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Biology and Natural History

The kori bustard (Ardeotis kori) is indigenous to the grasslands and lightly wooded savannas of southern and eastern Africa.

The nominate subspecies A. k. kori occurs in Botswana, Zimbabwe, Namibia, southern Angola, South Africa and Mozambique (Johnsgard, 1991), and prefers wooded grassland areas and dry savannas. In arid grassland areas it is found along dry watercourses where patches of trees offer shade during the heat of the day.

In eastern Africa, A. k. struthiunculus occurs in Ethiopia, Uganda, Sudan, Kenya and Tanzania in areas of open grasslands including karoo, bushveld, thornveld, scrubland and savanna habitats (del Hoyo, 1996). The miombo woodland of Central Africa separates the two populations.

Physical Description

  • Male and female kori bustards are alike in plumage (differences do exist in individual banding patterns)
  • Sub-adult males are equal in body size to adult males, but have a thinner neck.
  • Compared to adult males, juvenile males have shorter head crests, paler eyes and a dark mantle.
  • Juvenile males are taller than adult females.
  • Male chicks have a square head shape, brown backs and tend to be more aggressive than females when handled (Osborne and Osborne 1999).
  • Adult females are twice as small as males and have slimmer necks and thinner legs.
  • Compared to adult females, juvenile females have shorter crests and paler eyes.
  • Female chicks differ from male chicks by having a slighter, slenderer appearance to them as well as a less square shaped head (Osborne and Osborne 1999).

kori bustard


Kori bustard weight (in kilograms) comparison by subspecies and sex

Subspecies Female Male
Ardeotis kori kori 3-6 7-14
Ardeotis kori struthiunculus 6-7 13-18

The East African subspecies of kori bustard has a mottled grayish-buff coloration with dark brown vermiculations. The sides of the crown extend into a black crest. There is a white stripe over each eye. The chin, throat, and neck are creamy white mixed with black bands.

The underparts are buff colored with dark brown vermiculations. The tail has wide bands of grayish brown and white. The primaries are also similarly marked. The shoulder area has a checkered black and white pattern (Osborne and Osborne 1999).

The southern race is similar in appearance, but is slightly taller (pers. obs.) with minor plumage differences especially in the facial area.

In the field, the kori bustard can only be mistaken for the slightly smaller Arabian bustard (Ardeotis arabs), although the two species only come into contact in a very small area of northeastern Africa.

The species is generally silent. When alarmed however, both sexes emit a loud bark. Chicks as young as two weeks will also emit this alarm call when startled (personal observation).

The shock display may also be performed when a bird is alarmed. In this defensive display, the bird bows forward, lifts its tail feathers, and spreads and inverts its wings, thus seeming to appear larger to any potential predator.

Kori bustards are one of the largest species in the bustard family, and males approach the weight limit for flying. They generally prefer to run away from any danger, although they will fly, but usually only reluctantly. As with all bustards, they lack a hind toe. They are strictly terrestrial, although there is a report of a bird sighted in Kenya perched at the top of a tree (L. Hudson, pers. comm).

Kori bustards have no preen gland. To keep clean, they produce a powder down. Sun bathing and dust bathing are practiced. Their feathers contain light sensitive porphyrins, which gives their feathers a pinkish tinge at the base- especially noticeable when the feathers are shed suddenly.

Diet

Kori bustards are omnivorous birds with insects forming a large part of their diet. They also consume a variety of small vertebrates such as mammals, lizards, snakes and birds. Seeds and berries of a variety of plant materials are also eaten as well as the gum from Acacia trees which has earned them the name Gompou’ (Afrikaans for “gum-eating bird).

They are one of the few species of birds known to drink water using a sucking action rather than scooping it up with their bill (Hallager, 1994). They feed mostly in the early morning and late afternoon and rest during the heat of the day.

