Friday, September 9, 2011

Cainism amongst Eagles

Talking about eagles [SEE: previous blog entry] - some of these large raptors are prone to Cainism, also known as the Cain & Abel syndrome OR Siblicide, meaning that the older chick in a nest kills the younger within the first few days of hatching. So if you see a Black eagle circling, it has to be "a Cain"!

Like the Black eagle, a Tawny eagle chick also follows this pattern, as well as Crowned eagles, Augur buzzard chicks & sometimes, the older of 2 Jackal buzzard chicks may kill the younger, but not always.

So again, this Tawny eagle youngster can be called "Cain" - the oldest of 2 chicks, meaning that (usually) it hatched in a nest consisting of only 2 eggs. In theory, Cainism amongst large raptors is a taxonomically, avian phenomenon as a consequence of food stress. However it was observed that food supplements do not decrease sibling aggression.

Similarly it's being said that siblicide is also common amongst Ground hornbills, although I haven't "discovered" any proof of that. Instead it appears that only 1 egg in a Ground hornbill nest hatches!?

In contrast (or similar to the above) the clutch of a Martial eagle consists of only 1 egg - which is also the case amongst most of the other eagles that do not practise Canism.

A female Wahlberg eagle also tends to mostly lay only 1 egg, although it was observed that a small percentage of these clutches had 2 eggs.

The clutch of an (African) Fish eagle usually consists of 2 eggs, although both of these eagle youngsters do not always survive. Differently to most of the other eagle species, a male Fish eagle also "shares nest duties" with the female - the couple virtually take turns incubating the eggs.

However once 1 or 2 chicks hatched, the male Fish eagle only assists feeding small nestlings. After that a Fish eagle youngster is fed mostly by the female.

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