a web page by Don Roberson |
HAWKS & EAGLES Accipitridae |
||||||
|
||||||
|
||||||
|
||||||
For decades I've judged the Great Philippine Eagle
as the world's "best bird" (see my photo collage below that combines an
in-the-field flight shot superimposed on the forest background taken at
the same location). The world's "best bird" is now critically
endangered in its remote Philippine forested refuge. |
||||||
 |
||||||
| Such large eagles take years to reach maturity. In the tropical African savanna, Martial Eagle shows a very pale to white juvenal plumage (below left) but becomes entirely dark-headed as an adult (below right). Likewise, along Africa's rivers and lakeshore, a juvenile African Fish-Eagle (second row, left) looks quite different than the familiar adults (second row, right). | ||||||
|
||||||
|
||||||
 |
||||||
Another impressive eagle is Chaco Eagle of open woodland in central South America (above). It is now placed in genus Buteogallus, as is Solitary Eagle B. solitarius and Savanna Hawk B. meridionalis, and such well-known Buteogallus species as Common Black Hawk B. anthracinus and Great Black Hawk B. urubitinga. I often think of these latter Buteogallus hawks as specialists in feeding along streams or estuary edges, eating amphibians (especially frogs), crabs and freshwater crayfish. Meanwhile, down under in the southern hemisphere in Australia, the largest predator bird is Wedge-tailed Eagle (below left), with the moon setting behind it. It is widespread throughout the interior of Australia
|
||||||
|
||||||
|
||||||
A distinctive and spectacular Old World vulture is Bearded Vulture, often called Lammergeyer
(below in flight high over the Tibetan plateau). Bearded Vulture is a
signature icon of crags in remote mountain wilderness in Eurasia and
Africa. They even reside at at altitudes of 7500 m (24,600 ft) on Mount
Everest. |
||||||
 |
||||||
In contrast, Palm-nut Vulture (left) of sub-Saharan Africa feeds mainly on the fleshy fruit-husks of the oil-palm (Elaeis sp.) and the fruits of raphia-palm Raphia australis. Its distribution matches the distribution of these palms, and it is most common in coastal forests and mangrove swamps below 1500 m., although it does wander widely across the African savannas. The huge eagles and Old World vultures are certainly of interest, but the bulk of the Accipitridae are the smaller hawks, buzzards, hawk-eagles, serpent-eagles, harriers, kites and relatives, to which we now turn. |
||||||
 In
much of the world, and especially the temperate zones, the basic "hawk"
(often called "buzzard" in the Old World) belongs to the genus Buteo or Butastur.
Some 32 species are distributed across the largest continents,
Caribbean islands and Madagascar, and to the Galapagos and Hawaii. In
much of east Africa that species is Augur Buzzard (right). In California where I live our usual hawk — the default i.d. for any large soaring raptor — is the Red-tailed Hawk
(both photos below of the same nest). This nesting pair were raising
two chicks but had to suffer attacks from an aggressive Northern
Mockingbird disturbed by the presence. The mimid's concern seems
unwarranted as Red-tailed Hawk eats small mammals and snakes. As in
many Buteos, the Red-tail comes in a bewildering variety of plumages
and color morphs, the whole spectrum of which cannot be shown in any
literature. One learns to use shape, size and behavior. |
||||||
|
||||||
| Buteonine raptors vary from resident species to long-distance migrants. Grasshopper Buzzard (below right) ranges across the Sahel zone of sub-Saharan Africa but its movements are affected by prey changes in the continuum of wet-dry seasonality. It often follows the tracks of fires, eating grasshoppers and other insects flushed around the burning edges. The Arctic breeding Rough-legged Hawk (below center) is a long-distance migrants. Regular in winter in the interior of North America, during "invasion years" immatures (like this one) may turn up hundreds of miles farther south. Two temperate North American species — Broad-winged Hawk from the the east and Swainson's Hawk from the west — migrate in incredible numbers, circling in huge "kettles" on rising thermals for long distances. A Broad-winged Hawk is diving on a Swainson's Hawk in this photo from east Texas (below right). These two raptors are the fundamental core of New World hawk-watching. Numerous hawk-watching atop mountains or ridges dot North America [some great eastern U.S. sites were outlined in Heintzelman (1976); an impressive California site at Pt. Diablo, Marin Co., is detailed in Binford (1979)]. Migrant Swainson's Hawks in spring and fall form the "river of hawks" at sites from southern Mexico to Panama. Raptor migration can be just as impressive in the Old World, at places like Falsterbo, Sweden; the Bosporus, Turkey; and Eilat, Israel. There is even an important migration of Black Baza Aviceda leuphotes in southeast Asia. | ||||||
|
||||||
Some of the harriers show distinctive sexual dimorphism. The adult male Northern Harrier of North American is gray above and white below (below) while the females are mostly mottled brown and young harriers are buffy-orange below.
