Crowned Eagle's Nest Traditional Cache
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Crowned Eagle
Crowned Eagle Giba Gorge is a bird watchers paradise with over 200 species having been recorded in this general area. A checklist of the species likely to be found in Giba can be downloaded from here.
GGEP_bird_checklist
If you are serious about bird watching and would like to contribute to bird conservation in South Africa, visit the South African Bird Atlasing project website http://sabap2.adu.org.za and submit your Giba lists here (in the prescribed format).
The sand road and planned trails all offer good access to the forest, woodland, wetland and grassland habitats in the area. Some of the specials include:
African Crowned Eagle
There are two nests of this species in the GGEP, one in the main gorge near the river (and visible from the sand road) and the other in MacIntosh Falls area, adjacent the freeway. This large and powerful raptor is well known for its hunting skills in forest environments where it feeds on monkeys, dassies, large birds, such as Hadedas, and many other forest animals.
Photo credit: Hugh Chittenden
Although the Crowned Eagle's long tail imparts an overall length up to 90 cm (35 in), it is somewhat less massive and has a considerably shorter wingspan than Africa's largest eagle, the Martial Eagle (Polemaetus bellicosus). It is nevertheless considered Africa's most powerful eagle when measured in terms of the weight of its prey items.It often preys on mammals such as Bushbuck (Tragelaphus scriptus), exceptionally weighing up to 30 kg (66 lb) albeit usually much less. The Crowned Eagle possesses unusually large talons and strong hindlegs, and may kill by crushing the skull. The Eagle is also ferocious; some records from beneath a nest show the remains of a large, male Sooty mangabey weighing 11 kg (24 lb).
Due to their ecological similarities, the Crowned Eagle is Africa's best analogue of the Harpy Eagle (Harpia harpyja). Thanks to its bold and highly conspicuous behavior, it is exceptionally well-studied for a large, forest-dwelling eagle. Due to a relatively high level of habitat adaptability, it was until recently considered to be faring well by the standards of large, forest-dependent raptors. However, today it is generally thought that it is decreasing far more than was previously perceived due to the almost epidemic destruction of native tropical African forest. It is now listed as Near Threatened.
Breeding
Crowned Eagles have one of the most prolonged breeding cycles of any bird. It is common for raptors that live around the tropics to have a relatively elongated breeding period. Crowned Eagle pairs breed once every two years; a single breeding cycle lasts for approximately 500 days in duration. Most other eagle species complete a breeding cycle in under six months, or in about 35% of the time it takes the Crowned Eagle. While the incubation and nestling stages are about average for a tropical eagle (for example the Black-breasted Snake-Eagle (Circaetus pectoralis), about half the weight of this species, has an incubation/nestling cycle of a similar length), it is the extraordinary post-fledging period of 9–11 months that makes the Crowned Eagles’ breeding cycle so long. In Harpy and Philippine Eagle, although these are less extensively studied, it may take a similar or even longer amount of time for the young to attain full independence. A case of Crowned Eagle pairs that reportedly bred every year in South Africa are unsubstantiated but may be due to an apparently high population loss rate among juvenile eagles near areas that are heavily populated by humans. Breeding can occur almost year-around throughout the range, though egg laying seems to peak roughly around the end of the African wet season or the early dry season, from July to November. Territories or home ranges are maintained vigorously. In Zimbabwe, individual home ranges can vary from 140 to 200 km2 (54 to 77 sq mi) in size. Near the city of Nelspruit in South Africa, home ranges averaged 30 km2 (12 sq mi) in size. In southern Africa, the mean distance between active nest sites can range from 2 to 19.5 km (1.2 to 12.1 mi).
