Yellow-billed stork

The yellow-billed stork lies within the genus Mycteria along with three other extant species: the wood stork (M. americana), the milky stork (M. cinerea) and the painted stork (M. leucocephala). Species within Mycteria display remarkable homologies in behavior (e.g., feeding and courtship) and morphology, with relatively few species-specific variations. ==Description==

This medium-sized stork stands tall. Its body is white with a short black tail that is glossed green and purple when freshly moulted. 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 are blackish-brown all over. 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 appears. These storks walk with a high-stepped stalking gait on the ground of shallow water. Their approximate walking rate has been recorded as 70 steps per minute. They fly with alternating flaps and glides, with the speed of their flaps averaging 177–205 beats per minute. They usually flap only for short journeys and often fly in a soaring and gliding motion over several kilometres for locomotion between breeding colonies or roosts and feeding sites. By soaring on thermals and gliding by turns, they can cover large distances without wasting much energy. On descending from high altitudes, this stork has been observed to dive deeply at high speeds and flip over and over from side to side, hence showing impressive aerobatics. It even appears to enjoy these aerial stunts. This species is generally non-vocal, but will utter hissing falsetto screams during social displays in the breeding season. These storks also engage in bill clattering and an audible "woofing" wing beat at breeding colonies Nestlings make a loud continual monotonous braying call to beg parental adults for food. ==Distribution and habitat==

The yellow-billed stork occurs primarily in Eastern Africa, but is widely distributed in areas extending from Senegal and Somalia down to South Africa 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. The species does not generally migrate far, at least not outside its breeding range; but does usually make 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. 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. ==Behaviour and ecology==

Diet and feeding This stork's diet mainly comprises small, freshwater fish of about 60-100mm length which they swallow whole. They also feed on crustaceans, worms, aquatic insects, frogs and occasionally small mammals and birds. and although the corresponding reflex in the yellow-billed stork has not been quantitatively measured, Feeding lasts for only a short time before the bird obtains its requirements and proceeds to rest again. and resultant flooding of shallow marshes, usually near Lake Victoria. However, fish move back up the streams on the onset of rain and spread out over the marshes to breed, where they become accessible to the storks. By nesting at this time and providing that the rains do not end pre-maturely, the storks are guaranteed a plentiful food supply for their young. and western and eastern Kenya. Rainfall may cause local flooding and hence ideal feeding conditions. and average clutch size has been recorded as 2.5. hatching is asynchronous (usually at 1- to 2-day intervals), especially on hot days. This may aid the typical thermoregulatory strategy of the young (common to all stork species) but the yellow-billed stork is sometimes the only occupant species of a nesting site. Nest building takes up to 10 days. The nest may be in diameter and thick. Other behaviours Despite their gregariousness during breeding, most individuals generally ignore each other outside nesting-sites; although some hostile encounters may occur. Some of these encounters involve one individual showing an unambiguous attack or escape response if there is a large difference in social status between the two individuals. However, if two individuals are equally matched, they slowly approach each other and show a ritualised display called the Forward Threat. Here, one individual holds its body forward horizontally and retracts the neck so that it touches the crown, with the tail cocked at 45 degrees and all feathers erect. It approaches the opponent and points its bill at it, sometimes gaping. If the opponent does not capitulate, the attacker may grab at it with its bill and the two may briefly spar with their bills until one retreats in an erect stance with compressed plumage. Hostility can also arise between opposite sexes when a female approaches a male on a potential nest site. Both sexes may display a similar aforementioned Forward Threat, but clatter their bills after grabbing with them at the other stork and extend their wings to maintain balance. Another hostile behaviour between sexes is the Snap Display, whereby they snap horizontally with their bills while standing upright. This may occur during and immediately after pair formation, but subsides later in the breeding cycle as the male and female become familiar with each other and it eventually disappears. Nestlings show remarkable behavioural transformations at 3 weeks of age. During the constant parental attendance before this time, the young show little fear or aggression in response to intruders (such as a human observer), but are found to merely crouch low and quietly in the nest. After this time, when both parents go foraging and leave the young in the nest, a nestling shows strong fear in response to an intruder. It either attempts to climb out of the nest to escape or acts aggressively toward the intruder. ==Threats and survival==

As well as being abundant and widespread, the yellow-billed stork also appears tolerant of short-term natural habitat changes. Nevertheless, the overall population is not currently considered to be threatened with serious decline, Eggs may be also at risk of predation by African fish eagles. At one colony in Kisumu, Kenya, approximately 61% of eggs counted between all nests hatched and 38% were predated by fish eagles. The success rate of fledglings was only 0.33 young per nest. However, increased egg predation by fish eagles has been reported to be linked to decline in fish stocks in the Winam Gulf. ==In culture or relationships to humans==

The yellow-billed stork has appeared on postage stamps in several African countries. ==Status==

This species is evaluated as Least Concern for several reasons. First, population trend appears to be decreasing but this decrease is not believed to rapidly approach thresholds for Vulnerable under the population trend criterion. Its range is also very large and does not approach threshold for Vulnerable under range size criterion. Finally, although there have been no official population size estimates, the population is known to be very large and so does not approach thresholds for Vulnerable under population size criterion. ==Gallery==

File:Yellow Billed Story Yawning.jpg|Immature at Maasai Mara National Reserve File:Yellow-billed Stork RWD5.jpg|Storks sometimes rest on their hocks (analogous to a human's heels) File:Yellow-billed stork.jpg|Juveniles have grey backs, mature birds have white backs File:Yellow-billed stork fishing.jpg|Fishing in shallow water File:Yellowbilled stork00.jpg|Juvenile File:Mycteria ibis -Lake Nakuru National Park, Kenya -four-8.jpg|Flock at Lake Nakuru National Park, Kenya File:Nimmersatt (Mycteria ibis)- Weltvogelpark Walsrode 2011.jpg|Weltvogelpark Walsrode, Germany File:Yellow-billed stork kazinga.jpg|With a Nile crocodile at Kazinga Channel, Uganda File:Tántalo africano (Mycteria ibis), parque nacional de Chobe, Botsuana, 2018-07-28, DD 73.jpg|Chobe National Park, Botswana File:Yellow billed stork.jpg|On the bank of a river File:Yellow-billed stork (Mycteria ibis).jpg|Ngorongoro, Tanzania File:חסידן אפריקאי - חסידה צהובת מקור.jpg|Yellow-Billed stork ==References==