Many of the Owl World harriers are long-distance migrants from northern Eurasia to Africa or the Middle East, but there are also island residents such as Reunion Harrier C. mailliardi, found only on that island in the Indian Ocean. |
||||||
|
||||||
A variety of Neotropical kites take a variety of wild prey. Hook-billed Kite (female in flight, above) is widely distributed in South and Central America, north to the Rio Grande River in south Texas. It is unusual in its variation in bill size, which does not vary geographically but is bi modally distributed in many parts of the range. There are large-billed and small-billed individuals — large bills twice as big as small ones — in both sexes and all ages. This bill dimorphism is an evolutionary solution to their main food source, tree snails. The variation in bill sizes allows the Hook-billed Kite to feed on different species and sizes classes of snails (Schulenberg 2018). Snail Kite (an immature individual at right) is another specialist. In its Everglades range in Florida its dietary preferences run primarily to the apple snail Pomacea but, like Hook-billed Kite, its wide range goes to the Brazilian Pantanal, where this youngster was eating a freshwater crustacean. The four kites in genus Elanus are gray-and-white raptors on open country distributed across all the major continents. There are distinctive black patches on the wings of each species. They quarter low over grasslands in search of small rodents, and are beautiful in flight. Examples include White-tailed Kite of North America (below left) and Letter-winged Kite of the arid outback of Australia (below right). |
||||||
|
||||||
 |
||||||
There are a huge number of bird-eating hawks in the world, most of them in the genus Accipiter, with 45 species comprising about 18% of the family. Many species are rare or local; many are difficult to identify. In North America there are two widespread species, difficult to separate without practice. The one shown (above) is Cooper's Hawk (a very lucky shot of a preening juvenile). Many Accipiters fly through the forest in search of small avian prey; some even frequent bird-feeders. Identification of Accipiters can be difficult. In the past I found good starting points in Dunne, Sibley & Sutton (1988) and Kaufman (1990); see also Clark & Wheeler (1987) and Wheeler & Clark (1995) for North America; Porter et al. (1981) and Forman (1999) for Europe and the Middle East; and specialized articles such as Morris & Hawkins (1998) on Madagascar Accipiters. In the 20 years since I listed these references in the first version of this web page, the literature on raptor identification has become extensive and much more thorough. |
||||||
  A
set of very opportunistic hawks are the harrier-hawks of Africa and
Madagascar (two species; sometimes called Gymnogenes) and the Crane
Hawk of the Neotropics. Both the African Harrier-Hawk (near right) and the Crane Hawk
(far right) are mid-sized, lanky, long-legged raptors of open forests
that sport a short crest. The Harrier-Hawk is also bare-faced. Over the
years various authors have noted similarities in morphology and feeding
habitats between these widely separated species. Both prey upon small
mammals, frogs, lizards, bird nests, and insects, which are found by
climbing around on tree trunks and limbs, peering into crevices and
holes while hanging at odd angles. The Harrier-Hawk even has a
reversible intertarsal ("knee") joint which can bend backward, as well
as forward, enabling the bird to reach into deep holes to extract the
contents. For prey that would otherwise be inaccessible, they may hang
under branches, keeping balance with flapping wings, and grabbing
anything that they find. Hunting techniques include raids on colonies
of nesting weavers or oropendolas, taking eggs and nestlings.
Harrier-Hawk also eats oil palm fruit, fish, and carrion. Despite
multiple similarities, these are examples of convergent evolution and
are not closely related (Lerner & Mindell 2005). |
||||||
While reptiles comprise only a small portion of the prey among most hawks, some species specialize on snakes. These include three species of snake-eagle (Circaetus) in Africa, and six species of serpent-eagles (Spilornis) in Asia, plus the Congo Serpent-eagle Dryotriorchis spectabilis in the Congo Basin.
|
||||||
Ornate Hawk-Eagle (right, an immature bird) is widespread throughout the Neotropics but I've only encountered it this one time. White-rumped Hawk (just below) is little-known and mostly overlooked in its South American range.
And the lovely Long-tailed Hawk (below) is usually overlooked in the thick lowland forests that extend patchily from west Africa to the Congo Basin. Brown et al. (1982) called it "uncommon to rare but probably commoner than supposed as very difficult to observe." It has bright chestnut underparts and very long tail, and can be found by its vocalizations. It appears to specialize of squirrels. |
||||||
 |
||||||
Photos: The African Hawk-Eagle Aquila spilogaster was at Tarangire NP, Tanzania, on 9 June 2018. The near-adult Bald Eagle Haliaeetus leucocephalus was in Priest Valley, Monterey Co., CA, USA, on 2 May 2010. The adult Harpy Eagle Harpia harpyja was hunting in the Serra das Araras, Mato Grosso, Brazil, on 4 Aug 1999. Ian Merrill took the wonderful shot of Philippine Eagle Pithecophaga jefferyi on Mt. Katanglad, Mindanao, Philippines, in Feb 2006; my montage with flight shot was taken there in Feb 1990. The young Martial Eagle Polemaetus bellicosus was at Tarangire NP, Tanzania, on 9 June 2018, and the adult was near Brandvlei, South Africa, in July 2005. The young African Fish-Eagle Haliaeetus vocifer
was along the Tarangire River, Tanzania, on 9 June 2018; the adult in
flight was along the Okavango River, Botswana, in July 2005.
