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Overview

Brief Summary

Raptors, or birds of prey, hunt mammals, reptiles, fish and other birds. They grab their prey in flight, either in the air, from the ground or out of the water. That is why they have sharp claws, called talons. In order to rip their victim apart, they also have a strong hooked bill. Raptors have very keen eyesight and therefore usually hunt during the day. Peregrines are an exception, hunting often at dusk.
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Comprehensive Description

The family Accipitridae encompasses many of the diurnal birds of prey, including the familiar hawks and eagles. It is one of the largest avian families, and the largest family in the order Falconiformes. The Howard and Moore Checklist of the Birds of the World recognizes 233 species in 67 genera in this family worldwide. Twenty-four of these species and 14 genera are native to North America. Many of the species in this family also include multiple subspecies. For example, up to 23 subspecies of the variable goshawk are recognized.

A great deal of diversity exists among the members of the Accipitridae. Members of this family span the globe, living in habitats as wide ranging as tundra, alpine meadows and rainforests. They eat fish, mammals, birds, bats, invertebrates, carrion and some fruit. They nest on cliffs, in trees or sometimes on the ground and lay between one and nine eggs. Physical size is also quite variable within this group, with wingspans ranging from 50 cm to 3 m.

  • 2003. E Dickinson, ed. The Howard and Moore Complete Checklist of the Birds of the World. London: Christopher Helm.
  • Kemp, A., I. Newton. 2003. Hawks, Eagles and Old World Vultures. Pp. 162-175 in C Perrins, ed. The New Encyclopedia of Birds. Oxford: Oxford University Press.
  • Snyder, H. 2001. Hawks and Allies. Pp. 212-224 in C Elphick, J Dunning, D Sibley, eds. The Sibley Guide to Bird Life & Behavior. New York: Alfred A. Knopf, Inc.
  • Thiollay, J. 1994. Family Accipitridae (hawks and eagles). Pp. 52-105 in J del Hoyo, A Elliott, J Sargatal, eds. Handbook of the Birds of the World. Vol. 2. New World Vultures to Guineafowl. Barcelona: Lynx Edicions.
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Distribution

Accipitrids are found world wide. They live on every continent except Antarctica, and on most oceanic islands. They inhabit every major habitat type except the northernmost arctic tundra and the driest deserts. The highest diversity of accipitrid species is found in tropical regions.

Biogeographic Regions: nearctic (Native ); palearctic (Native ); oriental (Native ); ethiopian (Native ); neotropical (Native ); australian (Native ); oceanic islands (Native )

Other Geographic Terms: holarctic ; cosmopolitan

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Physical Description

Morphology

Accipitrids are diurnal birds of prey with broad wings, hooked beaks, strong legs and feet and sharp talons. All accipitrids have a cere, which is a waxy membrane that is often brightly colored, and covers the base of the upper mandible. They have large eyes that are shaded by a supraorbital ridge in most species, making the face appear fierce. Adult Accipitrids have wingspans ranging from 50 to 300 cm and total body lengths ranging from 25 to 150 cm. The body masses of Accipitrids range from 80 g to 12.5 kg.

An assortment of body shapes and plumage can be seen among Accipitrids. For example, tails can be square, rounded, wedge-shaped or even forked. Accipitrid physical characteristics reflect adaptations to their habitat, mode of foraging and prey. For example, forest dwelling species generally have short wings and long tails, a combination which affords them maneuverability. Species that live in open habitats and hunt by soaring generally have long, broad wings and short tails, which allow them to soar easily over long distances. Many of the soaring species also have "fingers", which are long outer primary feathers that reduce drag on the wings and allow the birds to soar at slow speeds without stalling.

Accipitrids are colored to blend in with their environment, and are usually brown, black or gray with some streaking or barring. Many have paler underparts than upperparts and barred underwing and tail feathers, a patterning that may make them less visible to prey.  Several species of raptors show plumage polymorphism (light and dark morphs) or variation in plumage across their geographic range.

In most Accipitridae species, females are larger than males. This characteristic, called reversed sexual size dimorphism, is especially dramatic in bird-eating species. Though there is no consensus among scientists about why reversed sexual size dimorphism occurs, it is clearly more pronounced in species that hunt quick, agile prey. Some Accipitrids also show sexual dimorphism in plumage coloration. In species where this occurs, the male is usually more brightly colored than the female, and the female looks similar to the juveniles.

First-year accipitrid plumage is usually quite different from adult plumage, and very similar between species. Most juveniles have brown upperparts, sometimes mottled with light spots, and lighter underparts with brownish streaks. Juveniles also often have bigger (broader or longer) wing and tail feathers than adults, which may serve to make flying easier for the novice birds. After growing their first feathers, Accipitrids molt once per year. Many species develop adult plumage after the first year. In other species, including most eagles, the transformation from juvenile to adult plumage takes place over the course of several years, and the young bird passes through several sets of intermediate plumage.

Accipitrids share many traits with their falconid relatives, including strong beaks, feet and talons, and forward directed eyes. However, accipitrids are distinguished from falcons by their yellow, red or hazel, rather than brown eyes, nest building behavior (not exhibited in falcons), skeletal differences and forceful ejection of excreta.

Other Physical Features: endothermic ; bilateral symmetry ; polymorphic

Sexual Dimorphism: female larger; sexes colored or patterned differently; male more colorful

  • Sibley, C., J. Ahlquist. 1990. Phylogeny and Classification of Birds: A Study in Molecular Evolution. New Haven, Connecticut: Yale University Press.
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Ecology

Habitat

Accipitrids are found in most terrestrial habitats, including tundra, alpine meadows, grasslands, desserts, sea coasts, rainforests, woodlands, agricultural, suburban and even some urban areas. They are also found at most elevations, from coastal areas at sea level to the tops of mountains. The highest numbers of accipitrid species are found in forests and woodlands, whereas less productive habitats such as desert steppes and tundra can typically support only one or two species. Many raptor species rely on trees for nesting, perching, roosting and hunting. Therefore, habitats with trees can generally support many more raptor species than those without trees.

Accipitrids appear to select habitat based largely on food availability. A high quality accipitrid habitat is one with large quantities of high quality food that is accessible and predictable over time. Other characteristics that may be important in habitat selection are the frequency and intensity of human disturbance, risk of predation and availability of suitable nest sites, foraging perches and shelters.

Many Accipitrids migrate between breeding and wintering habitats. Individuals that migrate south for the winter usually choose a wintering habitat that is similar in structure to their breeding habitat. For example, species that breed in open woodlands generally choose wintering habitats in fairly open tropical forests.

