African Wildlife & Environment Issue 78

BIRDING

Eagles start hunting soon after dawn, and mainly kill early in the morning and in the evening prior to sundown. Being a forest-dwelling species, the Crowned Eagle has no need to travel great distances to hunt, nor employ a great deal of active hunting flight (such as soaring seen in savannah-dwelling species). Rather, it tends to hunt passively. Crowned Eagles may locate a suitable hunting spot by listening (such as via the call of the noisy vervet monkey) or watching for prey activity, though they may also use habitual hunting perches where they've previously had hunting successes. These eagles often still-hunt, wherein they drop or stoop onto prey from a branch perch. Following the sighting of suitable prey, the eagle quickly and stealthily maneuvers itself through the forest towards its prey, a certain element of surprise inherent in its final approach. Most of the Crowned Eagles’ kills are made on the forest floor. Arboreal prey may be forced to the ground during an attack. The sharp, powerful talons may produce sufficient force to kill the prey on impact; if not, death from trauma or asphyxiation soon follows. Several prey items have been killed by ramming the talons into the skull and penetrating the brain. Having killed on the ground, it can fly almost vertically upwards to a branch, while carrying its prey before feeding. Pairs may collaborate in capturing prey, with one bird flushing the prey so the other can glide in unseen and ambush it. The staple diet of this raptor is mostly mammalian. One estimate of the typical prey range posited that the weight range is from 1 to 5 kg but known to routinely attack prey weighing more than 9 kg. According to some authorities, typical prey sizes may be considered to range to at least 20 kg in body mass. Reportedly, the Crowned Eagle can lift more than its own body weight in flight, though verified accounts of this are sparse. The Crowned Eagle occupies a unique niche, as it is the only bird in which primates are the most taken prey at the species level. Outside of the rainforest, the Crowned Eagle's diet tends to be somewhat more diverse. While they may take monkeys on a relatively small scale, other families, largely the antelopes and the hyraxes, are the leading prey. Other mammals have been recorded as opportunistic prey.

breeding seasons, a process that can take as much as three months. In the first year they build a nest, it may measure 1.5 m across and 50 cm deep. However, a larger nest, usually after several years of usage, may measure up to 2.5 m across and up to 3 m deep. The nest consists of both dead and greener branches and has a light coverage of leaves and animal matter. Most pairs then use this nest for many years.There is one record of a nest being used for over 50 years. It seems that a new nest is built only if the old one falls down. In South Africa, the Crowned Eagle lays its eggs from September to October; in Zimbabwe, it lays from May to October; mainly nearer to October. One or two eggs are laid, usually just white, though may sometimes be overlaid with sparse red-brown markings. The eggs are moderate in size, averaging 68.2 mm × 53.6 mm. Incubation lasts for approximately 49 - 51 days. 80 – 90% of egg incubation is done by the female during the day. Food is mainly brought to the nest by the male in the early stages of breeding, though sometimes both sexes may deliver food. The male brings food to the incubating female every three to five days. If two eggs are laid, the younger one dies by starvation after being out-competed for food by the older one, or even directly killed by its older sibling. The young eagle usually remains in the care of its parents for a total of up to 11 months, after it fledges.This is the longest period when compared to almost any other raptor. The advantage of this prolonged stretch to independence is that it may make for a stronger young eagle when compared to other accipitrids, which have almost no post- fledging dependency period. It is estimated that most Crowned Eagles will reach breeding maturity at around five years old, as is typical for other large eagle species. The average life expectancy for Crowned Eagles is 14 years Hunting behavior and prey The Crowned Eagle is often described as the most powerful raptor in Africa. In the deep forest, an adult eagle may cover a hunting range of up to 6.5 to 16 km 2 , with the home ranges being smaller for those that inhabit rocky hills and cliffs abounding in hyraxes.

45 | African Wildlife & Environment | Issue 78 (2021)