Movements

The species is not migratory in the true sense, but preliminary evidence by Osborne and Osborne (1998) indicates that juvenile and adult males undertake extensive movements (up to 120 km) after the breeding season. Juvenile females do not appear to undertake such movements.

In general though, very little is known about the movements or migration patterns of either population (although trial satellite tagging of one male kori bustard by the National Museums of Kenya demonstrated a migration along the Rift Valley between Tanzania and southern Sudan, (Njoroge et. al. 1998)).

Reproduction

Kori bustards exhibit little sexual dichromatism but substantial sexual dimorphism with males weighing twice as much as females. Males approach the weight limit for flying and weights of 16-19 kg are commonly seen in mature adult birds (A.k.struthiunculus).

Kori bustards are a polygynous species with a tendency towards gregariousness outside the breeding season. Breeding is closely tied with rainfall, and in drought years, may be greatly reduced or not even occur (Osborne and Osborne 2001).

Male bustard with balloon display During the breeding season, males gather either singly or in loose lek like formations and perform “balloon” displays to attract females. Displays can occur throughout the day, but are usually most intense in the early morning and late afternoon/evening.

During the height of the male display, the esophagus inflates to as much as four times its normal size and resembles a balloon. This display may be seen up to 1 km away. With the neck expanded, the tail and wing feathers pointed downward, and the crest erected, the male emits a low-pitched booming noise as he snaps his bill open and shut.

Male bustard displaying Females presumably are attracted to the male with the most superior display. Prior to copulation, the male spends about five to ten minutes pecking on the head of the recumbent females (personal observation).

Actual copulation lasts no more than a few seconds. Once over, the male leaves and resumes displaying to attract another female. He plays no role in incubation or chick rearing.

As with all bustards, the female makes no real nest other than a shallow scrape and the eggs are laid on the ground. The nest is usually near a small clump of grass so the female is partially hidden. The clutch is one or two eggs and very rarely (Osborne and Osborne 2001) three eggs. The incubation period in captivity is 23 days.

The precocial chicks are able to follow their mother around several hours after hatching and remain with her until the start of the next years breeding season- well after the fledging period of four weeks. Sexual maturity for females has been documented in the wild at three years (T. Osborne pers. comm) and in captivity at three years. Sexual maturity of wild males has not been documented although in captive birds, first reproduction has occurred at three years.

Life spans in the wild are not known, but the longevity record in captivity is 26 years. In the wild, the subspecies A.k.struthiunculus breeds from December to August; A.k.kori breeds from September to February.

Rainfall plays a strong role in breeding success in both subspecies with breeding greatly reduced during times of drought in Namibia (Osborne and Osborne 2000) and in Tanzania (Osborne, P. 1984)

Relationship to Animals and Humans

Natural predators of kori bustards include martial eagles, tawny eagles, Verreaux's eagles, leopards, lions, caracals, and jackals.

The most vulnerable time for the birds is when they are chicks with mortality rates approaching 82 percent in the first year of life (Osborne and Osborne 1998).

A well-documented foraging association exists between kori bustards and Carmine bee-eaters (Merops nubicus and Merops nubicodes). These birds often perch on the backs of kori bustards. Only active, foraging kori bustards seem to be chosen by the bee-eaters as perching sites. The bee-eaters eat insects stirred up by the kori’s as they move about. In return, the kori bustards may receive some form of predator detection (Jackson 1945, Viljoen 1987).

Kori bustards figure in dances and songs of the Bushmen of Botswana and drawings of kori’s have been found in caves.

Status of Kori Bustards in the Wild

In the wild, there are two populations of kori bustard with Ardeotis kori struthiunculus residing in eastern Africa and the nominate race, Ardeotis kori kori occurring in southern Africa.

The species is listed on Appendix II of CITES, and the 2000 Eskom Red Data Book for Birds lists the status of A. k. kori as Vulnerable, estimating that in the next three generations, it is expected to decline by 10% in South Africa (Barnes, 2000).

