Yellow-billed stork

[2][3] Species within Mycteria display remarkable homologies in behavior (e.g., feeding and courtship) and morphology, with relatively few species-specific variations.

[4] The bill is deep yellow, slightly decurved at the end and with a rounder cross-section than in other stork species outside the Mycteria.

[3] 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.

[4] This species is generally non-vocal, but will utter hissing falsetto screams during social displays in the breeding season.

[4] These storks also engage in bill clattering and an audible “woofing” wing beat at breeding colonies[4] Nestlings make a loud continual monotonous braying call to beg parental adults for food.

[4] It is also the dominant species in large breeding colonies at Lake Manyara and the Ihefu wetlands fringing the Ripera River in Tanzania.

[8] 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.

Due to apparent observed variation in migratory patterns throughout Africa, the yellow-billed stork has been termed a facultative nomad.

[4] Preferred habitats include wetlands, shallow lakes and mudflats, usually 10–40 cm deep[4] but it usually avoids heavily forested regions in central Africa.

[6] It has been found to breed also in Malakol in Sudan[4] and often inside walled cities in West Africa from Gambia down to northern Nigeria.

[4] Although there is no direct evidence of current breeding in Madagascar, young birds unable to fly have been observed near Lake Kinkony during October.

[3] In addition to the snap-bill reflex, the yellow-billed stork also uses a systematic foot stirring technique to sound out evasive prey.

[6] The yellow-billed stork has been observed to follow moving crocodiles or hippopotami through the water and feed behind them, appearing to take advantage of organisms churned up by their quarry.

Breeding is seasonal and appears to be stimulated by the peak of long heavy rainfall[16][17] and resultant flooding of shallow marshes, usually near Lake Victoria.

Kahl's explanation for this trend was that in the dry season, most prey fish are forced to leave the dried-up, deoxygenated marshes that cannot support them and retreat to the deep waters of Lake Victoria where the storks cannot reach them.

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.

This occurs especially on flat extensive marshlands as water levels gradually decrease and concentrate fish sufficiently for the storks to feed on.

Here, the male stands on the potential nesting-site and bends over to gently grasp and release underlying twigs at regular intervals.

One such behaviour is the Balancing Posture,[3] whereby she walks with a horizontal body axis and extended wings toward the male occupying the nesting-site.

[4] As in many other stork species,[21][22] hatching is asynchronous (usually at 1- to 2-day intervals),[4] so that the young in the brood differ considerably in body size at any one time.

This may aid the typical thermoregulatory strategy of the young (common to all stork species)[3] to excrete dilute urine down their legs in response to hot weather.

In one investigation, four adult, hand-reared yellow-billed storks kept in captivity showed typical grope-feeding and foot stirring shortly after they were introduced to bodies of water.

[3] 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.

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.

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.

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.

[3] 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.

[4] However, in East Africa, it is known to be at risk from poaching and habitat reduction despite abundance and population stability[4] and is listed under the African-Eurasian Waterbird Agreement (AEWA).

Vivid colours of breeding plumage, Zambia
Adult in flight, Zambia
Juvenile in flight, Zambia
Flock in a seasonal wetland, Zambia
Mycteria ibis eggs MHNT
Colony of nests in tall trees, Zambia
Stick nests on a tall tree, Zambia