Crowned Eagle
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| Stephanoaetus coronatus (Linnaeus, 1766) |
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 Crowned Eagle range
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The Crowned Eagle (Stephanoaetus coronatus), more precisely known as the Crowned Hawk-eagle, is a very large, powerful, crested bird of prey (80-90 cm approx) found in tropical Africa south of the Sahara; in Southern Africa a common resident in suitable habitat in the eastern areas.
It inhabits mainly dense forests; its staple diet consists of monkeys (particularly those of the genus Chlorocebus) and other mammals up to 20 kg (44 lb), such as the Cape Hyrax and small antelopes. To a far lesser extent, birds and monitor lizards are also taken, however 98% of the diet is mammalian.
While smaller than the Martial Eagle, the Crowned Eagle is renowned as Africa's most powerful and ferocious eagle in terms of the weight and nature of prey taken. Due to their striking similarities, the Crowned Eagle is often considered Africa's analogue of the Harpy Eagle.
The Crowned Hawk-eagle is the only extant member of the genus Stephanoaetus. A second species, the Madagascar Crowned Hawk-eagle (Stephanoaetus mahery) became extinct after humans settled on Madagascar (Goodman, 1994). It was the largest and strongest bird of prey of prehistoric Madagascar (see Elephant Bird) and together with the living Fossa (animal) Cryptoprocta ferox, the larger Giant Fossa Cryptoprocta spelea (Goodman et al. 2004) and the two malagasy crocodiles, the living Nile crocodile and the recently extinct giant dwarf crocodile Crocodylus robustus the apex predators on the island. Extinction by overhunting of the giant lemurs which constituted its main prey seems to have been the main reason for this species' disappearance, which took place at some time during the second half of the first millennium AD.
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[edit] Description
Dark grey upperparts with rufous/white below, belly and breasts are heavily mottled with black. This eagle has short, broad and rounded wings for added maneuverability in its environment. The rufous underwing coverts, strongly barred white/black outer wings and tail are all diagnostic in flight. The large crest (often raised), combined with this bird's very large size make the adult near-unmistakable at suitable range.
However, the juvenile is often confused with the juvenile Martial Eagle, especially in flight. The juvenile Crowned is distinguished from that species in having a much longer, more heavily barred tail, spotted legs and an all-white head.
As with most large eagles, the female is larger than the male. The legs are also extremely powerful and the Eagle possesses formidably large, strong talons, often used for killing and dismembering prey. Length: 80-90cm (32-36"). Wingspan: 1.5-2.1m (~ 5-7 ft). Weight 3.5-5.5kg (~ 8-12lb).
[edit] Distribution and habitat
In Eastern Africa, the Crowned Eagles's range extends from southern Uganda and Kenya, forested parts of Tanzania, eastern Zambia, the Democratic Republic of Congo, Malawi, Zimbabwe, Mozambique, Swaziland and eastern South Africa about as far south as Knysna.
Its range also extends westward about as far as Liberia, though its distribution is severely fragmented in these areas. The eagle is less prominent at the extremes of its range, being most populous between Zimbabwe and Tanzania; it is, however, restricted to denser vegetation and indigenous forests throughout its distribution.
The Crowned Eagle inhabits dense indigenous and riverine forests (sometimes plantations), heavily wooded hillsides, dense woodland and rocky outcrops throughout its range, at an altitude of up to 11,000 ft. Owing to lack of suitable habitat (through deforestation and industrialisation), the eagle's range is discontinuous.
[edit] Ecology
The Crowned Eagle is a non-migratory Eagle and is largely sedentary, usually inhabiting a fixed territory for most of its lifespan. There is evidence, however, that the birds migrate moderate distances when circumstances require it, for example when changing mates in isolated breeding areas (The Hawk Conservancy Trust, 2006). However, such migration is local in scale and is not comparable to the seasonal migrations of some other Eagle species (e.g. the Steppe Eagle.)
Whilst quintessentially an elusive species (owing mostly to its habitat), the Crowned Eagle is highly vocal and is renowned for its noisy, undulating display flight. The male performs an elaborate rise-and-fall display over the forest canopy both during the breeding season and outside it as a territorial proposition. During this display, the male is extraordinarily noisy and may reach heights exceeding 900m (~ 3000 ft). The voice is a series of loud whistles that rise and fall in pitch. The female may also perform independent display flights and pairs are also known to collaborate in spectacular tandems.