Throughout its range, the species is uncommon to locally common, but generally declining (Urban, 1986). The habitat of both subspecies is under threat from crop farming, over grazing by livestock and bush encroachment.

According to del Hoyo (1996), the kori bustard is showing signs of chronic decline and local extinction over its entire range. In eastern Africa, protected areas (e.g. National Parks) offer good protection for the species and viable breeding populations can be found in Tanzania, Kenya and Uganda.

Viable populations exist in unprotected areas as well (e.g. Ethiopia and Sudan, and in Tanzania around Lake Natron and in the foothills of Mt. Kilimnajaro,) but in these areas, the birds are hunted. Threats to kori bustards in eastern Africa include increasing agricultural development (Ottichilo, 2001), hunting pressure, a low tolerance for human activity and an inherent low reproductive rate (Dale, 1990).

Severe drought in the Serengeti (1993) and the Masai Mara (1984, 1986 and 1993) almost certainly reduced the level of breeding activity (Ottichilo, 2000). Total population size has not been reported for eastern Africa.

In southern Africa, signs of chronic decline are reported in the Transvaal, Orange Free State and parts of Cape Province, South Africa (Allan, 1989), and Parker (1994) noted that A .k. kori became extinct in Swaziland prior to 1960. While Botswana, Namibia and Zimbabwe are the stronghold for the species in southern Africa, kori bustards are under severe pressure particularly in Botswana (Harrison, 1997).

Causes for the decline of the species in southern Africa include increasing agricultural development, hunting pressure, collisions with overhead power lines, a low tolerance for human activity and an inherent low reproductive rate (Dale, 1990). Reduced breeding activity in dry years compounds the problem. Suitable savanna habitat is being lost through bush encroachment caused by over-grazing from livestock. Total population size has not been reported for southern Africa.

Although the distribution of both races is well documented, total population size is unknown for either subspecies. In addition, very little is known about the movements or migration patterns of either population (although trial satellite tagging of one male kori bustard by the National Museums of Kenya demonstrated a migration along the Rift Valley between Tanzania and southern Sudan, (Njoroge et al, 1998)). Consequently, the conservation status of the kori bustard is based on insufficient data.

Present Range vs Historic Range of Subspecies

Present range of Ardeotis kori struthiunculus The present range of this subspecies is smaller than in previous times. In Ethiopia the species is now found only south of 9º latitude. From there, the range extends west to the extreme southeastern part of Sudan and south to western Kenya and northeastern Uganda.

There are no records of birds in Somalia since 1970. In Tanzania, it is restricted to the northern plains (P. Goriup, pers. comm., and N. Baker, pers. comm.). It is scarce around the coastal lowlands of Tanzania and Kenya (Zimmerman, 1996).

Historical distribution of Ardeotis kori struthiunculus

The subspecies historically ranged throughout most of Ethiopia (Ash, 1989) and southeastern Sudan (below 9º latitude).

From there it ranged southeast to northwestern Somalia and then west and south to northern Uganda, Kenya and the highlands north of the Singida providence in Tanzania.

Present range of Ardeotis kori kori

The present range of this subspecies is smaller than in previous times. It is now distributed in the semi-arid areas in the western half of southern Africa to include Namibia, extreme southern Angola (rare visitor), western Zambia, Botswana, western Zimbabwe, South Africa and the Limpopo Valley of Mozambique.

In South Africa, it is found mainly in the Transvaal lowveld and the northern Cape Province, as well as the Kruger and Kalahari Gemsbok National parks (Kemp, 1980) although it is very scarce along the eastern border of Kruger National Park (Barnes, 2000) near Mozambique.

It is a vagrant in Lesotho (Goriup, pers. comm). Allan (1988) reported that the species has declined in the Transvaal, Orange Free State and parts of Cape Province and Parker (1994) noted that this subspecies went extinct in Swaziland prior to 1960.