Habitat Regions: temperate ; tropical ; terrestrial

Terrestrial Biomes: tundra ; taiga ; desert or dune ; savanna or grassland ; chaparral ; forest ; rainforest ; scrub forest ; mountains

Aquatic Biomes: coastal

Wetlands: marsh ; swamp ; bog

Other Habitat Features: urban ; suburban ; agricultural ; riparian ; estuarine

  • 2003. Hawks and Eagles (Accipitridae). Pp. 317-328 in A Evans, R Garrison, M Hutchins, eds. Grzimek's Animal Life Encyclopedia, Vol. 8. Detroit: Gale Group.
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Trophic Strategy

Members of the family Accipitridae are generally opportunistic predators that eat whatever prey is most abundant, accessible and easy to catch. Individual species may specialize on a certain group of prey, but most will also eat a wide variety of prey if it is available. Prey items include birds (adults, chicks and eggs), mammals (from bats to lambs), reptiles (including lizards and snakes), amphibians, fish, carrion and many different invertebrates. Though most Accipitrids are exclusively carnivorous, several species occasionally eat fruit, including the fruits of the oil palm (Elaeis guineensis), which is important in the diet of the palm-nut vulture.

Individual species of accipitrids do often specialize on specific groups of prey. For example, most buteos eat primarily small mammals and most accipiters prey on birds. The bat hawk specializes on bats, and the snail kite specializes on apple snails. Other species are generalist predators that eat a variety of prey. For example, the common black-hawk counts birds, fish, crayfish and aquatic insect larvae among its prey. Carrion is the main staple in the diet of some species, namely vultures, but is incidental in the diets of many other species. Animal and human excrement are also significant parts of the diets of a few species, including Egyptian vultures and hooded vultures.

Accipitrids use a range of hunting techniques, which depend on their prey, their habitat and their morphology. The most common method of hunting is perch-hunting. This method is the least energy-demanding and allows the hunter to detect inconspicuous prey, and to avoid being detected by their prey until they are descending upon it. Hovering and soaring are techniques employed by the large-winged Accipitrids that hunt in open habitats. Like perch hunting, this technique allows Accipitrids to detect inconspicuous prey. Slow soaring is also used by vultures, which use their excellent eyesight to locate carcasses and to watch other soaring vultures in case they have located a carcass. Still other species use ambush hunting, the technique of hiding quietly and ambushing prey as it passes by. Finally, active flight is a hunting technique used by many of the insectivorous species and the bat hawk. Many species use a behavior called "stooping" to surprise their prey. From very high, the bird folds its wings back and plummets toward the prey, opening it's wings and swinging its feet forward just before striking the prey. Vultures and eagles descending to prey can reach speeds of 90 km/hr or more.

A few species of accipitrids may use cryptic coloration to get close to their prey. For example, the plumage of zone-tailed hawks (Buteo albonotatus) looks similar to turkey vultures (Cathartes aura). By imitating turkey vultures both in plumage and in manner of flying, this hawk may be able to approach prey without being noticed by prey that are habituated to the harmless turkey vultures.

Most accipitrids hunt solitarily. However, cooperative hunting does occasionally occur in several buzzard and eagle species as well as some other accipitrid species. Generally, cooperation occurs between mated pairs or groups of related individuals. Cooperation generally increases hunting success rate and allows for the capture of larger prey than could be accomplished by a single individual. For example, groups of closely related Harris's hawks sometimes work together to flush jackrabbits from cover and catch them as they emerge. Working together, these birds catch more prey than they would be able to catch alone, and are often able to catch enough prey to satisfy the energetic requirements of the entire group.

Once they have captured prey, accipitrids kill their prey by repeatedly puncturing it with their talons. Prey are swallowed whole or ripped apart with the sharp, hooked beak. Indigestible materials like fur, feathers and insect exoskeletons, if swallowed, are regurgitated in a pellet. If a prey item is not consumed in entirety, it may be cached for later consumption, particularly during the breeding season.

Accipitrids (not in captivity) must ingest 10 to 25 percent of their body weight in prey each day. This amount varies with climate and body size. Larger species require a smaller proportion of their body weight. Consumption requirements increase in winter compared to summer and in temperate compared to tropical climates. Accipiters are almost never seen drinking. They presumably ingest sufficient water from their food.

Foraging Behavior: stores or caches food

Primary Diet: carnivore (Eats terrestrial vertebrates, Piscivore , Eats eggs, Insectivore , Eats non-insect arthropods, Molluscivore , Scavenger )

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Associations

Accipitrids impact populations of their prey at a local scale. For example, research has shown that predation by rough-legged buzzards is probably responsible for the 3- to 4-year population cycles of lemmings in the Arctic tundra. Predation pressure by accipitrids also influences the evolution of behavior, habitat selection, and life history of their prey species. Accipitrids are also host to a number of skin and feather mites, some of which are harmful and others of which are beneficial.

Accipitrids regularly use the activities of other species to improve their hunting efficiency. Insect- and snake-eaters follow troops of monkeys, catching the insects and tree snakes that the monkeys disturb. Some Accipitrids also engage in kleptoparasitism, stealing food from other raptors.

Nests built by accipitrids are regularly used by other bird species (including other accipitrids). For example, great horned owls, barred owls, and merlins all use the nests of accipitrid species.

Commensal/Parasitic Species:

  • feather and skin mites

  • Philips, J. 2000. A review and checklist of the parasitic mites (Acarina) of the Falconiformes and Strigiformes. Journal of Raptor Research, 34(3): 210-231.
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Accipitrid eggs and chicks are vulnerable to climbing and aerial predators. Parents, therefore, expend considerable effort protecting their offspring from predation. Parents actively defend a territory around the nest from conspecifics and potential predators. They may also attempt to camouflage the nest by decorating it with both live and dead vegetation.

Chicks exhibit behaviors to evade predation from a very early age. When they detect a predator, chicks either lay low in the nest and remain still, or lie on their backs and strike at the predator with their talons. As soon as they are able to leave the nest, chicks spend most of their time perched near the nest, rather than in it, which may make them less visible to predators.

Known Predators:

Anti-predator Adaptations: cryptic

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Animal / dung/debris feeder
clustered apothecium of Cheilymenia cadaverina feeds on dung/debris pellet of Accipitridae

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Known prey organisms

  • D. L. Pattie and N. A. M. Verbeek, Alpine birds of the Beartooth Mountains, Condor 68:167-176 (1966); Alpine mammals of the Beartooth Mountains, Northwest Sci. 41(3):110-117 (1967).
  • I. K. Sharma, A study of ecosystems of the Indian desert, Trans. Indian Soc. Desert Technol. and Univ. Center Desert Stud. 5(2):51-55, from p. 52 and A study of agro-ecosystems in the Indian desert, ibid. 5:77-82, from p. 79 1980).
  • Myers, P., R. Espinosa, C. S. Parr, T. Jones, G. S. Hammond, and T. A. Dewey. 2006. The Animal Diversity Web (online). Accessed February 16, 2011 at http://animaldiversity.org. http://www.animaldiversity.org
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Life History and Behavior

Behavior

Accipitrids use visual displays, often combined with vocalizations, to convey messages to one another. Many male accipitrids perform diving flight displays high above their territory to advertise that the territory is occupied. Some pairs of Accipitrids perform displays together. For example, red-tailed hawk pairs (Buteo jamaicensis) sometimes perform a display in which they glide together, with their legs dangling below them, after they have chased off an intruder from their territory. This display may be involved in both territoriality and courtship, as it is often followed by copulation. If an intruder enters a territory despite the owner’s flight displays, accipitrids use threat displays to discourage them. Threat displays usually involve raising the crest or head feathers, stretching the head and neck forward, and/or opening the wings as well as vocalizations. At the nest, a variety of greeting, solicitation and begging postures and/or vocalizations are used to communicate between the male and female and the parents and chicks.

Although accipitrids are largely silent outside of the breeding season, during breeding they sometimes use calls to communicate with each other. Calls can be used to signal hunger, alarm or location, to solicit copulation or while defending a territory or engaged in an aggressive interaction. Calls are usually only heard during the breeding season, and rarely at other times of the year.

Members of the Accipitridae have eyesight that is four to eight times better than that of humans. This visual acuity allows them to spot prey from far away. For example, eagles are able to spot a vole or lizard from more than 400 m away. Accipitrids rely heavily on their acute eyesight for catching prey. It is by far, the most important sense they use for hunting. However, they also use hearing to detect prey, and are attracted to the calls of their prey. There is little evidence that smell is an important way that raptors sense their environment. Even the carrion-specializing vultures do not have a well-developed sense of smell.

Communication Channels: visual ; acoustic

Perception Channels: visual ; tactile ; acoustic ; chemical

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Life Expectancy

The average lifespan for most raptors is one to two years, though it is likely to be longer for some larger species. The oldest known free-living accipitrid lived to age 38. In captivity, large eagles and vultures have lived up to 60 years.

The mortality rate of accipitrid nestlings (during the period between hatching and fledging) is between 20 and 40 percent. The vast majority of this mortality is due to food shortage and/or siblicide, though predation can also be a significant source of mortality. The period immediately following fledging is the time of highest mortality during a raptor’s life. This is the time when the young bird is still mastering the arts of flying and hunting. Estimates of mortality for the interval between fledging and acquisition of adult plumage range as high as 90 percent for some species. Likely sources of mortality during this period include starvation, predation, disease and accidents.

Estimates of annual adult mortality for accipitrids range from 65 to 90 percent. Generally, annual survival is higher in larger species and lower in smaller species. Sources of mortality for accipitrids have historically included deliberate shootings, poisoning and trapping. More recently, these sources of mortality have declined. However, Accipitrids still die from electrocution (power lines), collisions with vehicles and wind turbines, and poisoning from pesticides or from poisoned carcasses intended for other predators.

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Reproduction

Most accipitrids are monogamous, and many mate for life. Though polygyny and polyandry do occur regularly in some species, these species are exceptional. Most species of Accipitridae are solitary, and defend a territory around their nest. The size of a pair's territory and the extent to which they defend it from conspecifics depends on the species and the habitats. In general, open-country species chase-off intruders more than forest-dwelling species, probably because intruders are more difficult to detect in forested habitat. Colonial breeding does occur in some species at sites with high prey abundance and suitable nest-sites. North American examples of these species include northern harriers and snail kites.

All accipitrids build nests, which the male and female construct together. The male brings most of the nest material to the female, who arranges it at the nest site. In most species, the male also provides the majority of food to the female from the pre-laying stage up through much of the nestling stage. Provision of food by the male may be an important part of courtship during the pre-laying and laying stages. Copulation occurs before and during the time of egg laying. Several hundred copulations may take place during this period. Courtship behavior by males includes bringing food and nest materials to the female, and performing flight displays above the territory or nest. Males and females of some species also display together. The female may solicit copulation from the male by assuming solicitous postures.

Mating System: monogamous ; polyandrous ; polygynous ; cooperative breeder

Accipitrids reach sexual maturity between ages one and nine. Generally, small species become sexually mature in their first year whereas larger species take longer to mature. In species that do not reach sexual maturity until they are more than one year old, many young birds spend the first year or more on the wintering grounds rather than returning north for the summer. When they do return north to breed, raptors show high fidelity to their natal breeding site, often settling in the same area or within 100 km of it. Breeding begins in the spring in temperate regions, and during the dry season in tropical regions. In regions where the weather is less predictable, raptors may breed throughout the year, or after weather events that signal an upcoming abundance of food, such as after irregular heavy rains. Accipitrids nest once per breeding season. Some species, mostly Buteos, will re-nest if they experience nest failure soon after egg laying.

Female accipitrids lay between one and nine eggs per breeding season, though clutches bigger than six eggs are exceptional for any species. The number of eggs differs between and within species with food availability and latitude. Larger species usually lay clutches of one to two eggs, where as smaller accipiters and harriers normally lay clutches of five to six eggs. Birds that nest farther from the equator generally lay larger clutches than equatorial individuals of the same species. In many species, especially rodent specialists, clutch size also tends to track prey abundance.

One egg is laid every two to five days, and incubation begins with the first or second egg. Length of the incubation period differs considerably between species, and lasts from 28 to 60 days (longer for larger species). Both the male and female incubate the eggs in most species. Because incubation begins before all eggs have been laid, the eggs hatch asynchronously, and the older chicks are noticeably larger than they younger chicks. The older chicks are able to out-compete the smaller chicks, which often die of starvation or from aggression by the older chicks. This process of brood reduction is obligate in some species, but occurs only in times of food shortage in other species.

Males of most accipitrid species provide the majority of the food to the females and nestlings from the pre-laying stage to about half-way through the nesting period. The female usually feeds the chicks by tearing the food into bite-sized pieces. Young accipitrids begin to leave the nest when they are about a month old. They begin by hopping out of the nest along branches or ledges, and then making short flapping jumps between the nest and nearby perches. The length of these jumps increases until the chick can make short flights to nearby perches. The chicks then begin to spend most of their time away from the nest, perching nearby and returning to the nest to feed. Young birds fledge after a length of time that varies widely between species, but is roughly similar to the length of the incubation period. Fledglings continue to return to the nest to receive food from the parents even after they can fly. After up to several weeks of supplemental feeding from the parents, young birds disperse from their parents territory (though in some species, juveniles will remain in their parents’ territory for up to a year before being chased off by the adults). Juveniles may disperse in any direction, some even heading north, before beginning a southward migration to wintering grounds or finding a place to settle for the winter.

Nest building is one of the characteristics that distinguish accipitrids from falcons. Accipitrids build nests of sticks or twigs and line them with a softer material, such as the inner or outer bark of trees, frayed palm or agave leaves or seaweed. Some species also decorate their nests with fresh green leaves or conifer needles. Nests are built in a tree, on a cliff, or occasionally on the ground. Construction of a nest can take weeks to months, which may explain why nests are often re-used from year to year. Active accipitrid nests are usually easy to spot by the "whitewash" (a layer of excrement) below the nest.

Key Reproductive Features: iteroparous ; seasonal breeding ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); oviparous

Accipitrid parents feed their young from the time of hatching to several weeks after fledging. When the chicks are very small, the female tears food into small pieces, which she feeds to the chicks. In some vultures, the adults instead regurgitate food into the mouths of the chicks. During the nestling period, the male brings food to the nest while the female spends most of her time at the nest protecting, feeding and caring for the chicks. The female begins hunting again about halfway through the nestling stage. The parents continue to bring food to the chicks for several weeks after they have fledged, which allows the chicks to practice flying and hunting while they have a reliable food source. Eventually, the chicks begin to successfully hunt for themselves, and leave the nest soon after this.

While accipitrid chicks are young, the female spends the majority of her time at the nest. In addition to feeding the chicks, she defends them from predators and weather extremes. Young chicks are unable to regulate their body temperature and are dependant on adults to shade them from the sun and cover them in the rain. Females defend the nest by actively chasing off predators and by shielding the contents of the nest from view when predators fly over. Both males and females perform territorial display flights over the hunting/breeding territory to discourage intruders from entering.

Parental Investment: precocial ; male parental care ; female parental care

  • 2003. Hawks and Eagles (Accipitridae). Pp. 317-328 in A Evans, R Garrison, M Hutchins, eds. Grzimek's Animal Life Encyclopedia, Vol. 8. Detroit: Gale Group.
  • Kemp, A., I. Newton. 2003. Hawks, Eagles and Old World Vultures. Pp. 162-175 in C Perrins, ed. The New Encyclopedia of Birds. Oxford: Oxford University Press.
  • Snyder, H. 2001. Hawks and Allies. Pp. 212-224 in C Elphick, J Dunning, D Sibley, eds. The Sibley Guide to Bird Life & Behavior. New York: Alfred A. Knopf, Inc.
  • Thiollay, J. 1994. Family Accipitridae (hawks and eagles). Pp. 52-105 in J del Hoyo, A Elliott, J Sargatal, eds. Handbook of the Birds of the World. Vol. 2. New World Vultures to Guineafowl. Barcelona: Lynx Edicions.
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Evolution and Systematics

Functional Adaptations

Functional adaptation

Nests are parasite-free: eagles
 

The nests of eagles are kept free of parasitic insects by a lining of aromatic leaves.

   
  "Eagles and other birds of prey keep parasitic insects out of their nests by adding aromatic leaves that act as efficient insecticides." (Shuker 2001:216)
  Learn more about this functional adaptation.
  • Shuker, KPN. 2001. The Hidden Powers of Animals: Uncovering the Secrets of Nature. London: Marshall Editions Ltd. 240 p.
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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage

Barcode of Life Data Systems (BOLD) Stats
Specimen Records:875
Specimens with Sequences:738
Specimens with Barcodes:716
Species:128
Species With Barcodes:118
Public Records:557
Public Species:102
Public BINs:95
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Barcode data

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Conservation

Conservation Status

Though accurate worldwide population estimates for most accipitrid species are unavailable, data on well-known species suggests that overall raptor numbers are declining. Sixty of the 237 species in the Accipitridae are listed on The World Conservation Union’s IUCN Red List of Threatened Species. Nine of these are critically endangered, 4 are endangered, 23 are vulnerable, 23 are near threatened and 1 is data deficient.

Human persecution through shooting, trapping and poisoning has historically been the most significant source of raptor mortality. Though such activities are now illegal in most developed countries, and raptors are protected by legislation such as the Migratory Bird Treaty Act, shooting and poisoning continue to be a significant source of raptor mortality. Between the 1940's and 1960's, many accipitrids were poisoned by widely used organochlorine pesticides, such as DDT. These pesticides accumulated in the prey that raptors ingested, and caused population declines in many species. Use of these pesticides has declined sharply, though they continue to be used in many countries where raptors or their prey spend the winter. Populations of many species that were poisoned by organochlorine pesticides during the middle 1900’s are now experiencing dramatic increases.

Habitat loss is the largest threat facing raptor populations today. However, nest disturbance may also be a significant source of local reproductive failure and population decline in raptor species. Repeated disturbances at the nest force adults to spend more time on nest defense, and less time feeding and caring for their young. Disturbance can also cause nest abandonment in shy species, including bald eagles and white-tailed sea-eagles. The many potential sources of nest disturbance include forestry activities, roads, off-road vehicles, recreational activities such as cliff climbing and hang-gliding, low-flying aircraft and military exercises.

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Relevance to Humans and Ecosystems

Benefits

Raptors are known to prey on game species, such as quails, partridges, pheasants and rabbits. They also occasionally take domesticated animals such as lambs and poultry.

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Humans have used raptors (both Accipitrids and falcons) for hunting and recreation in the form of falconry since as early as 2000 BC. Though this practice has largely died, it continues in some areas. Falconers in the United States use northern goshawks, Eurasian sparrowhawks and golden eagles to hunt prey including quails, partridges and pheasants and rabbits and hares.

Wild raptors include game animals and some domesticated animals, such as lambs and poultry among their prey. This led to a long period of widespread discrimination against raptors, beginning in the late 1700’s, and continuing to the 1970’s, when it generally ended in most developed countries. At the height of this period of destruction, roughly between 1860 and 1960, many governments gave rewards for the slaughter of millions of raptors.

Raptors can play an important role as bioindicators of habitat quality and pollution. In fact, they are already used in the tropics to monitor forest degradation. They may also help maintain the dynamics and diversity of ecosystems by lowering numbers of dominant prey, thereby allowing less common prey species to survive.

Eagle feathers are used by various indigenous societies in religious celebrations. Eagle feathers are used in arrows by some of the forest-dwelling tribes in South America. Body parts of many species are used in traditional medicine by healers in many parts of Asia, Africa, and the Caribbean. Raptors have been included in the cuisine of many regions, and are still eaten in Taiwan and the Philippines, as well as China.

