The Yellow-billed stork (Mycteria ibis), which is sometimes called the wood stork or wood ibis, is adaptive and intelligent. It is also closely related to the American wood stork (Mycteria americana), milky stork (Mycteria cinerea) and painted stork (Mycteria leucocephala). The yellow-billed stork occurs primarily in Eastern Africa, but is widely distributed in areas extending from Senegal and Somalia down to South Africa and in some regions of western Madagascar. During one observation of a mixed species bird colony on the Tana River in Kenya, it was found to be the commonest species there, with 2000 individuals being counted at once. It does not generally migrate far, at least not out of its breeding range; but usually makes short migratory movements which are influenced by rainfall. It makes local movements in Kenya and has also been found to migrate from North to South Sudan with the rainy season. It may also migrate regularly to and from South Africa. However, little is actually known about this bird’s general migratory movements. Due to apparent observed variation in migratory patterns throughout Africa, the yellow-billed stork has been termed a facultative nomad. It may migrate simply to avoid areas where water or rainfall conditions are too high or too low for feeding on prey. Some populations migrate considerable distances between feeding or breeding sites; usually by using thermals to soar and glide. Other local populations have been found to be sedentary and remain in their respective habitats all year round. Its preferred habitats include wetlands, shallow lakes and mudflats, usually 10–40 cm deep, but it usually avoids heavily forested regions in central Africa. It also avoids flooded regions and deep expansive bodies of water because feeding conditions there are unsuitable for their typical grope and stir feeding techniques. This species breeds especially in Kenya and Tanzania. Although it is known to breed in Uganda, breeding sites have not been recorded there. It has been found to breed also in Malakol in Sudan and often inside walled cities in West Africa from Gambia down to northern Nigeria. Still other breeding sites include Zululand in South Africa and northern Botswana, but are rarer below northern Botswana and Zimbabwe where sites are well-watered. Although there is no direct evidence of current breeding in Madagascar, young birds unable to fly have been observed near Lake Kinkony during October. It is a medium-sized stork standing 90–105 cm (35–41 in) tall. The body is white with a short black tail that is glossed green and purple when freshly moulted. The bill is deep yellow, slightly decurved at the end and has a rounder cross-section than in other stork species outside the Mycteria. Feathers extend onto the head and neck just behind the eyes, with the face and forehead being covered by deep red skin. Both sexes are similar in appearance, but the male is larger and has a slightly longer heavier bill. Males and females weigh approximately 2.3 kg (5.1 lb) and 1.9 kg (4.2 lb) respectively. Colouration becomes more vivid during the breeding season. In the breeding season, the plumage is coloured pink on the upperwings and back; the ordinarily brown legs also turn bright pink; the bill becomes a deeper yellow and the face becomes a deeper red. Juveniles are greyish-brown with a dull, partially bare, orange face and a dull yellowish bill. The legs and feet are brown and feathers all over the body are blackish-brown. At fledging, salmon-pink colouration in the underwings begins to develop and after about one year, the plumage is greyish-white. Flight feathers on the tail and wing also become black. Later, the pink colouration typical of adult plumage begins to appear.
