Zephyr

Description

Geographic Range

Shoebill or whale-headed storks are endemic to Africa and inhabit the east-central part of the continent. The main populations are found in southern Sudan (mainly in the White Nile Sudd), the wetlands of northern Uganda and western Tanzania and the Bangweulu swamp of northeastern Zambia. Smaller populations occupy eastern Zaire and Rwanda. This bird’s range usually coincides with that of papyrus and lungfish.

Habitat

Shoebill storks inhabit freshwater swamps and extensive, dense marshes. They are often found in areas of flood plain interspersed with undisturbed papyrus and reedbeds. When shoebill storks are in an area with deep water, a bed of floating vegetation is a requirement. They are also found where there is poorly oxygenated water. This causes the fish living in the water to surface for air more often, increasing the likelihood a shoebill stork will successfully capture it.

Physical Description

Large, somewhat frightful looking birds, shoebill storks stand 110 to 140 cm tall. Males are larger than females and have longer bills. The plumage is salty blue-grey overall with a darker grey head. The primaries are black-tipped and secondary’s have a greenish tint. The underparts are a lighter shade of grey. Adult breeding plumage does not differ from non-breeding plumage. On the back of the head is a small tuft of feathers that can erect in a crest. A newly hatched shoebill stork is covered in silvery-grey silky down and juveniles are a slightly darker shade of grey than adults. The bill is the most prominent feature of shoebill storks and resembles a wooden shoe. It is an enormous structure ending in a sharp, curved hook. The color of the bill is yellowish with blotchy dark spots. The mandibles have sharp edges that aid in capturing and eating prey. The eyes are large and yellowish or grayish-white in color. The legs are long and blackish. The toes are extremely long and completely divided with no webbing between them.

• Range length110 to 140 cm43.31 to 55.12 in

Reproduction

Shoebill storks form monogamous pairs for breeding.

Shoebill storks are solitary breeders and have territories measuring approximately 3 square kilometers. In the breeding season, these birds are very territorial and will defend the nest against any predators or competitors. Breeding time varies depending on location, but usually coincides with the start of the dry season. The reproductive cycle from nest building to fledging spans a period of 6 to 7 months. An area with a 3 meter diameter is trampled and cleared for the nest. The nest is located on either a small island or on a mass of floating vegetation. Nesting material, such as grass, is weaved on the ground, forming a large structure of about 1 meter in diameter. One to three, normally two, flaky whitish eggs are laid. However, by the end of the breeding cycle usually only one chick remains due to predation or food availability. The incubation period is about 30 days. After hatching, adult shoebill storks must feed the chicks regurgitated food at least 1 to 3 times per day and up to 5 to 6 times per day as the chick grows older. Parents hold out food to the chicks, which must feed themselves.

• Breeding interval: Shoebill storks breed once yearly.
• Range eggs per season: 1 to 3
• Average time to hatching: 30 days
• Average fledging age: 95 days
• Average time to independence: 125 days

Shoebill storks are monogamous breeders and both parents participate in every aspect of nest building, incubation, and chick rearing. Egg-watering is a behavior that has been recorded on many occasions and that is also observed in true storks. In order to keep the eggs cool, the adult shoebill will get a mouthful of water and pour it over the nest. It will also get mouthfuls of wet grass to place around the eggs and will roll and turn over the eggs with its feet or bill. The dousing behavior and also shading will continue after the eggs hatch until the feathers of the chicks are fully developed.

The development of shoebill storks is a slow process compared to most other birds. Feathers do not fully develop until about 60 days and the birds fledge at 95 days. However, the young cannot fly until about 105 to 112 days. Parents continue to feed the young for about one month after fledging. After this point, young shoebill storks are totally independent of their parents.

Lifespan/Longevity

Shoebill storks live to almost 36 years in the wild.

• Range lifespan: Status – wild35.7 (high) years
• Average lifespan: Sex – male, Status – captivity 35.7 years
• Average lifespan: Status – captivity 36.0 years

Behavior

Shoebill storks are and are never found in groups. Only when food is in short supply will shoebill storks forage near each other. Often, the male and female of a breeding pair will forage on opposite sides of their territory. Adults use gular-fluttering in order to keep cool.

Shoebill storks are non-migratory as long as good foraging conditions exist. However, in some areas of their range, they will make seasonal movements between nesting and feeding zones. Shoebill storks soar on thermals and are often seen soaring above their territory during the day. In flight, the neck is retracted. Shoebill storks are very docile with humans. Researchers studying these birds have been able to come within 6 feet of a shoebill stork on its nest. The shoebill stork will not threaten humans, but will only stare right back at them.

Communication and Perception

Shoebill storks are usually silent, but will often participate in bill-clattering, a behavior characteristic of true storks. Adults will often do this when greeting each other at the nest, but young shoebills also perform the bill-clatter. Adults will also make a whining or “mooing” noise and young will make a hiccupping noise especially when begging for food.

The principal senses used during hunting are vision and hearing. In order to facilitate binocular vision, shoebill storks hold their heads and bills vertically downward against the breast.

Food Habits

Shoebill storks spend most of their time foraging in aquatic environments. On occasion, they will also consume frogs, monitor lizards, turtles, young crocodiles, mollusks and carrion. The most suitable area for catching prey is one with shallow water and tall vegetation to camouflage the bird as it stalks prey. If the water is deep, a firm, floating platform of vegetation must be present in order to hunt.

The two mechanisms by which shoebill storks hunt are “stand and wait” and “wade and walk slowly.” When a prey item is spotted, shoebill storks will begin the “collapse”. The head and neck quickly stretch forward into the water causing the bird to over-balance and collapse forwards and downwards. After a collapse, a shoebill stork cannot immediately perform a second collapse. It must regain its balance and start from the standing position again. Along with the prey, a mouthful of vegetation is also collected. In order to expel the vegetation, shoebill storks sway their heads from side to side while keeping hold of the prey. Before swallowing, the prey is usually decapitated.