[edit] Diet
The Crowned Eagle's staple diet is 98% mammallian, with Vervet monkeys (amongst other smaller primates) being favorites. In suitable habitat the Eagle will also take Hyraxes and small Antelope such as Duiker. Prey weighing up to 20kg (44 lb) has been recorded. Quintessentially, an adult Crowned Eagle will only resort to hunting large wild fowls (such as Guineafowl), Monitor lizards and snakes when mammalian food sources are scarce, though this is uncommon. Juveniles and subadults, however, may take these lines of prey more frequently.
Being a forest-dwelling species, the Crowned Eagle has no need to travel great distances to hunt, nor employ a great deal of active hunting flight (such as soaring seen in Savanna-dwelling species). Rather, the Crowned Eagle tends to hunt passively; a soaring range of 4-10 miles is the norm and is only seldom exceeded. After flying above the canopy and locating a suitable hunting spot (sometimes by the call of the noisy Vervet monkey), the Eagle will wait on a perch, perhaps for a nearby troop of monkeys to be spotted. Following the sighting of suitable prey, the Eagle quickly and stealthily maneuvers itself through the forest towards its prey, a certain element of surprise inherent in its final approach. The sharp, powerful talons may produce sufficient force to kill the prey on impact; if not, death from trauma or asphyxiation soon follows. Typically, the eagle can carry a mass roughly equal to its own (~ 3-6 kg) to its nest/perch; anything heavier is dismembered and returned to the nest/perch in pieces. Parts of larger prey are often cached for later consumption.
[edit] Breeding
Crowned Eagle pairs breed once every two years; a single breeding cycle is of approximately 500 days in duration.
The pair collaborate in building a massive nest in a fork of a large forest tree, typically 15–40 m (50–140 ft) above the ground. A nest built from scratch may take several (up to 5) months to construct, however existing nests are often repaired and re-used during successive breeding seasons. A larger nest may measure up to 2.5 m (8 ft) across and up to 3 m (10 ft) deep and consists of both dead and greener branches.
[edit] Conservation status
The Crowned Eagle is fairly common in suitable habitat, though its numbers show decline in sync with deforestation. It is far more common in protected areas and reserves than elsewhere in its range, though is still recorded consistently outside of these areas. Its numbers are probably higher than modern suspicion might suggest, though invariably hinge on rates of deforestation, especially in the north of its range.
Like the slightly larger Martial Eagle, the Crowned has throughout modern history been the target of gun-wielding farmers, who hold that the bird is a threat to their livestock [1]. Such beliefs are erroneous; neither the Crowned nor the Martial have been implicated in regular attacks on livestock, with only isolated cases of starving individuals attacking calves. It is worth noting that the Crowned in particular rarely leaves the forest to hunt, and occasions where it soars outside of dense forest are usually owing to territorial or breeding-related behavior.
[edit] Trivia
In April 1996 the world's first captive born Crowned Eagle hatched at The San Diego Zoo.
Part of the skull of a human baby was once found in the nest of a Crowned Eagle, presumably because the baby was of similar size to its other primate prey and thus a perfectly applicable food item for the bird, though this is the only record of its kind.
[edit] References
- BirdLife International (2004). Stephanoaetus coronatus. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 08 May 2006. Database entry includes justification for why this species is of least concern
- Gibbon, Guy; Maclean, Gordon & van der Merve, Steven (1997): Roberts' Multimedia Birds of Southern Africa 2.1 (CD-ROM). Southern African Birding cc.
- The Hawk Conservancy Trust (2006): Crowned Eagle - Stephanoaetus coronatus. Retrieved 2006-OCT-7.
- Goodman, Steven M. (1994). Description of a new species of subfossil eagle from Madagascar: Stephanoaetus (Aves: Falconiformes) from the deposits of Ampasambazimba. Proceedings of the Biological Society of Washington, 107: 421-428.
- Goodman S. M., Rasoloarison R. M. and Ganzhorn J. U. (2004). On the specific identification of subfossil Cryptoprocta (Mammalia, Carnivora) from Madagascar. Zoosystema 26 (1): 129-143.