Positive Impacts: pet trade ; food ; body parts are source of valuable material; ecotourism ; controls pest population

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Wikipedia

Eagle

Eagle is a common name for some 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 sixty species occur in Eurasia and Africa.[1] Outside this area, just eleven species can be found - two species (the Bald Eagle and Golden Eagle) in the United States and Canada, nine species in Central America and South America, and three species in Australia.

Contents

Description

Eagles are large, powerfully built birds of prey, with a heavy head and beak. Even the smallest eagles, like the Booted Eagle (Aquila pennata) (which is comparable in size to a Common Buzzard (Buteo buteo) or Red-tailed Hawk (B. jamaicensis)), have relatively longer and more evenly broad wings, and more direct, faster flight. (Despite reduced size in aerodynamic feathers) Most eagles are larger than any other raptors apart from some vultures. The smallest species called eagle is the South Nicobar Serpent Eagle (Spilornis klossi), at 450 g (1 lb) and 40 cm (16 in). The largest species are discussed below. Like all birds of prey, eagles have very large hooked beaks for tearing flesh from their prey, strong muscular legs, and powerful talons. The beak is typically heavier than most other birds of prey. They also have extremely keen eyesight (up to 3.6 times human acuity for the martial eagle) which enables them to spot potential prey from a very long distance.[2] This keen eyesight is primarily contributed by their extremely large pupils which ensure minimal diffraction (scattering) of the incoming light. The female of all species of eagle known are larger than the male.[3][4]

Eagles normally build their nests, called eyries, in tall trees or on high cliffs. Many species lay two eggs, but the older, larger chick frequently kills its younger sibling once it has hatched. The dominant chick tends to be the female, as they are bigger than the male. The parents take no action to stop the killing.[5][6]

Due to the size and power of many eagle species, they are ranked at the top of the food chain as apex predators amongst the avian world. The type of prey varies from genus to genus. The Haliaeetus and Ichthyophaga eagles prefer to capture fish, though the species in the former often capture various animals, especially other water birds, and are powerful kleptoparasites of other birds. The snake and serpent eagles of the genera Circaetus, Terathopius and Spilornis predominantly prey on the great diversity of snakes that are found in the tropics of Africa and Asia. The eagles of the genus Aquila are often the top birds of prey in open habitats, taking almost any medium-sized vertebrate they can catch. Where Aquila eagles are absent, other eagles, such as the buteonine Black-chested Buzzard-Eagle of South America, may assume the position of top raptorial predator in open areas. Many other eagles, including the species-rich Spizaetus genus, live predominantly in woodlands and forest. These eagles often target various arboreal or ground-dwelling mammals and birds, which are often unsuspectingly ambushed in such dense, knotty environments. Hunting techniques differ among the species and genera, with some individual eagles having engaged in quite varied techniques based their environment and prey at any given time. Most eagles grab prey without landing and take flight with it so the prey can be carried to a perch and torn apart.[7] The Bald Eagle is noted for having flown with the heaviest load verified to be carried by any flying bird, since one eagle flew with a 6.8 kg (15 lb) mule deer fawn.[8] However, a few eagles may target prey considerably heavier than themselves, which are too heavy to fly with and thus it is eaten at the site they kill it or taken in pieces back to a perch or a nest. Golden and Crowned Eagles have killed ungulates weighing up to 30 kg (66 lb) and a Martial Eagle even killed a 37 kg (82 lb) duiker, 7-8 times heavier than the predating eagle.[7][9] Authors on birds David Allen Sibley, Pete Dunne and Clay Sutton, described the behaviorial difference between hunting eagles and other birds of prey thusly (in this case the Bald and Golden Eagles as compared to other North American raptors):[10]

They have at least one singular characteristic. It has been observed that most birds of prey look back over their shoulders before striking prey (or shortly thereafter); predation is after all a two-edged sword. All hawks seem to have this habit, from the smallest kestrel to the largest Ferruginous - but not the Eagles.

Among the eagles are some of the largest birds of prey: only the condors and some of the Old World vultures are markedly larger. It is regularly debated which could be considered the largest species of eagle. They could be measured variously in total length, body mass or wingspan. Different lifestyle needs among various eagles result in variable measurements from species to species. For example, many forest-dwelling eagles, including the very large Harpy and Philippine Eagles, have relatively short wingspans, a feature necessary for being able to maneuver in quick, short bursts through dense forested habitats.[7] On the other hand, eagles in the genus Aquila are found almost strictly in open country, are superlative soarers, and have relatively long wings for their size.[7]

Here are lists of the top five eagles going on weight, length and, lastly, wingspan. Unless otherwise noted via reference, the figures listed are the median reported for each measurement in the guide Raptors of the World (Ferguson-Lees, et al.), in which only measurements that could be personally verified by the authors were listed.[7]

RankCommon NameScientific NameBody Mass
1Steller's Sea EagleHaliaeetus pelagicus6.7 kilograms (15 lb)
2Philippine EaglePithecophaga jefferyi6.35 kg (14.0 lb)
3Harpy EagleHarpia harpyja5.95 kg (13.1 lb)
4White-tailed EagleHaliaeetus albicilla4.8 kg (11 lb)[11]
5Martial EaglePolemaetus bellicosus4.6 kg (10 lb)[11]
RankCommon NameScientific NameTotal Length
1Philippine EaglePithecophaga jefferyi100 cm (3 ft 3 in)[12]
2Harpy EagleHarpia harpyja95.5 cm (3 ft 2 in)
3Wedge-tailed EagleAquila audax95.5 cm (3 ft 2 in)
4Steller's Sea EagleHaliaeetus pelagicus95 cm (3 ft 1 in)
5Crowned EagleStephanoaetus coronatus87.5 cm (2 ft 10 in)
RankCommon NameScientific NameMedian Wingspan
1White-tailed EagleHaliaeetus albicilla218.5 cm (7 ft 2 in)
2Steller's Sea EagleHaliaeetus pelagicus212.5 cm (7 ft 0 in)
3Wedge-tailed EagleAquila audax210 cm (6 ft 11 in)[13][14]
4Golden EagleAquila chrysaetos207 cm (6 ft 9 in)
5Martial EaglePolemaetus bellicosus206.5 cm (6 ft 9 in)

Species

Martial Eagle in Namibia
Philippine Eagle, Pithecophaga jefferyi in Southern Philippines
Wedge Tailed Eagle in Australia

Major new research into eagle taxonomy suggests that the important genera Aquila and Hieraaetus are not composed of nearest relatives, and it is likely that a reclassification of these genera will soon take place, with some species being moved to Lophaetus or Ictinaetus.[15]

FAMILY Accipitridae

Short-toed Snake Eagle in flight

Eagles in culture

The modern English name of the bird is derived from the Latin term aquila by way of the French aigle. The Latin aquila may derive from the word aquilus, meaning dark-colored, swarthy, or blackish, as a description of the eagle's plumage; or from aquilo, the Latin version of Greek boreas, or north wind; however, aquilus and aquilo may just as well derive from aquila (or be unrelated) and the latter be of unknown origin.

