The kori bustard (Ardeotis kori) is arguably the largest flying bird native to Africa. It is a member of the bustard family, which all belong to the order Otidiformes and are restricted in distribution to the Old World. It is one of the four species (ranging from Africa to India to Australia) in the large-bodied genus Ardeotis. In fact, the male kori bustard may be the heaviest living animal capable of flight.
This species, like most bustards, is a ground-dwelling bird and an opportunistic omnivore. Male kori bustards, which can be more than twice as heavy as the female, attempt to breed with as many females as possible and then take no part in the raising of the young. The nest is a shallow hollow in the earth, often disguised by nearby obstructive objects such as trees.
Description & appearanceThe kori bustard is cryptically coloured, being mostly grey and brown, finely patterned with black and white coloring. The upper parts and neck are a vermiculated black and greyish-buff colour. The ventral plumage is more boldly colored, with white, black and buff. The crest on its head is blackish in coloration, with less black on the female's crest. There is a white eye stripe above the eye. The chin, throat and neck are whitish with thin, fine black barring. A black collar at the base of the hind-neck extends onto the sides of the breast. The feathers around the neck are loose, giving the appearance of a thicker neck than they really have. The belly is white and the tail has broad bands of brownish-gray and white coloration. Their feathers contain light sensitive porphyrins, which gives their feathers a pinkish tinge at the base- especially noticeable when the feathers are shed suddenly.
The head is large and the legs are relatively long. The eye is pale yellow, while the bill is light greenish horn coloured, relatively long, straight and rather flattened at the base. The legs are yellowish. The feet have three forward facing toes. Females are similar in plumage but are much smaller, measuring about 20-30% less in linear measurements and often weighing 2-3 times less than the male. The female is visibly thinner legged and slimmer necked. The juvenile is similar in appearance to the female, but is browner with more spotting on the mantle, with shorter crest and neck plumes. Male juveniles are larger than females and can be the same overall size as the adult male but tends to be less bulky with a thinner neck, shorter head crest, paler eyes and a darker mantle.
During the mating season, these birds are usually solitary but for the breeding pair. Otherwise, they are somewhat gregarious, being found in groups often including 5 to 6 birds but occasionally groups can number up to 40 individuals. Larger groups may be found around an abundant food source or at watering holes. In groups, birds are often fairly far apart from each other, often around a distance of 100 m (330 ft). Foraging groups are often single-sex. Such groups do not last long and often separate after a few days. These groups are believed advantageous both in that they may ensure safety in numbers against predation and may bring the bustards to prime food sources.
Voice, singing & callLess vocal than other bustards, the kori bustard is generally silent but, when alarmed, both sexes emit a loud growling bark. This is described as a ca-caa-ca call, repeated several times for up to 10 minutes. This call carries long distances. This call is most often given by females with young and males during agnostic encounters. Chicks as young as two weeks will also emit this alarm call when startled. The male's mating call is a deep, resonant woum-woum-woum-woum or oom-oom-oom or wum, wum, wum, wum, wummm. This call ends with the bill snapping which is only audible at close range. Outside of the breeding display, kori bustards are often silent. A high alarm call, generally uttered by females, is sometimes heard. They may utter a deep vum on takeoff.
Distribution & habitatThe kori bustard is found throughout southern Africa, except in densely wooded areas. They are common in Botswana and Namibia, extending into southern Angola and marginally into southwestern Zambia. In Zimbabwe they are generally sparse but locally common, particularly on the central plateau. Their distribution range extends along the Limpopo River valley into southern Mozambique and the eastern lowveld of South Africa. In South Africa they are also infrequent to rare in the Free State, North West and Northern Cape Provinces, extending southwards into the interior of the Western and Eastern Cape Provinces. Kori bustards are absent from the coastal lowlands along the south and east of South Africa and from high mountainous areas. This species is common in Tanzania at Ngorongoro National Park, Kitulo National Park and Serengeti National Park. A geographically disjunct population also occurs in the deserts and savanna of northeastern Africa. Here, the species ranges from extreme southeast South Sudan, north Somalia, Ethiopia through all of Kenya (except coastal regions), Tanzania and Uganda. Kenya may hold the largest population of kori bustards of any country and it can even border on abundant in the North Eastern Province. They are usually residential in their range, with some random, nomadic movement following rainfall.
This species occurs in open grassy areas, often characterized by sandy soil, especially Kalahari sands, and short grass usually near the cover of isolated clumps of trees or bushes. It may be found in plains, arid plateaus, highveld grassland, arid scrub, lightly wooded savanna, open dry bushveld and semi-desert. Where this species occurs, annual rainfall is quite low, between 100 and 600 mm (3.9 and 23.6 in). Breeding habitat is savanna in areas with sparse grass cover and scattered trees and shrubs. When nesting they sometimes use hilly areas. They follow fires or herds of foraging ungulates, in order to pick their various foods out of the short grasses. They may also be found in cultivated areas, especially wheat fields with a few scattered trees. This bustard is not found in well-wooded and forested areas due to the fact that it needs a lot of open space in which to take off. In arid grassland areas it is found along dry watercourses where patches of trees offer shade during the heat of the day.
Hunting & foodWalking slowly and sedately, they forage by picking at the ground with the bills and are most active in the first and last hours of daylight. Kori bustards are quite omnivorous birds. Insects are an important food source, with common species such as locusts, grasshoppers, dung beetles (Scarabaeus ssp.) and caterpillars being most often taken. They may follow large ungulates directly to catch insects flushed out by them or to pick through their dung for edible invertebrates. During outbreaks of locusts and caterpillars, kori bustards are sometimes found feeding on them in numbers. Other insect prey can include bush-crickets (Tettigonia ssp.), termites, hymenopterans and solifuges. Scorpions and molluscs may be taken opportunistically as well.
