The ACCIPITRIDAE, one of the four families within the order
Accipitriformes (the others being
Sagittariidae ), 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
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 indicate the
accipitrids analysed are indeed a distinct monophyletic group, but
whether this group should be considered a family or one or several
order(s) on their own is a question still to be resolved.
* 1 Systematics
* 2 Morphology
* 3 Diet and behavior
* 4 Reproductive biology and populations
* 5 Genera
* 6 Footnotes
* 7 References
* 8 External links
The accipitrids have been variously divided into some five to 10
subfamilies . Most share a very similar morphology , but many of these
groups contain taxa that 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.
The accipitrids are recognizable by a peculiar rearrangement of their
chromosomes . Apart from this, morphology and mtDNA cytochrome b
sequence data give a confusing picture of these birds'
interrelationships. What can be said is that the hawks , kites ,
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
Accipitrinae and Circinae
but the exact relationships between the lineages are not at all
robustly resolvable with the present data. The
Perninae and possibly
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 "true" vultures.
Portrait of a bald eagle , showing its strongly hooked beak and
the cere covering the base of the beak.
Accipitridae are a diverse family with a great deal of variation
in size and shape. They range in size from the tiny pearl kite
Gampsonyx swainsonii) and little sparrowhawk (
both of which are 23 cm (9 in) in length and weigh about 85 g (3 oz),
to the cinereous vulture (
Aegypius monachus), which measures up to 120
cm (47 in) and weighs up to 14 kg (31 lbs). Wingspan can vary from 39
cm (15 in) in the little sparrowhawk to more than 300 cm (120 in) in
the cinereous and Himalayan vultures (
Gyps himalayensis). In these
extreme species, wing chord length can range from 113 to 890 mm (4.4
to 35.0 in) and culmen length from 11 to 88 mm (0.43 to 3.46 in).
Until the 14th century, even these huge vultures were surpassed by the
extinct Haast\'s eagle (Harpagornis moorei) of New Zealand, which is
estimated to have measured up to 140 cm (55 in) and to have weighed 15
to 16.5 kg (33 to 36 lb) in the largest females. In terms of body
Accipitridae are the most diverse family of birds and may
also be in terms of some aspects of linear size diversity, although
lag behind the true parrots and pheasant family in length diversity.
Most accipitrids exhibit sexual dimorphism in size, although,
unusually for birds, it is the females that are larger than the males.
This sexual difference in size is most pronounced in active species
that hunt birds, such as the
Accipiter hawks, in which the size
difference averages 25–50%. In a majority of species, such as
generalist hunters and rodent -, reptile -, fish -, and insect
-hunting specialists, the dimorphism is less, usually between a 5% to
30% size difference. In the carrion-eating
Old World vultures and
snail eating kites , the difference is almost non-existent.
The beaks of accipitrids are strong and 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, such as
sparrowhawks, are long and thin, whilst species that hunt large
mammals have much thicker, stronger tarsi, and the tarsi of the
snake-eagles have thick scales to protect from bites.
The plumage of the
Accipitridae can be striking, but rarely utilises
bright colours; most birds use combinations of grey, buff and brown.
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. 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
Old World vultures possess bare heads without feathers; this is
thought to prevent soiling on the feathers and aid in thermoregulation
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 they 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
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
DIET AND BEHAVIOR
Palm-nut vulture is an unusual frugivorous accipitrid, but will
also consume fish, particularly dead fish Shikra Accipiter
Hyderabad, India Oriental honey-buzzard Pernis
Accipitrids are predominantly predators and most species actively
hunt for their prey. Prey is usually captured and killed in the
powerful talons of the raptor and then carried off to be torn apart
with a hooked bill for eating or feeding to nestlings. A majority of
accipitrids are opportunistic predators that will take any prey that
they can kill. However, most have a preference for a certain type of
prey, which in harriers and the numerous buteonine hawks (including
more than 30 species in the
Buteo genus) tends towards small mammals
such as rodents .
Among the raptors that mainly favor small mammals, harriers generally
hunt by hovering over openings until they detect their prey and
descend upon them. Due to the specificity of their hunting style, prey
preferences, and habitat preferences, usually only one harrier species
tends to be found per region.
