings. In the Old World, members of this genus are called "buzzards", but "hawk" is used in North America...
, known as "buzzard
Buzzard
A buzzard is one of several large birds, but there are a number of meanings as detailed below.-Old World:In the Old World Buzzard can mean:* One of several medium-sized, wide-ranging raptors with a robust body and broad wings....
s" in Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
. An old colloquial name is "Ferrugineous Rough-leg", due to its similarity to the closely related Rough-legged Hawk (B. lagopus).
This species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
is a large, broad-winged hawk of the open, arid grassland
Grassland
Grasslands are areas where the vegetation is dominated by grasses and other herbaceous plants . However, sedge and rush families can also be found. Grasslands occur naturally on all continents except Antarctica...
s, prairie
Prairie
Prairies are considered part of the temperate grasslands, savannas, and shrublands biome by ecologists, based on similar temperate climates, moderate rainfall, and grasses, herbs, and shrubs, rather than trees, as the dominant vegetation type...
and shrub steppe
Steppe
In physical geography, steppe is an ecoregion, in the montane grasslands and shrublands and temperate grasslands, savannas, and shrublands biomes, characterized by grassland plains without trees apart from those near rivers and lakes...
country; it is endemic to the interior parts of North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
. It is used as a falconry
Falconry
Falconry is "the taking of wild quarry in its natural state and habitat by means of a trained raptor". There are two traditional terms used to describe a person involved in falconry: a falconer flies a falcon; an austringer flies a hawk or an eagle...
bird in its native range.
Description
Buteo
Buteo is a genus of medium to fairly large, wide-ranging raptors with a robust body and broad wings. In the Old World, members of this genus are called "buzzards", but "hawk" is used in North America...
s and is often mistaken for an eagle
Eagle
Eagles are members of the bird family Accipitridae, and belong to several genera which are not necessarily closely related to each other. Most of the more than 60 species occur in Eurasia and Africa. Outside this area, just two species can be found in the United States and Canada, nine more in...
due to its size, proportions, and behavior. As with all birds of prey, the female is larger than the male, but there is some overlap between small females and large males in the range of measurements. Length ranges from 20 to 27 in (50.8 to 68.6 cm) with an average of 23 inches (58.4 cm), wingspan from 48 to 60 in (121.9 to 152.4 cm) with an average of 56 inches (142.2 cm), and weight from 2.1 to 5 lb (952.5 to 2,268 g).
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.
There are no subspecies
Subspecies
Subspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...
.
Voice
The voiceBird song
Bird vocalization includes both bird calls and bird songs. In non-technical use, bird songs are the bird sounds that are melodious to the human ear. In ornithology and birding, songs are distinguished by function from calls.-Definition:The distinction between songs and calls is based upon...
is not well-described in literature
Literature
Literature is the art of written works, and is not bound to published sources...
. Alarm calls consist of kree - a or ke - ah and harsh kaah, kaah calls, the latter resembling some vocalizations of the herring gull
American Herring Gull
The American Herring Gull or Smithsonian Gull is a large gull which breeds in North America. It is often treated as a subspecies of the European Herring Gull but is now regarded as a separate species by some authorities.Adults are white with gray back and wings, black wingtips with white spots,...
. One description referred to the "wavering" alarm call and "breathy" notes, while other authors describe screams similar to those of the Red-tailed Hawk
Red-tailed Hawk
The Red-tailed Hawk is a bird of prey, one of three species colloquially known in the United States as the "chickenhawk," though it rarely preys on standard sized chickens. It breeds throughout most of North America, from western Alaska and northern Canada to as far south as Panama and the West...
(B. jamaicensis).
Identification
The male and female have identical markings. The main difference is size, with the female being larger. Perched birds have a white breast and bodyBody
With regard to living things, a body is the physical body of an individual. "Body" often is used in connection with appearance, health issues and death...
with dark legs. The back and wing
Wing
A wing is an appendage with a surface that produces lift for flight or propulsion through the atmosphere, or through another gaseous or liquid fluid...
s are a brownish rust color. The head is white with a dark streak extending behind the eye
Eye
Eyes are organs that detect light and convert it into electro-chemical impulses in neurons. The simplest photoreceptors in conscious vision connect light to movement...
