Brown Snake Eagle (Circaetus cinereus) – Planet of Birds

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Aug 27 2011

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Brown Snake Eagle (Circaetus cinereus)

Brown Snake Eagle

[order] ACCIPITRIFORMES | [family] Accipitridae | [latin] Circaetus cinereus | [authority] Vieillot, 1818 | [UK] Brown Snake Eagle | [FR] Circaete brun | [DE] Einfarb-Schlangenadler | [ES] Aguila Culebrera Sombria | [NL] Bruine Slangenarend

Subspecies

Genus Species subspecies Region Range
Circaetus cinereus AF widespread

Genus

Members of the genus Circaetus are the snake eagles. They form a monophyletic group Circatinae that is sister to the Old World vulture group, Aegypiinae. These are mainly birds which specialise in feeding on snakes and other reptiles, which is the reason most are named as “snake-eagles” or “serpent-eagles”. They are restricted to warmer parts of the Old World. They have hooked beaks for tearing flesh from their prey, strong legs and powerful talons. They also have extremely keen eyesight to enable them to spot potential prey from a distance.

Physical charateristics

The adult is uniformly dark brown. Some individuals have a narrow black line above and below the eyes. The tail is dark brown with three narrow grey bars and a whitish tip. The flight feathers are dark brown above, becoming paler and mottled towards the base of the inner web. Below, it is entirely brown. The under-side of the flight feathers is pale grey. The eyes are bright yellow, the cere, legs and feet pale grey white. The bill and claws are black. The immature is very much like the adult, albeit a little paler, with varying amounts of white feather bases showing on nape and belly, and paler edges to the feathers of the back. The cheeks and head are greyer than in the adult. The young start life with a covering of pure white down. Their eyes are grey at first, becoming pale yellow. Their cere and legs are almost white, and their bill pale grey.


wingspan min.: 160 cm wingspan max.: 170 cm
size min.: 70 cm size max.: 80 cm
incubation min.: 47 days incubation max.: 53 days
fledging min.: 95 days fledging max.: 105 days
broods: 1   eggs min.: 1  
      eggs max.: 1  

Range

Africa : widespread. The Brown Harrier can be found in lightly and moderately wooded parts of Africa south of the Sahara. It is not common in open plains. It is especially numerous in thorn bush in East and north-east Africa.

Habitat

Throughout its range, this is a bird of dense savannah, and of thorn bush veld. It is only rarely found in grass plains, and never in forest country except where it has been cleared for cultivation, where it can often be seen sitting on dead trees.

Reproduction

In display it soars high over its breeding area, making frequent loud display calls. No aerobatics are performed, and the display is usually by a single bird.
Nests are small structures, usually placed on top of thorny Acacias, or tree Euphorbia. They are about three feet across by six inches deep, made of small sticks, lined with a few green leaves. They are usually well hidden in masses of creepers. The same nest is not normally used in successive years, but the birds may return to the same tree and rebuild after a period of years.
The female lays one egg only. It is large, round, white and usually unmarked. Incubation is carried out by the female only. She sits very tightly and so flat in the nest on the approach of an intruder that she is almost invisible. She is fed on the nest by the male, who seldom appears in the vicinity of the nest site and does not roost anywhere near. The incubation period is about 45 days. Laying dates vary by location and egg-laying is not confined to the dry season.
Hatching takes about two-and-a-half days, and the female may help the eaglet out of the shell. At this point the nestling weighs about 100 grams, and has partly closed eyes. The eye, legs, bill and feet darken or change colour during the fledging period; the eye becomes yellow between 21 and 29 days, but remains paler than that of the adult. At about 21 days the first feathers on the back push through the down, and by 36 days the front part of the body and the wings are feathered. The rump and flanks are still downy, and the tail is very slow to develop. The young can pull a snake from the parent’s crop at nineteen days, can stand at 35 days, and can feed itself a couple of days later, when it is still partly downy. Parental care is confined to the period when the young is more or less helpless in the nest, and at this later stage it is left alone in the nest, where it is much less active than most young eagles. It will make a begging call either to its parents or to any other raptors overhead. Both sexes bring food, but visits are brief and they neither roost nor spend much of the day near the nest.
When a snake is brought the method of delivery to the young, or of drawing it out of the adult’s crop, is similar to that described under the Short-toed Eagle, the parent pulling the snake out itself with its foot, or the young seizing the end and assisting as the adult strains back. Large snakes up to five feet long are brought to the young, including venomous species, such as cobras and boomslang.
The fledging period is long, often over 100 days, and the young does not practise wing-flapping until a few days before leaving the nest. When it makes its first flight, its plumage is much more nearly mature than is the case with many other young eagles, and its weight will be about 2,100 grams. After leaving the nest the young does not remain long in the vicinity, but apparently accompanies its parents to wherever they may be, returning only sporadically to perch near the nest in their company.

Feeding habits

The diet of the Brown Harrier is about 70% snakes, including poisonous species such as large cobras. The remaining 30% is made up mostly of game birds, and occasionally poultry. Mammals are taken rarely, if at all. The prey is always taken on the ground, frequently by dropping on it from a perch.

Video Brown Snake Eagle

httpv://www.youtube.com/watch?v=unmLgItEGjA

copyright: Juan Sanabria


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). The population trend appears to be stable, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size may be moderately small to large, 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.
Brown Snake Eagle status Least Concern

Migration

It is non-migratory throughout its range, except in Senegal, where it breeds early in the year and leaves after the breeding season.

Distribution map

Brown Snake Eagle distribution range map

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