All photos © Don Roberson, except for the Philippine Eagle © Ian Merrill and used with permission; all rights reserved. Bibliographic note: Family book: Rating
Literature cited:
|
The
Accipitridae — the family of hawks, eagles, kites, harriers, and Old
World vultures — includes some of the world's most awe-inspiring birds.
The sizes of birds-of-prey range from the tiny Pearl Kite Gampsonyx swainsonii
of South America, at a maximum of 100 grams, to the largest Old World
vultures at up to 12.5 kg, some 12-and-half times larger (Thiollay
1994). There are large and impressive eagles on every wooded continent.
Two examples are African Hawk-Eagle of sub-Saharan Africa (above) and Bald Eagle
of North America (left). Among the most spectacular are those great
tropical eagles that subsist on arboreal mammals. In Africa,
Verraeaux's Eagle Aquila verreauxii makes a specialized living on hyraxes. The BBC series "The Life of Birds with David Attenborough" has incredible shots of Martial Eagles hunting monkeys. In the Neotropics there is Harpy Eagle
(below left); we'd unintentionally flushed this adult from its prey (a
forest deer) not far from a known nest. And in the Philippines, the
greatest of all eagles — the Great Philippine Eagle,
once called the "Monkey-eating Eagle" (below right in an outstanding
shot by Ian Merrill) — hunts the treetops for civets, colugos, flying
squirrels, and monitor lizards. 
I've
had the good fortune to have quality experiences with both a nesting
Harpy Eagle and a nesting Philippine Eagle. The story of seeing the
latter at its nest in the wild in February 1990, with more photos, 
There are huge eagles at high latitudes also. In far northeastern Asia, a large female Steller's Sea-Eagle
may be the world's heaviest eagle. These impressive giants winter south
to Japan. Our only encounter, though, was this vagrant in North
America: an adult that spent a couple of years near Juneau, Alaska. To
see it one had to charter a helicopter to fly over the glaciers in the
mountains behind town, and follow the Taku River, trying to spot it as
it sat atop a riverside conifer (below).
Another
impressive group is the Old World Vultures [New World vultures are only
distantly related to hawks, and are placed in their own Family.] Times
are changing for many Old World vultures. Several, such as White-backed Vulture
(right) and of sub-Saharan Africa (right), have joined the list of
critically endangered vultures that began with the large vultures of
India since 2000. The White-rumped Vulture of south
Asia (there are more than 50 gathered at the carcass shown below) was
estimated at several million in the 1980s. As of 2016, the global
population was estimated at less than 10,000 adults. These and other
Asian vultures have crashed due to renal failure caused by diclofenac
poisoning. Until banned recently, diclofenac was used in veterinary
care of the abundant cattle in south Asia. It wiped out 99% of the
world's population of White-rumped Vulture, Slender-billed Vulture Gyps tenuirostris, and Indian Vulture G. indicus,
as well as many Red-headed Vulture Sarcogyps calvus. In recent years,
the use of diclofenac, as well as the use of strychnine and other
poisons, in Africa has led to very serious declines in White-backed
Vulture, Rüppell's Vulture Gyps rueppelli, and
Lappet-faced Vulture. In Africa, cattle grazing has taken over much
formerly wild land in which African vultures would consume the
carcasses of kills from lions, leopards, and hyenas.The three photos
below illustrate vulture abundance in earlier times. One cannot now see
a gathering White-rumped Vultures in India as show in my 1978 shot: 
Today, congregations of African vultures are often limited to National Parks and preserves. This shot of a young Lappet-faced Vulture with its parent was at a nest in Tarangire NP, Tanzania. 
There are 16 species of harriers in genus Circus scattered throughout the world. Most hunt small mammals by quartering over marshes and wetlands on tilt-up wings. Spotted Harrier (right) of Australia can survive in the vast arid desert in the interior of the continent.
There
are almost 30 raptors in 18 genera that are called "kites." This is not
a natural groups but, rather, an assortment of mid-sized hawks, some of
which excel at 'kiting" — effortlessly soaring and gliding in thermals
in search of food —or gracefully "hanging in the air" by hovering.
Black Kites (Milvus migrans) and is widespread across
Eurasia and Africa, various considered either three species (Black
Kite, Yellow-billed Kite, Black-eared Kite) or one polymorphic and
variable species. Some populations are resident and otherwise
migratory. Many populations live commensally with humans, becoming a
very familiar species and heir angled wing and forked tail makes them
easy to identify. Global population estimates run up to 6 million
individuals. Unlike other kites, Black Kites are opportunistic hunters
and are more likely to scavenge. This "Black-eared" Blake Kite (left) is scavenging in a huge rubbish dump in eastern India. 
The photo (left) is Crested Serpent-Eagle, a widespread and rather noisy hawk of southern Asia. Representing the snake-eagles is this Beaudouin's Snake-Eagle from the Sahel region of west Africa (below): 
There
are many more hawks in this huge family but I can mention only so many
on this page. So we wrap up with mention of some of the shy,
hard-to-see forest hawks, like those in the genus Leucopternis of the New World tropics (I don't yet have a photo of any of them). I was, however, very happy to photograph these:
