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.
|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|
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.
Video Brown Snake Eagle
copyright: Juan Sanabria