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Aug 27 2011

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Crowned Eagle (Stephanoaetus coronatus)

Crowned Eagle

[order] ACCIPITRIFORMES | [family] Accipitridae | [latin] Stephanoaetus coronatus | [authority] Linnaeus, 1766 | [UK] Crowned Eagle | [FR] Aigle couronne | [DE] Kronenadler | [ES] Aguila Coronada | [NL] Kroonarend

Subspecies

Monotypic species

Genus

Members of the Stephanoaetus genus are very large, very powerfully built eagles with a full, divided crest. They have short and rounded wings, and a long and broad tail. The bill is quite compressed. Their legs are heavy, feathered, with short and heavy toes and very large talons. The genus contains only one species, S. coronatus in African forests. This bird is very closely related to the Spizaetus genus (Hawk-Eagles), of which it is a specialized offshoot.

Physical charateristics

The Crowned Eagle has dark grey upperparts with rufous and white below; its belly and breasts are heavily mottled with black. This eagle has relatively short, broad and rounded wings for added manoeuvrability in its environment. The rufous underwing coverts and strongly barred white and 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. 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 and spotted thighs. The legs are extremely powerful and the eagle possesses formidably large, strong talons, often used for killing and dismembering prey. Length is 80-99 cm (31-39 in), the wingspan is 1.51-1.81 m (5.0-5.9 ft) and weight is 2.55-4.7 kg (5 lb 10 oz-10 lb 6 oz).[4][5] As in most birds of prey, the female is larger than the male (by 10-15%).

Listen to the sound of Crowned Eagle

[audio:http://www.planetofbirds.com/MASTER/ACCIPITRIFORMES/Accipitridae/sounds/Crowned Eagle.mp3]

Copyright remark: Most sounds derived from xeno-canto


wingspan min.: 150 cm wingspan max.: 180 cm
size min.: 80 cm size max.: 99 cm
incubation min.: 45 days incubation max.: 55 days
fledging min.: 110 days fledging max.: 130 days
broods: 1   eggs min.: 1  
      eggs max.: 2  

Range

Africa : West, Central, East, Southeast

Habitat

This magnificent bird is thought by some to be the finest of all African birds of prey, and possibly the most powerful, although not the largest. It can be found in forests or on rocky hills supporting small patches of forest. It rarely wanders into the savannah or bushlands surrounding these hills, but may occasionally be found right outside its normal haunts in, for instance, riverine Acacia forest strips or rather open woodland. It is normally sedentary and attached to the same area most of the year, but there is some evidence that the birds occasionally move some distance, as they must when changes of mates occur in isolated breeding sites.