Historical distribution of Ardeotis kori kori

This southern race historically ranged throughout most of southern Africa including Zimbabwe, Botswana, southern Angola, Namibia, South Africa, southern Mozambique (Johnsgard, 1991) and Swaziland (Harrison, 1997).

Status of Habitat, Total Population Size and Size of Population Fragments

Throughout its range, the species is uncommon to locally common, but generally declining (Urban, 1986).

The habitat of both subspecies is under threat from the spread of agriculture, high human densities, illegal hunting, over grazing by livestock and bush encroachment.

According to del Hoyo (1996), the kori bustard is showing signs of chronic decline and local extinction over its entire range. Total population size has not been reported for either subspecies.

Status of habitat, total population size and size of population fragments of Ardeotis kori struthiunculus

The entire East African region is currently undergoing widespread ecological changes as a result of increased agricultural practices and other forms of land use (Mwangi, 1989). The area of land used for agriculture has increased since 1950 by 26% (Happold, 1995).

Lado (1996) states that the most serious threat to the future of wildlife in Kenya is habitat destruction and/or altercation. In the Masai Mara for example, the area used for wheat production has grown from 4875 ha in 1975 to over 50,000 ha in 1995.

In the nearby Loita plains, (where kori bustards are known to frequent), wheat production continues to expand as the human population grows and farmers realize the agricultural potential of the land. As areas used for agriculture expand in Kenya, it can be expected that the numbers of wildlife, including kori bustards will decline (Ottichilo, 2001).

In addition to the spread of agriculture, urbanization, pollution, the use of pesticides, including those that are banned in other countries, and other consequences of an exploding human population all contribute to a deteriorating situation for many species of wildlife, including kori bustards.

Population size/status per country:

Sudan -- Breeding populations exist in the extreme southeastern area of the country, but total population size is unknown. Possibly only a dry season visitor to this country (Nikolaus, 1987).

Kenya -- In Kenya, kori bustards are most numerous in the dry grassland areas of northern and western Kenya and the Rift Valley highlands south to Mara Game Reserve, Loita Plains, Nairobi National Park and Amboseli National Park. They are scarce and localized from the Tana River south to Tsavo West and Tsavo East National Park (Zimmerman, 1996). Total population size is unknown. Mwangi (1988) estimated 0.3 birds per km2 in Nairobi National Park in 1986/87.

Uganda -- In Uganda, breeding populations exist in Acholi, Lango and Kidepo National Park. Total population size is unknown.

Ethiopia -- Kori bustards were formally fairly common in Ethiopia south of 9º latitude, but numbers have declined (Goriup, per. comm). Total population size is unknown. Somalia -- There are no records of birds in Somalia since 1970.

Tanzania -- In Tanzania, the Serengeti National Park, Ngorongoro Conservation Area, Tarangire National Park, Maswa Game Reserve, Arusha National Park and Mkomazi Game Reserve offer long term protection and viable numbers of birds can be found in these protected areas. It is still relatively common in the Rift Valley highlands. There is a small and isolated population in central Tanzania, which occupies a small area at low densities (N. Baker, pers. comm.) It is regarded as scarce around the coast (Zimmerman, 1996). The birds are hunted around the Lake Eyasi Basin, Lake Natron and in the foothills of Mt. Kilimnajaro (N. Baker, pers. comm.). Total population size is unknown. Total population size has not been reported in East Africa nor has it been reported for individual countries.

Status of habitat, total population size and size of population fragments of Ardeotis kori kori

In general, the greatest numbers of kori bustards in southern Africa are to be found in protected areas where for example in Botswana, birds were 45 times more frequently seen in protected areas than on unprotected areas (Herremans, 1998). The species is listed in the South African Red Data book as a vulnerable species (Brooke, 1984) and more recently, in the Eskom Red Data book of Birds of South Africa, Lesotho and Swaziland (2000) also as vulnerable.