. The wing tips 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 (pinions) 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. 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. Dark "comma"-shaped markings are prominent at the wrist
Wrist
In human anatomy, the wrist is variously defined as 1) the carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand;...
s. The Ferruginous Hawk is one of the only two hawks that have feathers that cover their legs down to their toes, like the Golden Eagle. The other is the Rough-legged Hawk.
In flight, these birds soar with their wings in a dihedral.
Habitat
The preferred habitat for Ferruginous Hawks are the aridArid
A region is said to be arid when it is characterized by a severe lack of available water, to the extent of hindering or even preventing the growth and development of plant and animal life...
and semiarid grassland
Grassland
Grasslands are areas where the vegetation is dominated by grasses and other herbaceous plants . However, sedge and rush families can also be found. Grasslands occur naturally on all continents except Antarctica...
regions of North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
. 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, sage
Sagebrush
Sagebrush is a common name of a number of shrubby plant species in the genus Artemisia native to western North America;Or, the sagebrush steppe ecoregion, having one or more kinds of sagebrush, bunchgrasses and others;...
, and other arid shrub country. Nesting occurs in the open areas or in trees including cottonwoods, willow
Willow
Willows, sallows, and osiers form the genus Salix, around 400 species of deciduous trees and shrubs, found primarily on moist soils in cold and temperate regions of the Northern Hemisphere...
s, and swamp oak
Oak
An oak is a tree or shrub in the genus Quercus , of which about 600 species exist. "Oak" may also appear in the names of species in related genera, notably Lithocarpus...
s 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 percent 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, knolls, 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 than necessary, suggesting that the distance is not fixed. The "nearest neighbor" distance has varied from less than 1 miles (1.6 km) to as much as 4 miles (6.4 km) with an average of 2 miles (3.2 km). 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 four to 2,450 square miles (10.4 to 6,346 square km). In Alberta, on one study site, there was a stable density of one pair per four square miles (10.4 square km), 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 two square miles (5.2 square km).
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.Territorial conflicts have been reported with other species, such as the Great Horned
Great Horned Owl
The Great Horned Owl, , also known as the Tiger Owl, is a large owl native to the Americas. It is an adaptable bird with a vast range and is the most widely distributed true owl in the Americas.-Description:...
and Short-eared Owl
Short-eared Owl
The Short-eared Owl is a species of typical owl . In Scotland this species of owl is often referred to as a cataface, grass owl or short-horned hootlet. Owls belonging to genus Asio are known as the eared owls, as they have tufts of feathers resembling mammalian ears. These "ear" tufts may or may...
, Northern Harrier, Red-tailed and Swainson's Hawk
Swainson's Hawk
The Swainson's Hawk , is a large buteo hawk of the Falconiformes, sometimes separated in the Accipitriformes like its relatives. This species was named after William Swainson, a British naturalist...
s, Golden Eagle
Golden Eagle
The Golden Eagle is one of the best known birds of prey in the Northern Hemisphere. Like all eagles, it belongs to the family Accipitridae. Once widespread across the Holarctic, it has disappeared from many of the more heavily populated areas...
, accipiter
Accipiter
The genus Accipiter is a group of birds of prey in the family Accipitridae, many of which are named as goshawks and sparrowhawks. They can be anatomically distinguished from their relatives by the lack of a procoracoid foramen. Two small and aberrant species usually placed here do possess a large...
s, raven
Raven
Raven is the common name given to several larger-bodied members of the genus Corvus—but in Europe and North America the Common Raven is normally implied...
s, and magpies. It seems to be quite tolerant of conspecifics from adjacent territories.