Buteonine hawks usually watch for prey from a perch but most species
will also readily hunt on the wing, including from a high soar. Many
buteonines are amongst the most generalized feeders, often feeding on
any active small animal they find, and will generally eat whatever
diurnal rodent or lagomorph is most locally common. Although, some
buteonines are more specialized, such as some species in the
Buteogallus genus, which have evolved to specialize in feeding on
crabs . Larger Buteogallus, namely the solitary eagles , and
Geranoaetus , are much larger than other buteonines and seem to have
become avian apex predators of specific habitat niches, i.e. savanna ,
cloud forest and páramo in
South America and are thus honorary
Accipiter hawks (the most species-rich accipitrid genus with
nearly 50 extant species), prey is mainly other birds . Accipiters are
in general forest- and thicket-dwelling species.
usually ambush birds in dense vegetation, a dangerous hunting method
that requires great agility. Many smaller tropical species of
Accipiter eat nearly equal portions of insects and reptiles and
amphibians as they do of birds while some of the larger species have
become more generalized, and may feed extensively on rodents and
lagomorphs as well as other various non-avian animals.
Most accipitrids will supplement their diet with non-putrid carrion
but, of course, none specialized with this as well as the 14-16
species of vultures , which have evolved very large bodies (which
leave them equipped to fill their crop with carrion), weaker, less
specialized feet relative to other accipitrids, large wingspans to
spend extensively periods of time in flight over openings scanning for
carcasses and complex social behavior in order to establish a mixed
species hierarchy at carrion. The New World vultures have attained
several similar characteristics, but only through convergent evolution
and are seemingly not directly related to
Old World vultures and other
accipitrids. The lammergeier (
Gypaetus barbatus) is an aberrant cousin
Old World vultures that has maintained strong feet in order to
carry and drop large bones in order to crack them open to feed on bone
marrow, their primary food, a technique they also sometimes use for
live prey items, like tortoises .
A few species may opportunistically feed on fruit. In one species,
the palm-nut vulture (
Gypohierax angolensis) (possibly not closely
related to other "vultures"), it may form more than half of the diet.
Most accipitrids will not eat plant material.
Insects are taken exclusively by around 12 species, in great numbers
by 44 additional species, and opportunistically by a great many
others. 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.
The snail kite (
Rostrhamus sociabilis), slender-billed kite
Helicolestes hamatus) and hook-billed kites (
are specialists in consuming snails , which usually constitute 50-95%
of their diet. Other "kites " are divided into two groups, a loose
assemblance of smallish raptors, many of which are strong fliers. One,
exclusively in the Old World, milvine or "large" kites, are relatively
large, often quite common, very generalized and often weakly
predaceous feeders whereas the other kites, also known as elanine or
"small" kites and mostly found in the New World, are supremely aerial,
active hunters that generally alternate their primary food between
insects and small mammals. One species allied with the latter kite
group, the bat hawk (Macheiramphus alcinus), has come to specialize in
hunting bats .
"Eagles " are several raptors that are not necessarily closely
related, but can be broadly defined by large body size (larger than
other raptors excluding vultures) and the taking of typically larger
prey, including mid-sized mammals and larger birds. The most diverse
group of eagles is the "booted eagles", a variable group of c. 30
species, defined by their feathering covering their legs (shared by
only a couple of buteonine species).
Most accipitrids usually hunt prey rather smaller than themselves.
However, many accipitrids of almost all sizes have been recorded as
capturing and then flying with prey of equal weight or even slightly
heavier than themselves in their talons, a feat that requires great
physical strength. Occasionally, an eagle or other raptor that kills
prey considerably heavier than itself (too heavy for the raptor to
carry and fly with) will then have to leave prey where they've killed
and later return repeatedly to feed or dismember and bring to a perch
or nest piece by piece. This has the advantage of providing a surplus
of food but has the disadvantage of potentially attracting scavengers
or other predators which can steal the kill or even attack the feeding
accipitrid. Using this method, accipitrids such as the golden (Aquila
chrysaetos), wedge-tailed (Aquila rapax), martial (Polemaetus
bellicosus) and crowned eagles (
Stephanoaetus coronatus) have
successfully hunted ungulates , such as deer and antelope , and other
large mammals (kangaroos and emus in the wedge-tailed) weighing more
than 30 kg (66 lb), 7–8 times their own mass. More typical prey for
these powerful booted eagle species weigh between 0.5 and 5 kg (1.1
and 11.0 lb).
Haliaeetus eagles, the
Ichthyophaga eagles and the osprey
(Pandion haliaetus), possibly in its own monotypical family, mainly
prefer to prey on fish (comprising more than 90% of food for the
latter 2 genera). These large acciptrids may supplement their diets
with aquatic animals other than fish, especially the more generalized
Haliaeetus eagles, which also hunt large numbers of water birds and
are expert kleptoparasites .
Reptiles and amphibians are hunted by almost all variety of
acciptrids when the opportunity arises and may be favored over other
prey by some eagles, i.e.
