Shoebill

Appearance

The Shoebill is a tall bird, with a typical height range of 110 to 140 cm and some specimens reaching as much as 152 cm. Length from tail to beak can range from 100 to 140 cm and wingspan is 230 to 260 cm.

Weight has reportedly ranged from 4 to 7 kg in the Shoebill. A male will weigh on average around 5.6 kg and is larger than a typical female of 4.9 kg. The signature feature of the species is its huge, bulbous bill, which is straw-colored with erratic grayish markings.

The exposed culmen is 18.8 to 24 cm. The sharp edges in the mandibles help the Shoebill to decapitate their prey and also to discard any vegetation after prey has been caught. As in the pelicans, the upper mandible is strongly keeled, ending in a sharp nail. The dark colored legs are fairly long, with a tarsus length of 21.7 to 25.5 cm.

The Shoebill's feet are exceptionally large, with the middle toe reaching 16.8 to 18.5 cm in length, likely assisting the species in its ability to stand on aquatic vegetation while hunting. The neck is relatively shorter and thicker than other long-legged wading birds such as herons and cranes.

The wings are broad, with a wing chord length of 58.8 to 78 cm, and well-adapted to soaring. At close range, it can be easily identified by its unique features. In flight, if its unique bill cannot be seen, the Shoebill's silhouette resembles that of a stork or condor, but its feathers are a distinctive medium blue-gray. Unusually also, its tail is the same color as its wings. Under poor viewing conditions, its size and wingspan compared to other birds in its habitat can identify it. Its legs, roughly the length of storks, extend straight back far past its tail when in flight. The wing to tail size can't be used for identification; it's similar to several other birds.

Distribution

The Shoebill is distributed in freshwater swamps of central tropical Africa, from southern Sudan through parts of eastern Congo, Rwanda, Uganda and western Tanzania.

Status

The population is estimated at between 5,000 and 8,000 individuals, the majority of which live in swamps in Sudan, Uganda, eastern Democratic Republic of the Congo, and Zambia. BirdLife International have classified it as Vulnerable with the main threats being habitat destruction, disturbance and hunting.

Behavior

The Shoebill is noted for its slow movements and tendency to remain still for long periods, resulting in repeated descriptions of the species as "statue-like". They are quite sensitive to human disturbance and may abandon their nests if flushed by humans. However, while foraging, if dense vegetation stands between it and humans, this wader can be fairly tame.

The Shoebill is attracted to poorly oxygenated waters where fish frequently surface to breathe. Exceptionally for a bird this large, the Shoebill often stands and perches on floating vegetation, making them appear somewhat like a giant jacana, although the similarly-sized and occasionally sympatric Goliath heron is also known to stand on aquatic vegetation.

Habitat

The Shoebill occurs in extensive, dense freshwater marshes. Almost all wetlands that attract the species have undisturbed ''Cyperus papyrus'' and reedbeds of ''Phragmites'' and ''Typha''.

Reproduction

The solitary nature of Shoebills extends to their breeding habits. Nests typically occur at less than 3 nests per square kilometer, unlike herons, cormorants, pelicans and storks which predominantly nest in colonies. The breeding pair of Shoebills vigorously defends a territory of 2 to 4 km2 from conspecifics.

In the extreme north and south of the species' range, nesting starts right after the rains end. In more central regions of the range, it may nest near end of wet season in order to hatch around the beginning of the following wet season. Both parents engage in building the nest on floating platform, after clearing out an area of approximately 3 m across.

The large, flattish nesting platform is often partially submerged in water and can be as much as 3 m deep. The nest itself is about 1 to 1.7 m across. Both the nest and platform are made of aquatic vegetation. In Sudan, the nests apparently was able to support the weight of an adult man, although this was not the case in Zambia.

From one to three white eggs are laid. These eggs measure 80 to 90 mm high by 56 to 61 mm and weigh around 164 g. Incubation lasts for approximately 30 days. Both parents actively brood, shade, guard and feed the nestling, though the females are perhaps slightly more attentive.

Food items are regurgitated whole from the gullet straight into the bill of the young. Shoebills rarely raise more than one chick, but will hatch more. The younger chicks are intended as back-ups in case the eldest dies or is weak.

Fledging is reached at around 105 days and the young birds can fly well by 112 days. However, they are still fed for possibly a month or more after this. It will take the young Shoebills 3 years before they become fully sexually mature.

Food

Shoebills typically feed in muddy waters and, being solitary birds, forage at a minimum distance of 20 m from one another even where relatively densely populated. This species stalks its prey patiently, in a slow and lurking fashion. While hunting, the Shoebill strides very slowly and is frequently motionless. Unlike some other large waders, this species hunts entirely using vision and is not known to engage in tactile hunting.

When prey is spotted, it launches a quick, violent strike. However, depending on the size of the prey, handling time after the strike can exceed 10 minutes. Around 60% of strikes are successful in yielding prey. Frequently water and vegetation is snatched up during the strike and is spilled out from the edges of the mandibles. Occasionally, the activity of hippopotamus may inadvertently benefit the Shoebill, as the huge mammals occasionally force fish to the surface of the water while they are submerged.

Shoebills are largely piscivorous but are assured predators of a considerable range of wetland vertebrates. Preferred prey species have reportedly included Marbled lungfish and Senegal Bichir as well as various ''Tilapia'' species and catfish, the latter mainly in the genus ''Clarias''. Other prey eaten by this species has included frogs, water snakes, Nile monitors and baby crocodiles. More rarely, turtles, snails, rodents and small waterfowl have reportedly been predated.