Hunting and feeding
The Ferruginous Hawk primarily hunts small to medium-sized mammals but will also take birds, reptileReptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
s, and some insects. Mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s generally comprise 80 to 90 percent of the prey items or biomass in the diet with birds being the next most common mass component. The diet varies somewhat geographically, depending upon the distribution of prey species, but where the range of the Ferruginous Hawk overlaps, the black-tailed jackrabbit
Black-tailed Jackrabbit
The black-tailed jackrabbit , also known as the american desert hare, is a common hare of the western United States and Mexico, where it is found at elevations from sea level to up to...
is a major food species along with ground squirrel
Ground squirrel
The ground squirrels are members of the squirrel family of rodents which generally live on or in the ground, rather than trees. The term is most often used for the medium-sized ground squirrels, as the larger ones are more commonly known as marmots or prairie dogs, while the smaller and less...
s and pocket gopher
Pocket gopher
The pocket gophers are burrowing rodents of the family Geomyidae. These are the "true" gophers, though several ground squirrels of the family Sciuridae are often called gophers as well...
s. Depending upon the relative abundance of jackrabbits and ground squirrels, the latter could become the major food source. The white-tailed jackrabbit
White-tailed Jackrabbit
The White-tailed Jackrabbit , also known as the Prairie Hare and the White Jack, is a hare found in western North America. Briefly reputed to have been extirpated , it is now clear from observations, roadkilled specimens and historical records that white-tailed jackrabbits are still extant in...
are occasionally prey and weigh about twice as much as a Ferruginous Hawk. Common prey items are:
|
|
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 40 to 60 ft (12.2 to 18.3 m) 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 windWindWind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space...
s, 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 dogDogThe domestic dog is a domesticated form of the gray wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The dog may have been the first animal to be domesticated, and has been the most widely kept working, hunting, and companion animal in...
s, and to claim shot "dogs" by flying to them and mantling over them.
Beak
The beak, bill or rostrum is an external anatomical structure of birds which is used for eating and for grooming, manipulating objects, killing prey, fighting, probing for food, courtship and feeding young...
may also take place. Before bringing prey to the nest, the adults will often eat the head. At the nest, birds are plucked and mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s torn into pieces before being fed to the young. Food caching has been noted, but not generally near the nest.
Reproduction and life history
Copulation occurs during and after nest building. The eggEgg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
-laying period varies with latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
, weather
Weather
Weather is the state of the atmosphere, to the degree that it is hot or cold, wet or dry, calm or stormy, clear or cloudy. Most weather phenomena occur in the troposphere, just below the stratosphere. Weather refers, generally, to day-to-day temperature and precipitation activity, whereas climate...
, and possibly food
Food
Food is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals...
supply. In the Canadian parts of the range, laying occurs from the latter part of April through late June, whereas farther south laying occurs from about March 20 through mid May. The earliest recorded clutch was in January in Utah and laying could occur as late as July 3 in Canada. Egg-laying occurs at two-day intervals with incubation starting when the first egg is laid. Incubation
Avian incubation
Incubation refers to the process by which certain oviparous animals hatch their eggs, and to the development of the embryo within the egg. The most vital factor of incubation is the constant temperature required for its development over a specific period. Especially in domestic fowl, the act of...
is shared by both sexes with each taking approximately the same number of shifts during the 32 day average incubation period. Replacement clutches following failure appears to be rare.
Courtship flights seem to be limited in the accepted sense. Both sexes engage in high, circling flight but literature details are sketchy. Soaring activities may primarily be variations on territorial defense flights as opposed to courtship per se. The "flutter-glide" flight consists of a series of shallow, rapid wing beats interspersed with brief glides and may serve to advertise the territory. The "sky-dance" is stimulated by an intruder and consists of slow flight with deep, labored wing beats with irregular yawing and pitching that may terminate in steep dives. In the "follow-soar" maneuver, the male Ferruginous Hawk will fly below an intruder and escort it out of the territory.
High perching occurs from prominent places around the nest, particularly early in the breeding cycle. Aggressive actions such as attacking, talon-grasping, and pursuit have been noted by some observers. Copulation begins before construction of the new nest, and increases in frequency until the start of egg laying. The passing of food may occur before the activity. The duration of copulation is from four to 18 seconds.
Tree
A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to...
s, ledges, rock
Rock (geology)
In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...
or dirt outcrops, the ground
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
, hay
Hay
Hay is grass, legumes or other herbaceous plants that have been cut, dried, and stored for use as animal fodder, particularly for grazing livestock such as cattle, horses, goats, and sheep. Hay is also fed to pets such as rabbits and guinea pigs...
stacks, nest platforms, power poles, and other man-made structures. Within some broad categories such as cliffs, the variety includes clay, dirt and rock substrates. Tree nests are typically in isolated trees or isolated clumps of trees in exposed locations. Authors differ as to whether ground nests are more successful than tree nests, but they are more susceptible to mammalian predation. Nest locations are reused frequently, but several nests may be built in an area. Typically, one or two alternate nests may exist but up to eight have been found on some territories.