Small vertebrates may also be taken regularly, including lizards, chameleons, small snakes, small mammals (especially rodents) and bird eggs and nestlings. They may occasionally eat carrion, especially from large animals killed in veld fires. Plant material is also an important food. Grasses and their seeds are perhaps the most prominent plant foods, but they may also eat seeds, berries, roots, bulbs, flowers, wild melons and green leaves. This bustard is very partial to Acacia gum. This liking has given rise to the Afrikaans common name Gompou or, literally translated, "gum peacock". They drink regularly when they can access water but they can be found as far as 40 km (25 mi) from water sources. Unusually, they suck up rather than scoop up water.
Breeding & matingKori bustards' breeding season is different between the two subspecies. In general, A. k. struthiunculus breeds from December to August and A. k. kori breeds from September to February. Breeding is closely tied with rainfall, and in drought years, may be greatly reduced or not even occur.
Kori bustards engage in lek mating. All bustards have polygynous breeding habits, in which one male displays to attract several females, and mates with them all. Males display at regularly used sites, each male utilizing several dispersed leks or display areas. These displays usually take place in the mornings and evenings. The courtship displays of the males are impressive and elaborate, successfully advertising their presence to potential mates. The males hold their heads backwards, with cheeks bulging, the crest is held erect, the bill open and they inflate their gular pouches, forming a white throat "balloon". During this display the oesophagus inflates to as much as four times its normal size and resembles a balloon. They also puff out their frontal neck feathers which are splayed upwards showing their white underside. The white may be visible up to 1 km (0.62 mi) away during display.
Their wings are drooped and their tails are raised upwards and forwards onto their backs like a turkey, the rectrices being held vertically and their undertail coverts fluffed out. They enhance their performance with an exaggerated bouncing gait. When displaying they stride about with their necks puffed out, their tail fanned and their wings planed and pointed downward. They also emit a low-pitched booming noise when the neck is at maximum inflation and snap their bills open and shut. Several males dispersed over a wide area gather to display but usually one is dominant and the others do not display in his presence and move away. The displaying males are visited by the females who presumably select the male with the most impressive display. Occasionally fights between males can be serious during the mating season when display areas are being contested, with the two competitors smashing into each other's bodies and stabbing each other with their bills. They may stand chest-to-chest, tails erect, bills locked and 'push' one another for up to 30 minutes.
Following the display, the copulation begins with the female lying down next to the dominant displaying male. He stands over her for 5–10 minutes, stepping from side to side and pecking her head in a slow, deliberate fashion, tail and crest feathers raised. She recoils at each peck. He then lowers himself onto his tarsi and continues pecking her until he shuffles forward and mounts with wings spread. Copulation lasts seconds after which both stand apart and ruffle their plumage. The female then sometimes barks and the male continues with his display.
As with all bustards, the female makes no real nest. The female kori bustard lays her eggs on the ground in a shallow, unlined hollow, rather than the typical scrape. This nest is usually located within 4 m (13 ft) of a tree or shrub, termite mound or an outcrop of rocks. The hollow may measure 300–450 mm (12–18 in) in diameter and be almost completely covered by the female when she's incubating. Due to their ground location, nests are often cryptic and difficult for a human to find, unless stumbled onto by chance. The same site is sometimes reused in successive years. The kori bustard is a solitary nester and there is no evidence of territoriality amongst the females. Usually two eggs are laid, though seldom 1 or 3 may be laid. Clutch size is likely correlated to food supply. They are cryptically colored with the ground color being dark buff, brown or olive and well marked and blotched with shades of brown, grey and pale purple. Eggs are somewhat glossy or waxy and have a pitted-looking surface. Egg size is 81 to 86 mm (3.2 to 3.4 in) in height and 58 to 61 mm (2.3 to 2.4 in) width. The eggs weigh individually about 149 g (5.3 oz), with a range of 121 to 178 g (4.3 to 6.3 oz)
Chicks, juveniles & raiseThe female, who alone does all the brooding behavior without male help, stays at the nest 98% of the time, rarely eating and never drinking. Occasionally she stretches her legs and raises her wings overhead. The female regularly turns the eggs with her bill. The female's plumage is drab and earth-colored, which makes her well camouflaged. She occasionally picks up pieces of vegetation and drops them on her back to render her camouflage more effective. If they need to feed briefly, the females go to and from the nest with a swift, silent crouching walk. If approached the incubating bird either slips unobtrusively from the nest or sits tight, only flying off at the last moment. The incubation period is 23 to 30 days, though is not known to exceed 25 days in wild specimens. The young are precocial and very well camouflaged. The lores are tawny, the crown tawny mottled black. A broad white supercilium bordered with black meets on the nape, extending down the centre of the nape.
The neck is white with irregular black stripes from behind the eye and from the base of the lower mandibles. The upper parts are tawny and black with 3 black lines running along the back. The underparts are whitish. When the chicks hatch, the mother brings them a steady stream of food, most of it soft so the chicks can eat it easily. Captive hatchlings weigh 78 to 116 g (2.8 to 4.1 oz) on their first day but grow quickly. The precocial chicks are able to follow their mother around several hours after hatching. After a few weeks, the young actively forage closely with their mothers. They fledge at 4 to 5 weeks old, but are not self-assured fliers until 3 to 4 months. On average, around 67% of eggs successfully hatch (testimony to the effective camouflage of nests) and around one of the two young survive to adulthood. In Namibia and Tanzania, breeding success has been found to be greatly reduced during times of drought. Most young leave their mothers in their second year of life, but do not start breeding until they are fully mature at three to four years old in both sexes in studies conducted both of wild and captive bustards. The lifespan of wild kori bustards is not known but they may live to at least 26 or possibly 28 years old in captivity.