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Birding with Nico Myburgh

From Issue No 17

Talons of death

 

Crowned Eagle – Stephanoaetus coronatus (Afrikaans: Kroonarend)

 

The Crowned Eagle is the largest and fiercest of all the African eagles, although the wingspan of the Verreauxs’ Eagle (formerly Black Eagle), Martial Eagle and Tawny Eagle is longer. It is normally considered to be a purely forest eagle, common to Tropical Africa, but it sometimes occurs in more open country as well. In South Africa it is found in the eastern parts as far south as Knysna and as far west as Grootvadersbosch near Heidelberg.

The talons are the main killing instruments, not the beak. The prey of Crowned Eagles varies according to the habitat. In thick forest areas they take mainly Vervet Monkeys, in more open forest they take Blue Duiker, Forest Duiker and even occasionally Bushbuck which could weigh up to 17 kg. The killing is almost always instantaneous. They grab hold of the head of the antelope or monkey with their talons, then the three centimetre long claw on the back toe is forced into the brain of the animal, killing it instantly.

The skulls of about fifty animals, monkeys, antelope, dassies, etc were collected at a number of nests by a researcher. All had the telltale hole in the back of the skull. The Crowned Eagle just cannot afford to have a long fight with any animal heavier than itself (a male Crowned Eagle only weighs about 4,5 kg).

The nest is a very big structure of sticks in a large tree. It is used for many years and is added to every breeding season. They sometimes have a second nest used alternately, when the prey in the area near the first nest gets scarce. The nests may be up to 15 or 20 km apart.

The eagle normally lays two eggs, sometimes only one, but the first chick to hatch will always kill the second one (the Cain and Abel Syndrome!). The nestling period is very long, almost 114 days. After that the chick remains with the parents until the next breeding season, which may be for a period of up to two years. It then goes off on its own without aggression from the parents, as is the case with some other eagles.

The female Crowned Eagle is considerably bigger than the male. Even in one-year-old birds the female chick is larger than the male.

The hunting technique is very interesting. The birds work together. The female flies low over the trees when Vervet Monkeys are gathered. The monkeys then all scamper up to the tops of the trees. The male in the meantime has approached from below the canopy. The bird shoots up from below and grabs a monkey, then kills it in flight. He then brings it to the perch, usually a rock or dead tree, to pluck the hair off the stomach area to start eating. We got hold of a large monkey which had been killed (a risky business) and weighed it – 7 kg, much heavier than the bird itself. Antelope and other small animals are killed on the forest floor.

In 1993 Hugh Chittendon and I found a breeding nest in Dlinza Forest near Eshowe in Zululand. I then spent over 200 hours in a hide 22 metres above the ground to observe the parents and their chick, especially to record feeding patterns. Apart from the diet of meat, the parents on seven occasions also brought metre-long branches of the Strychnos mitis tree to the nest, where the chick would eat all the green berries off the branch. These fruits, about the size of coffee beans, are also much sought after by monkeys and hornbills, and related trees are utilized in traditional African medicine. No other fruit was brought to the nest, and it was the first time that eagles were observed feeding their young with berries.

The Crowned Eagle is unfortunately only a mere visitor to the Western Cape and then it is probably a sub-adult, going on what John Martin, a well-known birdwatcher from Somerset West, called, "the grand tour", which all sub-adult eagles do before they settle in their own territory.

It might be of interest to note that one nest of a Crowned Eagle in Grahamstown was in use for 75 years. The explanation is that when one of the pair dies the other takes a new mate and so it goes on. Other nests have been in use nearly as long. In Kwazulu-Natal the Crowned Eagle is very popular with the sugar farmers. A farm that is lucky to have a resident pair has no problems with Vervet Monkeys. They can do a great deal of damage to sugar cane, but with a pair of Crowned Eagles around they stay inside the forested areas.

In Dlinza Forest a feral cat was catching birds at a drinking pool. The Nature Conservation trained game guards did everything to catch it, even consulted their sangoma. No gain. A few days later I was sitting in the hide with a five-week-old chick in the nest and in flew the male eagle with the cat in its talons. It took the chick two days to eat it.

 

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A Crowned Eagle swoops with its deadly talons extended

The eagle swoops with its deadly talons extended

A male Crowned Eagle with its prey on a perch

A male with its prey on a perch

The "crown", here seen raised, that gave the Crowned Eagle its name

The "crown", here seen raised, that gave the Crowned Eagle its name. This portrait also shows the wide-set eyes, which give raptors binocular vision to accurately judge the distance from their prey

A female Crowned Eagle with her prey, a vervet monkey

A female with her prey, a vervet monkey

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