The nests are made of ground debris such as sticks, branches, and cattails. Old nests will be refurbished, or nests of other species may be taken over and refurbished with sticks being added on top of the old nests. Odd items such as paper, rubbish, barbed wire
Barbed wire
Barbed wire, also known as barb wire , is a type of fencing wire constructed with sharp edges or points arranged at intervals along the strand. It is used to construct inexpensive fences and is used atop walls surrounding secured property...
, cornstalks, plastic
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...
and steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
cable have been incorporated into nests. Bark from trees and shrubs will be used for lining along with grasses and cow dung. Bits and pieces of greenery are often added to the nest. Prior to the removal of the bison
American Bison
The American bison , also commonly known as the American buffalo, is a North American species of bison that once roamed the grasslands of North America in massive herds...
from this bird's range, nesting material often included bison bones, fur and dung. Both sexes are involved with building the nests and bringing materials, but the male seems to be more involved in retrieving materials while the female arranges them in the structure.
The nestling period varies from 38 to 50 days with brooding primarily by the female. Males fledge at 38 to 40 days and the females as late as 50 days after hatching, or 10 days later than their male siblings as they take longer to develop. Nestlings lie or sit for the first two weeks, stand at about three weeks and walk soon after. By 16 or 18 days, they are able to feed on their own. Wing flapping starts about day 23 and by day 33 the young are capable of vigorous flapping and "flap jumps." The nestlings are sensitive to high temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
s and seek shade however possible in the nest.
The Ferruginous Hawk is single-brooded, and as in so many raptors, the number of young reared is tied closely to food supply. In areas where jackrabbit populations are the principal food source, the initial clutch sizes and the number of reared young vary closely with variations in the number of jackrabbits. Fifty percent loss of young has been reported in low jackrabbit years. Fledging rates of 2.7 to 3.6 young per nest have been reported during years of abundant food supply. The high potential clutch size allows for a quick response to increases in the prey base.
Birds have been known to live for 20 years in the wild, but most birds probably die within the first five years. The oldest banded birds were recovered at age 20. First-year mortality has been estimated at 66 percent and the adult mortality at 25 percent. The reasons for mortality include illegal shooting, loss of a satisfactory food supply, harassment, predation, and starvation
Starvation
Starvation is a severe deficiency in caloric energy, nutrient and vitamin intake. It is the most extreme form of malnutrition. In humans, prolonged starvation can cause permanent organ damage and eventually, death...
of nestlings during times of low food supply. Ground nests are susceptible to predation by coyotes, and nestlings may be preyed upon by Great Horned Owl
Great Horned Owl
The Great Horned Owl, , also known as the Tiger Owl, is a large owl native to the Americas. It is an adaptable bird with a vast range and is the most widely distributed true owl in the Americas.-Description:...
s and Golden Eagle
Golden Eagle
The Golden Eagle is one of the best known birds of prey in the Northern Hemisphere. Like all eagles, it belongs to the family Accipitridae. Once widespread across the Holarctic, it has disappeared from many of the more heavily populated areas...
s.
Status and conservation
Population
A population is all the organisms that both belong to the same group or species and live in the same geographical area. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals...
increases in local areas, coupled with conservation
Conservation biology
Conservation biology is the scientific study of the nature and status of Earth's biodiversity with the aim of protecting species, their habitats, and ecosystems from excessive rates of extinction...
initiatives, have created some optimism about the bird's future. It was formerly classified as a Near Threatened
Near Threatened
Near Threatened is a conservation status assigned to species or lower taxa that may be considered threatened with extinction in the near future, although it does not currently qualify for the threatened status...
species by the IUCN, but new research has confirmed that the Ferrugineous Hawk is common and widespread again. Consequently, it was downlisted to Least Concern
Least Concern
Least Concern is an IUCN category assigned to extant taxon or lower taxa which have been evaluated but do not qualify for any other category. As such they do not qualify as threatened, Near Threatened, or Conservation Dependent...
status in 2008.
Declines are mostly due to loss of quality habitat. Although flexible in choosing a nest site and exhibiting a high reproductive potential, this bird's restriction to natural grasslands on the breeding grounds and specialized predation on mammals persecuted on rangelands may make conservation a continuous concern. Historically, the birds entirely disappeared from areas where agriculture displaced the natural flora and fauna; for example it was noted in 1916 that the species was "practically extinct" in San Mateo County, California
San Mateo County, California
San Mateo County is a county located in the San Francisco Bay Area of the U.S. state of California. It covers most of the San Francisco Peninsula just south of San Francisco, and north of Santa Clara County. San Francisco International Airport is located at the northern end of the county, and...
. Studies have found that prairie dog
Prairie dog
Prairie dogs are burrowing rodents native to the grasslands of North America. There are five different species of prairie dogs: black-tailed, white-tailed, Gunnison's, Utah and Mexican prairie dogs. They are a type of ground squirrel, found in the United States, Canada and Mexico...
s can be a main prey item for Ferruginous Hawks, linking them to the populations of prairie dog towns in the mid-west and southwestern United States, which have been declining in recent years. This bird may also be sensitive to the use of pesticide
Pesticide
Pesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical unicycle, biological agent , antimicrobial, disinfectant or device used against any pest...
s on farms; they are also frequently shot. Threats to the overall population include:
- cultivation of native prairie grassland and subsequent habitat loss
- tree invasion of northern grassland habitats
- reductions in food supply due to agricultural pest management programs
- shooting and human interference
The Ferruginous Hawk was on the National Audubon Society
National Audubon Society
The National Audubon Society is an American non-profit environmental organization dedicated to conservation. Incorporated in 1905, Audubon is one of the oldest of such organizations in the world and uses science, education and grassroots advocacy to advance its conservation mission...
's "Blue List" of species felt to be declining. From 1971 to 1981 it retained its "blue" status, and from 1982 to 1986 it was listed as a species of "Special Concern." The United States Fish and Wildlife Service placed it in a category of "undetermined" in 1973, and various states have placed it in categories of "Threatened" or "Endangered." In Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, the Committee on the Status of Endangered Wildlife in Canada considered this species "Threatened" in 1980.
Across the Canadian prairies, the range was diminishing up until 1980, and at that time, birds were felt to be occupying 48 percent of its original range. Numbers were generally felt to be diminishing and a total Canadian population was estimated at 500 to 1000 pairs. By 1987, population increases were being noted, and the Alberta population alone was estimated at 1,800 pairs. The upswing was likely due to a greater availability of food on the wintering grounds, making the birds more likely to breed when they returned to Canada. In the United States, there has been a history of concern for this species in many states with declines noted, but in 1988, one study suggested that the population in California and locally elsewhere may have increased significantly. The wintering population north of Mexico was estimated at 5,500 birds in 1986. In 1984, the population estimate for North America was between 3,000 and 4,000 pairs, and in 1987, it was 14,000 individuals.
Toxic chemicals have not been suggested as a significant threat to the Ferruginous Hawk. Management strategies must include the retention or reclamation of native grasslands for breeding as well as on the wintering grounds. Maintenance of high populations of prey species in wintering areas seems critical to the hawks' abilities to move onto the summer range in breeding condition. The integration of agricultural practices and policies into the management strategies is a crucial component of any overall scheme for conservation. The provision of nesting platforms has had positive effects and should be a part of local strategies. Public education and the elimination of persecution and human disturbance must be an important part of the overall conservation program.
External links
- Ferruginous Hawk - Buteo regalis USGS Patuxent Bird Identification InfoCenter
- Ferruginous Hawk Species Account - Cornell Lab of Ornithology
- Ferruginous Hawk Information and Photos - South Dakota Birds and Birding
- ferruginoushawk.org - ferruginoushawk.org
- Several Closeups of the Ferruginous Hawk
- Ferruginous Hawk videos on the Internet Bird Collection
- Ferruginous Hawk photo gallery VIREO