Population size/status per country:

Botswana -- Despite low human densities in Botswana, kori bustards are under severe pressure from habitat loss. Nonetheless, strongholds for the species in Botswana include the Kalahari Gemsbok National Park (est. 100-140 birds (Barnes, 2000)), Central Kalahari Game Reserve, Nxai Pan National Park and the Chobe National Park where road counts found 1 bird/106km. However, in unprotected areas, the density level dropped to 1 bird/4356 km (Harrison, 1997). Suitable habitat for kori bustards has been lost in Botswana due to grazing by livestock, which have increased dramatically over the past 100 years. Livestock numbers continue to grow despite reports of overgrazing and forecasts of devastating long-term land degradation since the early 1970’s. Grazing pressure has resulted in habitat deterioration of large grassland species such as the kori bustard (Herremans, 1998). Total population size is unknown.

Namibia -- The stronghold for kori bustards in Namibia and possibly the world is in Etosha National Park where Osborne (1998) found 1 bird/16km. Outside the park boundaries however, birds are hunted.

Zimbabwe -- Suitable habitat for kori bustards is deteriorating through overgrazing by livestock and the situation is similar to that in Botswana. The species has decreased in several areas most noticeably in the Mashonaland plateau (Harrison, 1997) where birds are hunted.

The decline in this area was first noticed in the 1920's (Irwin, 1981). Total population size in Zimbabwe has been variously reported in 1980, when an estimation of 10,700 birds was given by Rockingham-Gill (1983), although Dale (1990) reported 5000 birds and Mundy (1989) estimated 2000 birds and states that Rockingham-Gill's 1983 estimate is vastly over estimated.

Total population size is unknown. Matabeleland is the stronghold for the species in Zimbabwe (Rockingham-Gill, 1983).

South Africa -- In South Africa, numbers have declined in the 20th century, but the extent of the decline is unknown (Brooke, 1984). Kruger National Park supports 100-250 individuals (Barnes, 2000). Outside protected areas, kori bustards are found in relatively large numbers only in the Platberg-Karoo Conservancy in South Africa (Barnes, 2000). Allan (1988) reported that the species has declined in the Transvaal, Orange Free State (where it is uncommon to rare) and parts of Cape Province. Total population size is estimated to be between 2000-5000 birds.

Mozambique -- It is locally threatened in Mozambique and probably numbers less than 100 birds (Parker, 1999). Hunting is the biggest threat.

Other -- Parker (1994) noted that this subspecies went extinct in Swaziland prior to 1960. In Angola, the species is a rare visitor. In Zambia, kori bustards are found only west of the Zambezi River although their status there is unclear. The Sioma Ngwezi National Park may offer protection. It is considered very sparse in Natal with one sighting reported in 1976 (Cyrus, 1980).

Natural and Human Induced Environmental Factors Affecting the Species

Most bustard species are in decline everywhere they occur. The main threat to kori bustards in the form of human induced factors includes habitat destruction through increasing agricultural development (Dale, 1990; Ottichilo, 2001) and bush encroachment caused by over-grazing from livestock.

Poison used to control locusts is toxic to birds and may possibly be affecting kori bustard populations (Barnes, 2000).

Although the kori bustard is listed as “protected game” it is still hunted over much of its range. In Namibia, it is commonly referred to as the “Christmas turkey” (Osborne, 2001) and in South Africa it is called the “Kalahari Kentucky”(Barnes, 2000). It continues to be hunted throughout its entire range.

Collisions with overhead power lines are a continual problem as exemplified by one 10-km stretch of overhead powerlines in the Karoo that killed 22 kori bustards during a five-month period (Rooyen, C, undated).

Natural factors effecting the species include an inherent low reproductive rate, and reduced breeding activity in dry years with predation pressure a constant.

In addition, favored areas such as tree-lined watercourses are becoming unsuitable for kori bustards because they are being invaded by alien plant material (Barnes, 2000).

Compiled by Sara Hallager, SSP Coordinator for the Kori Bustard