Old English used the term earn, related to Scandinavia's ørn / örn. The etymology of this word relates it to Greek ornís, meaning "bird", though other Indo-European languages (such as Welsh eryr or Russian orël / орёл) show that the meaning 'eagle' is older. The Greek word may be an old diminutive. The Albanian word for eagle is "shqiponje" deriving from the root "shqipe", which means "eagle".

In Britain before 1678, eagle referred specifically to the Golden Eagle, with the other native species, the White-tailed Eagle, being known as the Erne. The modern name "Golden Eagle" for aquila chrysaetos was introduced by the naturalist John Ray.

Religion

Garuda, the Vahana of Lord Vishnu, depicted with an eagle's beak and wings

The Moche people of ancient Peru worshiped the animal and often depicted eagles in their art.[17]

Despite modern and historic Native American practices of giving eagle feathers to non-indigenous people and also members of other tribes who have been deemed worthy, current United States eagle feather law stipulates that only individuals of certifiable Native American ancestry enrolled in a federally recognized tribe are legally authorized to obtain eagle feathers for religious or spiritual reasons.[18] In Canada, poaching of eagle feathers for the booming U.S. market has sometimes resulted in the arrests of First Nations person for the crime.[19]

In Hindu religion, Garuda is a lesser Hindu divinity, usually the mount (vahanam) of Vishnu. Garuda is depicted as having the golden body of a strong man with a white face, red wings, and an eagle's beak and with a crown on his head. This ancient deity was said to be massive, large enough to block out the sun.

The eagle is also the patron animal of Zeus. In particular, Zeus was said to have taken the form of an eagle in order to abduct Ganymede, and there are numerous artistic depictions of the Eagle Zeus bearing Ganymede aloft, from Classical times up to the present (see illustrations in the Ganymede (mythology) page.)

The Eagle is also the symbol of Libby, Montana which was recently named "The City of Eagles"[20][21]

Eagles as national symbols

The coat of arms of Mexico - a golden eagle perched upon a cactus eating a snake
The coat of arms of Austria - a black eagle holding a hammer and a sickle, with a broken chain between its legs

Eagles have been used by many nations as a national symbol.

Historic uses:

References

  1. ^ del Hoyo, J.; Elliot, A. & Sargatal, J. (editors). (1994). Handbook of the Birds of the World Volume 2: New World Vultures to Guineafowl. Lynx Edicions. ISBN 84-87334-15-6
  2. ^ Shlaer, Robert (1972-05-26). "An Eagle's Eye: Quality of the Retinal Image". Science 176 (4037): 920–922. doi:10.1126/science.176.4037.920. PMID 5033635. http://www.csee.wvu.edu/~xinl/library/papers/biology/eagle_eyes.pdf. Retrieved 2012-04-16. 
  3. ^ Georges Louis Leclerc, Comte de Buffon; Comte De Buffon (25 November 2010). The Natural History of Birds: From the French of the Count de Buffon; Illustrated with Engravings, and a Preface, Notes, and Additions, by the Translator. Cambridge University Press. pp. 60–. ISBN 978-1-108-02298-9. http://books.google.com/books?id=sFmrk6_RBg8C&pg=PA60. Retrieved 18 February 2012. 
  4. ^ Rebecca L. Grambo (14 December 2003). Eagles. Voyageur Press. ISBN 978-0-89658-363-4. http://books.google.com/books?id=O5J8JK07QykC. Retrieved 18 February 2012. 
  5. ^ Grambo, Rebecca L (2003). Eagles. Voyageur Press. p. 32. ISBN 978-0-89658-363-4. 
  6. ^ Stinson, Christopher H (1979). "On the Selective Advantage of Fratricide in Raptors". Evolution 33 (4): 1219–1225. doi:10.2307/2407480. 
  7. ^ a b c d e Ferguson-Lees, J.; Christie, D. (2001). Raptors of the World. London: Christopher Helm. ISBN 0-7136-8026-1. 
  8. ^ "Amazing Bird Records". Trails.com. http://www.trails.com/arts/amazing-bird-records.aspx. Retrieved 2012-07-20. 
  9. ^ Watson, Jeff (2011). The Golden Eagle: Second Edition. ISBN 978-0=30017-019-1. 
  10. ^ Sutton, C.; Dunne, P.; Sibley, D. (1989). Hawks in Flight: The Flight Identification of North American Migrant Raptors. Boston: Houghton Mifflin Harcourt. ISBN 0-3955-1022-8. 
  11. ^ a b del Hoyo, J; Elliot, A; Sargatal, J (1996). Handbook of the Birds of the World. 3. Barcelona: Lynx Edicions. ISBN 84-87334-20-2. 
  12. ^ Gamauf, A., Preleuthner, M., and Winkler, H. (1998). Philippine Birds of Prey: Interrelations among habitat, morphology and behavior. The Auk 115(3): 713-726
  13. ^ [1]
  14. ^ Wood, Gerald (1983). The Guinness Book of Animal Facts and Feats. ISBN 978-0-85112-235-9. 
  15. ^ Lerner, H. R. L.; D. P. Mindell (2005). "Phylogeny of eagles, Old World vultures, and other Accipitridae based on nuclear and mitochondrial DNA". Molecular Phylogenetics and Evolution 37 (2): 327–346. doi:10.1016/j.ympev.2005.04.010. PMID 15925523. 
  16. ^ Bunce, M.; et al. (2005). "Ancient DNA Provides New Insights into the Evolutionary History of New Zealand's Extinct Giant Eagle". PLoS Biol 3 (1): e9. doi:10.1371/journal.pbio.0030009. PMC 539324. PMID 15660162. http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371%2Fjournal.pbio.0030009. Retrieved 2006-12-27. 
  17. ^ Berrin, Katherine & Larco Museum. The Spirit of Ancient Peru:Treasures from the Museo Arqueológico Rafael Larco Herrera. New York: Thames and Hudson, 1997.
  18. ^ Office of Law Enforcement. "National Eagle Repository". Mountain-Prairie Region. United States Fish and Wildlife Service. Archived from the original on 2007-10-10. http://web.archive.org/web/20071010032432/http://www.fws.gov/mountain-prairie/law/le65.html. Retrieved 2007-11-20. 
  19. ^ Sin, Lena (2006-04-30). "Charges laid in eagle-poaching case". The Province (CanWest MediaWorks Publications Inc.). http://www.canada.com/theprovince/news/story.html?id=7037508c-70c7-4c47-9d3e-713a118e6b66&k=55151. Retrieved 2007-11-20. 
  20. ^ Berget, Todd. "Custom Iron Eagles". http://www.customironeagles.com. 
  21. ^ http://www.roadsideamerica.com/tip/24350 Libby, Montana: City of Eagles]

Further reading

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Kite (bird)

Kite is a common name for birds of the family Accipitridae.

A few of the Perninae are also called kites.

In Mythology

Isis is said in Ancient Egyptian mythology to have taken the form of a kite in various situations in order to resurrect the dead.

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Accipitridae

Accipitridae!<-- This template has to be "warmed up" before it can be used, for some reason -->

Life

The Accipitridae, one of the two major families within the order Accipitriformes (the diurnal birds of prey), are a family of small to large birds with strongly hooked bills and variable morphology based on diet. They feed on a range of prey items from insects to medium-sized mammals, with a number feeding on carrion and a few feeding on fruit. The Accipitridae have a cosmopolitan distribution, being found on all the world's continents (except Antarctica) and a number of oceanic island groups. Some species are migratory.

Many well-known birds, such as hawks, eagles, kites, harriers and Old World vultures are included in this group. The Osprey is usually placed in a separate family (Pandionidae), as is the Secretary bird (Sagittariidae), and the New World vultures are also usually now regarded as a separate family or order. Karyotype data[1] indicated that the accipitrids hitherto analysed are indeed a distinct monophyletic group, but whether this group should be considered a family of the Falconiformes or one or several order(s) on their own is a matter of taste.

Contents

Systematics

The accipitrids have been variously divided into some 5–10 subfamilies. Most share a very similar morphology, but many of these groups contain taxa which are more aberrant. These are placed in their respective position more for lack of better evidence than anything else. It is thus not very surprising that the phylogenetic layout of the accipitrids has always been a matter of dispute.

As mentioned above, the accipitrids are recognisable by a peculiar rearrangement of their chromosomes. Apart from this, morphology and mtDNA cytochrome b sequence data gives a confusing picture of these birds' interrelationships. What can be said is that the hawks, kites, eagles and Old World vultures as presently assigned in all likelihood do not form monophyletic groups:

According to the molecular data, the Buteoninae are most likely poly- or paraphyletic, with the true eagles, the sea eagles, and the buteonine hawks apparently representing distinct lineages. These appear to form a group with the Milvinae, Accipitrinae and Circinae but the exact relationships between the lineages are not at all robustly resolvable with the present data. The Perninae and possibly the Elaninae are older lineages, as are the Old World vultures. The latter are fairly likely also poly- or paraphyletic, with some aberrant species like the Bearded and Egyptian Vultures standing apart from the naked-necked "(not so)true" vultures.[2]

Morphology

Portrait of a Bald Eagle showing its strongly hooked beak and the cere covering the base of the beak.

The Accipitridae are a diverse family with a great deal of variation in size and shape. They range in size from the tiny Pearl Kite and Little Sparrowhawk, both of which are 23 cm in length and weigh about 85 g, to the Cinereous Vulture, which measures 108 cm and weighs 10 kg. Until the 14th century even these were surpassed by the extinct Haast's Eagle of New Zealand, which is estimated to have weighed 14 kg.[3] Most Accipitridae exhibit sexual dimorphism in size, although unusually for birds it is the females that are larger than the males.[4] This sexual difference in size is more pronounced in active species that hunt birds, and is less pronounced in rodent hunters, and almost non-existent in carrion or snail eaters.

The beaks of accipitrids are strong, hooked (sometimes very hooked, as in the Hook-billed Kite or Snail Kite). In some species there is a notch or 'tooth' in the upper mandible. In all accipitrids the base of the upper mandible is covered by a fleshy membrane called the cere which is usually yellow in colour. The tarsi of different species vary by diet, those of bird hunting species like sparrowhawks are long and thin, while species that hunt large mammals have much thicker, stronger ones, and snake-eagle have thick scales to protect from bites.

The plumage the Accipitridae can be striking but rarely utilises bright colours; most birds use combinations of grey, buff and brown.[5] Overall they tend to be paler below, which helps them seem less conspicuous when seen from below. There is seldom sexual dimorphism in plumage, when it occurs the males are brighter or the females resemble juveniles. In many species juveniles have a distinctly different plumage. Some accipitrids mimic the plumage patterns of other hawks and eagles. They may attempt to resemble a less dangerous species to fool prey, or instead resemble a more dangerous species in order to reduce mobbing by other birds.[6] Several species of accipitrid have crests used in signalling, and even species without crests can raise the feathers of the crown when alarmed or excited. In contrast most of the Old World vultures possess bare heads without feathers; this is thought to prevent soiling on the feathers and aid in thermoregulation.[7]

The senses of the Accipitridae are adapted to hunting (or scavenging), and in particular their vision is legendary. The sight of some hawks and eagles is up to 8 times better than that of humans. Large eyes with two fovea provide binocular vision and a "hawk eye" for movement and distance judging. In addition have the largest pectens of any birds. The eyes are tube shaped and cannot move much in their sockets. In addition to excellent vision many species have excellent hearing, but unlike in owls sight is generally the principal sense used for hunting. Hearing may be used to locate prey hidden in vegetation, but sight is still used to catch the prey. Like most birds the Accipitridae generally have a poor sense of smell; even the Old World vultures make no use of the sense, in contrast to the New World vultures in the family Cathartidae.

Diet and feeding

The Palm-nut Vulture is an unusual frugivorous accipitrid , but will also consume fish, particularly dead fish.
Oriental Honey-buzzard Pernis ptilorhyncus

Accipitrids are predominately predators and most species actively hunt for their prey. A few species may opportunistically feed on fruit and in one species, the Palm-nut Vulture, it forms the major part of the diet.[8] However other animals form the bulk of the diet of most species. Insects are taken exclusively by around 12 species, in great numbers by 44 additional species, and opportunistically by many others.[5] The diet of the honey-buzzards includes not only the adults and young of social insects such as wasps and bees, but the honey and combs from their nests.[9] The Snail Kite and Hook-billed Kites are specialists in consuming snails. Bazas and forest hawks in the genus Accipiter may take reptiles from trees whilst other species hunt them on the ground. Snakes in particular are targeted by the snake-eagles (Circaetus) and serpent-eagles (Spilornis and Dryotriorchis).[5]

Genera

Fossil record

Neophrontops americanus fossil

Like with most other birds of prey, the fossil record of this group is fairly decent from the latter Eocene onwards (c.35 mya), with modern genera being well documented since the Early Oligocene, or around 30 mya.