Spizaetus hawk-eagles and the "eagles" in
Buteogallus , and several species of buteonine hawks found in the
tropics. Bazas and forest hawks in the genus
Accipiter may take
reptiles from trees whilst other species may hunt them on the ground.
Snakes are the primary prey of the snake-eagles (
Circaetus ) and
Dryotriorchis ). Apparently, the
mammal-hunting, huge and endangered
Philippine eagle (Pithecophaga
jefferyi) is most closely related to the snake eagles. Another
handsome aberration of the snake-eagle lineage (although, unlike the
Philippine, has long been known to be a snake-eagle) is the bateleur
Terathopius ecaudatus), which has evolved unusually bright plumage in
adults, with a huge red cere, red feet, bright yellow bill, and boldly
contrasting grey-and-white markings over black plumage. The bateleur
has specialized to feed extensively on carrion and almost any other
feeding opportunity that presents itself.
REPRODUCTIVE BIOLOGY AND POPULATIONS
In terms of their reproductive biology and socio-sexual behavior,
accipitrids share many characteristics with other extant groups of
birds that appear not be directly related, but all of which have
evolved to become active predators of other warm-blooded creatures.
Some of the characteristics shared with these other groups, including
falcons , owls , skuas and shrikes , are that the female is typically
larger than the male, extreme devotion for breeding pairs to each
other and often to a dedicated nesting site, strict and often
ferocious territorial behavior, and, on hatching, occasional
competition amongst nestlings, including regular siblicide in several
Before the onset of the nesting season, adult accipitrids often
devote a majority of their time to excluding other members of their
own species and even of other species from their nesting territories.
In several species, this occurs by territorial display flights over
the border of their breeding ranges. In several forest dwelling
varieties, however, vocalizations are used to establish territories.
Due to the density of the habitat, display flights are apparently
While a single devoted breeding pair is considered typical, research
has revealed that in varied accipitrids, multiple birds engaging in
nesting behavior is more commonly than previously thought. Some
harriers have evolved to become polgynous, with a single smaller male
breeding with and then helping multiple females raise young. The most
extreme known species of accipitrid in terms of sociality is the
Harris\'s hawks (
Parabuteo unicinctus), which up to seven fully-grown
birds may hunt, nest and brood cooperatively, with the additional
birds typically being prior years' offspring of the two most mature
Unlike the other two larger groups of raptorial birds, the owls and
most falcons, accipitrids typically build their own nest. Nest sites
are typically in relatively secure places, such as the crook of a
large tree or an ample cliff ledge, and can vary in elevation from the
flat ground of prairies or steppe to near the peaks of the tallest
mountains such as the
Himalayas . Accipitrids will readily return to
use a nest site repeatedly, which has resulted in several of the
largest bird's nests known, as a single nest may see decades of use,
with more material added each breeding season. The single largest
known tree nest known for any animal, belong to a bald eagle
Haliaeetus leucocephalus), was found to be 6.1 m (20 ft) deep, 2.9
meters (9.5 ft) across, and to weigh 3 short tons (2.7 metric tons).
Some species, especially eagles, will build multiple nests for use in
alternating years. Although they usually use nests they build
themselves, accipitrids sometimes use abandoned nests build by other
animals or pirate nests from other birds, typically other types of
Compared to most other types of birds, the stretch from egg-laying to
independence in young birds is very prolonged. In accipitrids, the
breeding season ranges from about two to three months to roughly a
year and a half, the latter in some of the larger tropical eagles.
Species inhabiting temperate ranges as a rule have shorter breeding
seasons due to the shorter stretches of warm weather that facilitates
ready capture of prey.
Usually from 2 to 6 eggs are laid in accipitrids, a relatively small
clutch, and some species may lay only one egg. In almost all
accipitrids, eggs are laid at intervals rather than all at once and in
some larger species the intervals can be several days. This results in
one of the hatchlings being larger and more advanced in development
than its siblings. The benefits of siblicide, which is at least
occasionally recorded in many species and almost always occurs in
some, such as tropical members of the booted eagle group, is that the
smaller siblings are a kind of insurance policy that if the oldest,
strongest nestling dies, one of the smaller siblings may take its
place. In most species that have displayed siblicide, times of food
plenty may result in two or more the nestlings being successfully
raised to fledging.
In most accipitrids, the smaller males typically attain food both for
the incubating and brooding female and the nestlings. Males, however,
occasionally take a shift incubating or even more sporadically of
brooding of the nestlings, which allows the female to hunt. Most
accipitrids feed their nestlings by feeding them strips of meat or
whole prey items, but most vultures feed their nestlings via
Fledgling often takes considerable effort for young birds and may
take several weeks as opposed to days in many other types of birds.
