The Kori Bustard is either the heaviest or second heaviest bird that can fly. The other contender is the Great Bustard.
The Kori Bustard lives in the northeastern fourth of Africa. It has a varied diet, but prefers seeds and lizards.
It spends most of its time on the ground and only flies when it absolutely must.
Classification:
Order: Gruiformes
Family: Otididae
Genus: Ardeotis
Species: A. kori
Photos:
Kori Bustard all puffed up in courtship display

"For want of a better word, they "boomed" trying to attract the opposite sex."
The Worlds Heaviest Flying Bird - The Kori Bustard (Gompou in Afrikaans) seen in Pilanesburg National Park South Africa

"Taken by my partner Allan Class: Aves, Order: Gruiformes Family: Otidedae Species: Ardeotis Genus: kori My partner pointed this bird out to me and said it was a Bustard - I told him to mind his language!!!! But no really it IS a "Bustard" - Dictionary definition - modification of Middle French "bistarde", from Old Italian "bistarda", from Latin avis tarda, meaning literally, "slow bird" (although it is not slow)! Allan knew it was a Bustard because In the UK another member of the same family the "Great Bustard" became extinct in the British Isles between 1832 and an artificial reintroduction to Salisbury Plain in 2004. It forms part of the design of the Wiltshire Coat of Arms - A County in Southern England in the area where we come from. see greatbustard.com The South African Kori Bustards are HUGE looking like a cross between an ostrich and a monitor lizard. Except for feathers, the kori bustard seemed reptilian, with piercing yellow eyes, thick long legs ending in tiny feet, a stiletto-like bill, and a long grey & black-peppered neck. Kori Bustards are large, heavy, mainly terrestrial birds. It is the heaviest bird capable of flight, although this title may also belong to the similarly-dimensioned Great Bustard. However it avoids flying if possible. It spends most of its time on the ground, foraging for the seeds and lizards which make up most of its diet. The male Kori Bustard averages at about 110 cm (3.7 feet) in length and stands 60-90 cm (2-3 ft) tall. An average male bird would weigh about 13.5 kg (30 lb), but exceptional birds may weigh over 20 kg (44 lb). A report exists of a 34 kg (75 lb) bird, but it is not verified and must be beheld with skepticism because it so much heavier than any other recorded weight for a Kori Bustard. The female Kori Bustard averages 7.7 kg (17 lb) and is usually 20% shorter than a male. The Wingspan is 2.4 meter (7.9 ft) - So bearing that in mind - if you one coming towards flying at low level you I would duck!!!!! Image being hit by something about twice the size of two large Christmas Turkeys. Once they do get off the ground, the bustards, despite their large size, are able to fly at a high velocity (60 kilometre/hour) The southern subspecies (Ardeotis kori kori) is distributed in southern Africa in Botswana, Zimbabwe, Namibia, southern Angola, South Africa, and southern Mozambique. Kori Bustards are birds of wide, open grasslands, and lightly wooded savanna. The subspecies kori can be found in arid savanna areas where trees are scattered intermittently, they are fond of areas where the grass is short and where there is a good view of the surrounding area. Migrations in response to rainfall and/or food supply have been recorded, but the species is not migratory in the true sense. The distribution of the kori subspecies is becoming fragmented and overall, declining in numbers. Local extinctions have been recorded. Given the continual habitat destruction from agriculture and development, hunting pressure, and a slow reproduction rate, Kori Bustards do not face a promising future in the wild. Many Kori Bustards are poached for local consumption, mainly by men over 30, Snares or Guns are used to kill birds. In some areas only tribal elders are allowed to eat bustard meat. Sometimes a traditional doctor is brought in to ‘treat’ it before it is eaten, because of a belief that bustard meat can otherwise cause mental illness. There is evidence of illegal cross-border trafficking in live bustards from Botswana, up to 10 at a time are smuggled into South Africa where they are sold as a delicacy to wealthy individuals or exported outside Africa."
The Worlds Heaviest Flying Bird - The Kori Bustard (Gompou in Afrikaans) seen in Pilanesburg National Park South Africa

Ardeotis kori, Kori Bustard

"Ardeotis kori, Kori Bustard - Kansas City Zoo."
South African Photographs: Kori Bustard
This is a Kori Bustard and is slightly bigger than a turkey. It eats a wide variety of animals and plant products, often eating hard materials, such as stones, pieces of bones and even bullet … Read more…
LPJC posted a photo:. Kori bustard flying. Two of these were flying overhead as we were in the western end of Etosha. Though I had hoped for a better photo, I read that these birds rarely take … Read more…
Courting Kori Bustard displaying IMG_8915
Courting Kori Bustard displaying IMG_8915. Another Kori Bustard displaying. I had seen this before but the Ngorogoro Crater provided an excellent chance to photograph it. They puff up a… Read more…
Video:
Commentary:
And both Jesse and I scared Kori bustards into flight while driving [this is an old joke between us–the Kori bustard is the largest flighted bird, but you don’t normally see them flying be… Read more…
The Mega-Avi-Fauna of Africa: Kori Bustards (Ardeotis kori)
The Kori Bustard is a member of the Bustard family (Otididae), a group of birds found throughout Africa, reaching into Europe and Asia. Bustards are currently placed in the order Gruiformes, w… Read more…
A kori bustard – shelters under a small candle pod acacia bush in stark silhouette. We snooze at midday and wake soaked in sweat. We are in the Selinda Reserve, northern Botswana. Yellow gra… Read more…
We saw Zebra, Gazelle, Ostriches and a Kori Bustard. (A very large savanna bird that is over 4 feet tall!). When we arrived, the children were seated in their worship centre, anxious to begin t… Read more…
Wandering where the lions are (Nov. 26, 2008 - Halili, Etosha …
several weird "kori bustard" birds, which looked like a fat goose with a large beak and big head feathers; more random birds, including blue cranes, Egyptian geese, sandgrouse, vultures, and No… Read more…