Accipitrids are known since Early Eocene times, or about from 50 mya onwards, in fact, but these early remains are too fragmentary and/or basal to properly assign a place in the phylogeny. Likewise, as remarked above, molecular methods are of limited value in determining evolutionary relationships of and within the accipitrids. What can be determined is that in all probability, the group originated on either side of the Atlantic, which during that time was only 60-80% its present width. On the other hand, as evidenced by fossils like Pengana, some 25 mya, accipitrids in all likelihood rapidly acquired a global distribution - initially probably even extending to Antarctica.

  • Accipitridae gen. et sp. indet. (Huerfano Early Eocene of Huerfano County, USA)[11]
  • Accipitridae gen. et sp. indet. (Borgloon Early Oligocene of Hoogbutsel, Belgium)[12]
  • Accipitridae gen. et sp. indet. (Bathans Early/Middle Miocene of Otago, New Zealand)[13]
  • Accipitridae gen. et sp. indet. MPEF-PV-2523 (Puerto Madryn Late Miocene of Estancia La Pastosa, Argentina)
  • "Aquila" danana (Snake Creek Late Miocene/Early Pliocene of Loup Fork, USA) - formerly also Geranoaetus or Buteo
  • Accipitridae gen. et sp. indet. (Early/Middle Pliocene of Kern County, USA) - Parabuteo?[14]
  • Accipitridae gen. et sp. indet. (Late Pliocene/Early Pleistocene of Ibiza, Mediterranean) - Buteo?[15]
  • Accipitridae gen. et sp. indet. (Egypt)

Specimen AMNH FR 2941, a left coracoid from the Late Eocene Irdin Manha Formation of Chimney Butte (Inner Mongolia) was initially assessed as a basal mid-sized "buteonine";[16] it is today considered to be more likely to belong in the Gruiformes genus Eogrus.[17] The Early Oligocene genus Cruschedula was formerly thought to belong to Spheniscidae, however reexamination of the holotype in 1943 resulted in the genus being placed in Accipitridae.[18] Further examination in 1980 resulted in placement as Aves incertae sedis.[19]

Footnotes

  1. ^ de Boer (1975), Amaral & Jorge (2003), Federico et al. (2005)
  2. ^ Wink et al. (1996)
  3. ^ Brathwaite (1992)
  4. ^ Paton et al. (1994)
  5. ^ a b c Thiollay (1994)
  6. ^ Negro (2008)
  7. ^ Ward et al.(2008)
  8. ^ Although not the entire diet. Thomson et al. 1957
  9. ^ Shiu (2006)
  10. ^ a b c d e f g h i Lerner & Mindell, 2005
  11. ^ Specimen AMNH FR 7434: Left carpometacarpus of a Snail Kite-sized bird: Cracraft (1969)
  12. ^ Tarsometatarsus of a bird the size of an Eurasian Sparrowhawk: Smith (2003)
  13. ^ Specimens MNZ S42490, S42811: Distal left tibiotarsus and distal right ulna of a bird the size of a smallish eagle: Worthy et al. (2007)
  14. ^ Distal tibia quite similar to Harris's Hawk: Miller (1931)
  15. ^ Alcover (1989)
  16. ^ Wetmore (1934)
  17. ^ AMNH (2007)
  18. ^ Simpson, G.G. (1946). "Fossil penguins". Bulletin of the American Museum of Natural History 81. http://digitallibrary.amnh.org/dspace/bitstream/2246/392/1/B087a01.pdf. 
  19. ^ Olson, S.L. (1985). "Faunal Turnover in South American Fossil Avifaunas: The Insufficiencies of the Fossil Record". Evolution 39 (5): 1174–1177. http://si-pddr.si.edu/dspace/bitstream/10088/6499/1/VZ_169_S_Amer_fossil_avifaunas.pdf. 

References

  • Alcover, Josep Antoni (1989): Les Aus fòssils de la Cova de Ca Na Reia ["The fossil birds of Ca Na Reia cave"]. Endins 14-15: 95-100. [Catalan with English abstract]
  • Amaral, Karina Felipe & Jorge, Wilham (2003): The chromosomes of the Order Falconiformes: a review. Ararajuba 11(1): 65-73. PDF fulltext
  • American Museum of Natural History (AMNH) (2007): AMNH FR 2941 specimen information. Retrieved 2008-APR-22.
  • Brathwaite, D. H. (1992): "Notes on the weight, flying ability, habitat, and prey of Haast's Eagle (Harpagornis moorei)". Notornis 39(4): 239–247.
  • Cracraft, Joel (1969): Notes on fossil hawks (Accipitridae). Auk 86(2): 353-354. PDF fulltext
  • de Boer, L.E.M. (1975): Karyological heterogeneity in the Falconiformes (Aves). Cellular and Molecular Life Sciences 31(10): 1138-1139. doi:10.1007/BF02326755 (HTML abstract)
  • Federico, Concetta; Cantarella, Catia Daniela; Scavo, Cinzia; Saccone, Salvatore; Bed'Hom, Bertrand & Bernardi, Giorgio (2005): Avian genomes: different karyotypes but a similar distribution of the GC-richest chromosome regions at interphase. Chromosome Research 13(8): 785-793. doi:10.1007/s10577-005-1012-7 (HTML abstract)
  • Lerner , Heather R.L. & David P. Mindell (2005): Phylogeny of eagles, Old World vultures, and other Accipitridae based on nuclear and mitochondrial DNA. Molecular Phylogenetics and Evolution 37:327–346 PDF fulltext
  • Miller, Loye H. (1931): Bird Remains from the Kern River Pliocene of California. Condor 33(2): 70–72. PDF fulltext
  • Negro, J.J. (2008) Two aberrant serpent-eagles may be visual mimics of bird-eating raptors Ibis 150 (2): 307–314 doi:10.1111/j.1474-919X.2007.00782.x
  • Paton, P.W.C.; Messina, F.J. & C.R. Griffin (1994): A Phylogenetic Approach to Reversed Size Dimorphism in Diurnal Raptors. Oikos 71 (3): 492-498
  • Shiu, Hau-Jie; Ken-ichi Tokita, Emiko Morishita, Emiko Hiraoka, Yinyin Wu, Hiroshi Nakamura and Hiroyoshi Higuchi (2006) "Route and site fidelity of two migratory raptors: Grey-faced Buzzards Butastur indicus and Honey-buzzards Pernis apivorus" Ornithological Science 5 (2): 151-156 doi:10.2326/osj.5.151
  • Smith, Richard (2003): Les vertébrés terrestres de l'Oligocène inférieur de Belgique (Formation de Borgloon, MP 21): inventaire et interprétation des données actuelles. [Early Oligocene terrestrial vertebrates from Belgium (Borgloon Formation, MP 21): catalog and interpretation of recent data.] Coloquios de Paleontología E1: 647-657. [French with English abstract] PDF fulltext
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