Once independent of their parents, young accipitrids often most wander
for considerable stretches of time, ranging from 1 to 5 years before
they attain maturity. Most accipitrids have distinct plumages in their
immature stage, which presumably serves as a visual cue to others of
their species and may allow them to avoid territorial fights. Shortly
after attaining mature plumages, pairs form with a male typically
displaying, often in flight but sometimes vocally, to win over a
female. Many accipitrids breed with the same mate for several years or
for life, although this is not the case for all species and, if a mate
dies, the widowed bird will typically try to find another mate the
following breeding season.
* SUBFAMILY ELANINAE – elanine kites (6 species)
Genus Macheiramphus (was doubtfully placed, moved from
* SUBFAMILY PERNINAE – honey buzzards (c.15 species)
* SUBFAMILY AEGYPIINAE –
Old World vultures
* SUBFAMILY GYPAETINAE
* SUBFAMILY BUTEONINAE – buteonine hawks, true eagles and
sea-eagles (c.100 living species, probably poly- or paraphyletic )
Buteo (probably paraphyletic , might include
part and Parabuteo)
Rupornis – roadside hawk
Morphnarchus – barred hawk
Buteogallus (probably paraphyletic , might include
Leucopternis in par
Leucopternis (probably polyphyletic )
Cryptoleucopteryx – plumbeous hawk
* SUBFAMILY AQUILINAE
Lophaetus (possibly junior synonym of Ictinaetus)
* SUBFAMILY CIRCINAE – harriers (some 16 living species)
* SUBFAMILY POLYBOROIDINAE – harrier hawks
* SUBFAMILY MILVINAE – milvine kites (some 14 species)
Helicolestes – formerly included in Rostrhamus
* SUBFAMILY ACCIPITRINAE – goshawks, sparrowhawks, and relatives
(c.55 living species)
* SUBFAMILY CIRCAETINAE – snake eagles (about one dozen species)
* SUBFAMILY HALIAEETINAE – sea eagles
* SUBFAMILY HARPIINAE
* SUBFAMILY MELIERAXINAE – chanting goshawks
Neophrontops americanus fossil
Neogyps errans fossil
As 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
* Milvoides (Late
Eocene of England)
* Aquilavus (Late Eocene/
Early Oligocene – Early Miocene of
* Palaeocircus (Late Eocene/
Early Oligocene of France)
* Palaeastur (Agate
Fossil Beds Early Miocene of Sioux County, USA)
Pengana (Early Miocene of Riversleigh, Australia)
* Promilio (Agate
Fossil Beds Early Miocene of Sioux County, USA)
* Proictinia (Early – Late Miocene/Early Pliocene of C and SE USA)
Neophrontops (Early/middle Miocene – Late Pleistocene) –
formerly in Neophron
* Mioaegypius (Xiacaowan middle Miocene of Sihong, China)
Apatosagittarius (Late Miocene of Nebraska, USA)
* Gansugyps (Liushu Late Miocene of China)
* Palaeoborus (Miocene)
* Qiluornis (Miocene of Shandong, China)
* Thegornis (Miocene of Argentina)
* Garganoaetus (Early Pliocene of Gargano Peninsula, Italy)
Amplibuteo (Late Pliocene of Peru – Late Pleistocene of S North
America and Cuba) – may belong to extant genus Harpyhaliaetus
* Palaeohierax – includes "Aquila" gervaisii
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
Accipitridae gen. et sp. indet. (Huerfano Early
Eocene of Huerfano
Accipitridae gen. et sp. indet. (Borgloon
Early Oligocene of
Accipitridae gen. et sp. indet. (Bathans Early/Middle Miocene of
Otago, New Zealand)
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?
Accipitridae gen. et sp. indet. (Late Pliocene/Early Pleistocene
of Ibiza, Mediterranean) – Buteo?
Accipitridae gen. et sp. indet. (Egypt)
AMNH FR 2941, a left coracoid from the Late
Manha Formation of Chimney Butte (
Inner Mongolia ) was initially
assessed as a basal mid-sized "buteonine"; it is today considered to
be more likely to belong in the
Gruiformes genus Eogrus . The Early
Cruschedula was formerly thought to belong to
Spheniscidae , however reexamination of the holotype in 1943 resulted
in the genus being placed in Accipitridae. Further examination in
1980 resulted in placement as Aves incertae sedis.
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