After engaging in the breeding display described above, the pair collaborate in building a massive nest in a fork of a large forest tree, typically from 12 to 45 m (39 to 148 ft) above the ground. While the female fetches more nesting material, the male tends to be more active in nest construction. In East Africa, many nests appear to be close to a forest river. Generally, Crowned Eagles seem to be attracted to the taller trees in the forest. On the Nyika Plateau in Malawi, the favorite nesting trees are the large emergent Aningeria adolfi-friedericii and Chrysophyllum gorungosanum, and a pair in the Lower Shire used a Sterculia appendiculata tree. In Zimbabwe, Newtonia buchananii are reportedly one of the most used tree species for nesting. Exceptional Crowned Eagle nests have been observed on sheer cliff faces. In southern Africa, the species nest in drier and denuded terrain than expected such as Adansonia stands on semi-arid hillsides. Despite the relative sparseness of this habitat, these sites have a varied and convoluted terrain, with nooks and crannies, valleys, overhangs and hideaways that allow a Crowned Eagle to exercise its particular hunting skills. In Kenya, similar fractured landscapes can also be utilized by Crowned Eagles, such as the black gigantic volcanic rubble fields of Tsavo West National Park, the lower Chyulu Hills, Kibwezi and Soysambu Conservancy. These are jungles of boulders covered with low growth interspersed (in the past) with high trees. A nest built from scratch may take up to 5 months to construct, however existing nests are often repaired and re-used during successive breeding seasons, a process that can take as much as 3 months. It is typical for an eagle pair to use a nest for more than five years and, unlike several other booted eagles, Crowned Eagle pairs rarely build more than one nest for alternate use. Most large eagles build a very large nest and the Crowned Eagle is no exception, as it builds one of the largest nests of any eagle. In the first year they build a nest, it may measure 1.5 m (4.9 ft) across and 50 cm (20 in) deep. However, a larger nest, usually after several years of usage, may measure up to 2.5 m (8.2 ft) across and up to 3 m (9.8 ft) deep. The nest may consists of both dead and greener branches and have a light coverage of leaves and animal matter. Copulation takes place in the nest, several times a day. Reportedly copulation can occur up to a year before laying, although these may be exceptional cases of mating for non-fertilization purposes (which, in other eagles, has been thought to be related mainly to strengthening pair bonds). A pre-copulation display typically occurs, wherein the male runs repeatedly around the crouching female with wings upraised, which displays the chestnut of the under-wing coverts and beautiful barring.
In South Africa the Crowned Eagle lays its eggs from September to October; in Zimbabwe, it lays from May to October; mainly near October around the Congo River; anywhere from June to November in Kenya, with a peak in August through October; in Uganda from December to July; and in West Africa, laying peaks in October. The clutch of the Crowned Eagle either contains 1 or 2 eggs. Often in East Africa, just one egg is laid. Eggs are usually just white, though may sometimes be overlaid with sparse red-brown markings. The eggs are moderate in size, averaging 68.2 × 53.6 mm (2.69 × 2.11 in), with ranges of 60.9–75.5 mm (2.40–2.97 in) in length and 50.8–57.9 mm (2.00–2.28 in) in width. When a natural disaster befalls a nest, a replacement may be made in 2 months time. Incubation lasts for approximately 49 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. Male brings food to the incubating female every 3 to 5 days. When they initially hatch, the young tend to be quite quiet. If two eggs are laid, the younger one dies by starvation after being outcompeted for food by the older one or even directly killed by its older sibling. No nest of wild Crowned Eagles has been known to successfully produce more than one fledgling, though in captivity two have been known to survive with human interference (supplementally feeding the younger chick or taking it out of the nest). In cases where the older nestling dies, the younger one may be fed more regularly and survive.
After hatching, the male kill rate rises to one kill every 1.5 days. Pair behavior while raising chicks is very variable, some males are very attentive to their young, while others leave virtually all brooding to the female. After 40 days of age, the young is capable of feeding itself, though is often still fed. The first feathers through the white down emerge when the Crowned Eagle chick is 40 days old, with the feathers ultimately covering the down in 76 days. After 76 days, the main feather development is in the tail or the wings. Wing-flapping begins at 45 to 50 days, increasing after around 75 days. The young fledge at 90 to 115 days, with an average 110.6 days and any period of time less than 100 days is considered unusually soon. On average, male chicks tend to be more active wing-flappers and usually will first fly around 10 days earlier than the more phlegmatic female chicks. After fledging, females are attentive 95% of the day and brood 50-75% of the day, the amount decreasing slightly with each day. The female does much of the prey capture and a majority of the nest defense after the young fledge. After fledging, the young remain in the neighborhood of the parent’s nest and are feed every 3 to 5 days by either parent for their first 270–350 days of life. The rate of food-delivery varies from several times a day to every 3 days on average during the post-fledging period. The fledged juvenile will solicit adults (apparently even unrelated adults) for prey but does not actually take the prey unless this occurs around the nest site. The first recorded kill for a young Crowned occurred 61 days after fledging, although this is considered exceptionally early by the standards of this species. Flights increase incrementally through the post-fledging period, although the young do not engage in rising flights until they are fully independent. Independence seems triggered by the increased indifference of parents to bringing food. Due to the loud vocal interplay between the parents and the fledging eagle, the adults seem to take it as a sign that their offspring has sought independence if they return to the nesting area and hear no right auditory response. The young eagle usually remains in the care of its parents for a total of up to 11 months after it fledges, longer than is known in 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. In 34 possible cases, 18 resulted in eggs being laid. Fledging success is approximately 83% and almost all young that leave the nest also reach independence. Early estimates that it takes up to 20 years for this species to reach adulthood are, of course, erroneous and it is estimated that most Crowned Eagles will reach breeding maturity at around five years old, as is typical for large eagles.
Information courtesy of Wikipedia
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