Reproduction

The male displays constantly over the haunts of a pair, usually near the nest site, but also around the periphery of the home range. The display consists of a series of steep dives and ascents, with a few wing flaps at the top of each climb, and describing circles and fgures of eight. It is usually performed at a great height, as much as 3,000 feet above the forest. At the top of each ascent the head is thrown back slightly and the display call pours out in bursts of up to 30 seconds, interspersed with periods of silence. The female performs a similar display, less often, and with a mellower voice. The pair also perform striking mutual displays, sometimes arising from the first type, or sometimes starting when a soaring pair come together. The male dives towards the female who turns on her back and presents her talons to his; this may be repeated five or six times before the pair break off. Copulation takes place on the nest, may occur several times in a day, and as much as a year prior to egg-laying. A pre-copulation display by the male consists of running round the crouching female, with wings upraised to display the striking chestnut under-wing coverts and the beautiful barring.
A pair usually has only one nest, built in a large forest tree, very often in a river valley, and generally in a shady main fork of the tree at any height from 40 to 150 feet above ground. It is built of large sticks lined with green branches and is used year after year for many years by a succession of different birds. Both birds build, but the female brings more material than the male; when both are building together the female may remain in the nest while the male goes to and fro. The female will then continue to build after the male has gone. A new nest takes four to five months to construct, and nest repair prior to laying may take one to three months, according to the amount of material brought. In time the nest becomes very large and heavy. A new one may be five feet across by three feet thick, but old nests may be eight to ten feet deep and six to eight feet across, with a depression about three feet across in the centre, thickly lined with green sprays. The sticks and green branches are usually collected from quite close to the nest site. Green branches are torn off and carried in the bill, and larger sticks in the feet. Nests of adjacent pairs are usually three to four miles apart.
One or two eggs are laid, the timing varying across the species’ extensive range, although between July and October is most common. The breeding season extends through both wet and dry periods in some areas. The presence of a large eaglet in the nest is not a sure guide to egg-laying dates, since the young eagle is fed at the nest for up to eleven months after its first flight. When a natural disaster befalls the clutch a replacement clutch may be laid, sometimes up to two months later.
Incubation is by both sexes, although the female always takes the greater share, sitting at night, and performing 80-90% of the incubation. During the incubation period the male brings prey to the nest. Males have been known to feed on prey brought by females, and when feeding a female who sits persistently the male brings a kill once every three to five days. The incubation period is 49 days.
The young eaglet is quiet when first hatched, but soon becomes active. It is very precocious for an eaglet, and can feed itself while still entirely downy. As is common among larger eagles, when two young hatch they engage in a `Cain and Abel’ struggle and one succumbs (generally the fist hto hatch, as it will have a head start of a few days on its sibling. The first feathers appear through the down at about 40 days, and feathers cover the down by 76 days ; the crest appears at about 60 days. After 76 days the main feather development is in the tail and wing quills. The rear talon grows faster than the others and the eaglet often falls over through catching it up in the sticks of the nest. From 40 days onward the eaglet can feed itself on prey brought by a parent, but does not always do so. Wing-flapping exercises begin from 45 to 50 days and increase in intensity from 75 days onwards, stimulated by winds. Before taking their first flights some eaglets, especially males, climb about on the branches of the nest tree and jump from bough to bough; others, females, are more sluggish, and make their first flight without preliminary exercises of this sort. The fledging period is 103-115 days.
Eaglets can be sexed wit a fair degree of accuracy by their size and degree of activity at the end of the fledging period, the more active males making their first flight five to seven days before females. The sex ratio at fledging is about equal. When made, the first flight carries the young one 50-300 yards, and is made at any time of the day, usually in the absence of the parents, and without any coaxing by them. After making its first flight the young bird will probably return to roost in the nest.
Both parents brood the young, but the female much more than the male, and often exclusively. Pairs vary greatly in behaviour. Immediately after the hatch the male doubles his rate of killing from one kill per three days to one per one-and-a-half days; this cannot be controlled by his own appetite, which appears to dictate killing rates at other times. The female plays the major part in brooding and tending the chick up to about day 60, but from 60 to 110 days she is released from duties at the nest by the rapid development of the eaglet, and thereafter brings more prey than does the male.
In the early fledging period the chick is closely brooded, and the female remains on or near the nest for 95% of the day, and may brood as much as 75-80% of the time, brooding decreasing day by day. Brooding by day ceases after about 42 days, by which time the eaglet’s first feathers have appeared. Thereafter parental time at the nest is sharply reduced, but the female remains near the nest, bringing many green branches, and is then liable to be very aggressive to an intruder.
The male may spend much time in the vicinity of the nest, perching on trees, but is more likely to appear only when he brings prey. The female roosts in the vicinity, or in the nest tree itself, until the eaglet is well feathered, but males do not as a rule roost near the nest. There is much variation from pair to pair in these various habits, but in general the behaviour of the parents is correlated with the stages of the eaglet’s development; once it is well feathered it is left very largely alone by day and night, except for brief visits with food. The feeding rate is reduced to about one kill per two days at the end of the fledging period, but there is no conscious starvation of the young to induce it to fly.
After fledging, the young remains in the neighbourhood of the nest, and is fed in it by either parent at intervals of three to five days for 270-350 days after it makes its first flight. During this time it is known to kill for itself, the earliest record of a kill by a young eagle being at day 61 of the post-fledging period. It nevertheless continues to solicit any adult in the neighbourhood, whether or not it has prey. When the adult brings prey it calls with increasing frequency and intensity as it approaches the nest, and the young eagle is attracted to the nest to receive the kill. It will not normally take the kill except at the nest. During this protracted period of dependence the young bird gradually grows stronger and makes longer flights, but seldom soars to any height until about to become independent. Final independence is apparently due to increasing indifference to the food-bringing parent by the young; when a calling parent with food is ignored by the young it may take the prey away again or leave it in the nest, but repetition of such incidents seems to bring about the final break. The feeding rate throughout this period varies greatly from several kills brought in a day to starvation for up to thirteen days; protracted periods of starvation may stimulate the young eagle to kill for itself, but there is also some evidence that more food is brought by the parents just before the end of the post-fledging period. The biological advantage of this very long period, which results in a breeding cycle of more than 500 days and prevents annual breeding, may be to produce an unusually strong young eagle better able to survive to maturity.
This species breeds regularly every two years, except in a few instances. Almost all young that leave the nest also reach independence. There may be heavy mortality after independence from the parents as sub-adult immatures are rarely seen.

Feeding habits

The hunting range of a pair of Crowned Eagles is normally four to ten square miles of forest country, or a smaller area of rocky hills and cliffs where hyrax exist in large numbers. Inside the forest the birds are seldom seen, but may be found perched on a commanding tree overlooking a glade or water-hole, especially in early morning and evening. They also spend much time soaring over the forest, when there is invariably an outcry from monkeys feeding in the tree-tops. Most of the hunting is done by dropping on prey from a perch, and when hunting the eagle is able to fly silently and dexterously from perch to perch. It kills much of its prey on the forest floor, but will catch monkeys and probably hyrax in the tree-tops. Having killed on the ground, it has the ability to fly almost vertically upwards to a branch before feeding, although it will sometimes tear up prey on the ground. Both sexes feed on each other’s kills, and a good-sized animal will be killed every three or four days. The eagles start to hunt soon after dawn, and the majority of kills are made early in the morning or late in the evening, though sometimes they are made late in the day as well.
Were it not for the fact that this is an exceedingly noisy bird, constantly drawing attention to itself in aerial display or calling when it is hidden inside a big forest tree, it would be seldom noticed. It is, however, commoner and more widespread than is generally supposed, and is found in almost any patch of forest in East Africa, even in quite heavily populated country. It is rarer further south, where it has been persecuted, and seems to be rare, too, in the forests of Ethiopia at the northern fringe of its range.

Video Crowned Eagle

httpv://www.youtube.com/watch?v=8oWLHbBc9WQ

copyright: J. del Hoyo


Conservation

This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). Despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size may be small, but it is not believed to approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
Crowned Eagle status Least Concern

Migration

Adults are sedentary, but juveniles disperse from breeding areas

Distribution map

Crowned Eagle distribution range map

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