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The shoebill (Balaeniceps rex) also known as whale head, whale-headed stork, or shoebill stork, is a very large stork-like bird. It derives its name from its enormous shoe-shaped bill. It has a somewhat stork-like overall form and has previously been classified with the storks in the order Ciconiiformes based on this morphology. However, genetic evidence places it with pelicans and herons in the Pelecaniformes. The adult is mainly grey while the juveniles are more brown. It lives in tropical east Africa in large swamps from South Sudan to Zambia
The shoebill is a tall bird, with a typical height range of 110 to 140 cm (43 to 55 in) and some specimens reaching as much as 152 cm (60 in). Length from tail to beak can range from 100 to 140 cm (39 to 55 in) and wingspan is 230 to 260 cm (7 ft 7 in to 8 ft 6 in). Weight has reportedly ranged from 4 to 7 kg (8.8 to 15.4 lb) A male will weigh on average around 5.6 kg (12 lb) and is larger than a typical female of 4.9 kg (11 lb). The signature feature of the species is its huge, bulbous bill, which is straw-coloured with erratic greyish markings. The exposed culmen (or the measurement along the top of the upper mandible) is 18.8 to 24 cm (7.4 to 9.4 in), the third longest bill among extant birds after pelicans and large storks, and can outrival the pelicans in bill circumference, especially if the bill is considered as the hard, bony keratin portion.
As in the pelicans, the upper mandible is strongly keeled, ending in a sharp nail. The dark coloured legs are fairly long, with a tarsus length of 21.7 to 25.5 cm (8.5 to 10.0 in). The shoebill's feet are exceptionally large, with the middle toe reaching 16.8 to 18.5 cm (6.6 to 7.3 in) 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 (23.1 to 30.7 in), and well-adapted to soaring.
The shoebill was known to ancient Egyptians but was not classified until the 19th century, after skins
and eventually live specimens were brought to Europe. John Gould described it in 1850, giving it the name Balaeniceps
rex. The genus name comes from the Latin words balaena "whale", and caput "head",
abbreviated to -ceps in compound words.
Traditionally considered as allied with the storks (Ciconiiformes), it was retained there in the Sibley-Ahlquist taxonomy which lumped a massive number of unrelated taxa into their
"Ciconiiformes". Based on osteological evidence, the suggestion of a
pelecaniform affinity was made in 1957 by Patricia Cottam. Microscopic analysis of eggshell structure by Konstantin
Mikhailov in 1995 found that the eggshells of shoebills closely resembled those
of other Pelecaniformes in having a covering of thick micro globular
material over the crystalline shells. In 2003, the shoebill was again suggested
as closer to the pelicans (based on anatomical comparisons or the herons (based on biochemical evidence) A 2008
DNA study reinforces their membership of the Pelecaniformes.
So far, two fossilized relatives of the shoebill have been
described: Goliathia from the early Oligocene of Egypt and Paludavis from
the Early Miocene of the same country. It has been
suggested that the enigmatic African fossil bird Eremopezus was a relative too, but the evidence for
that is unconfirmed. All that is known of Eremopezus is that
it was a very large, probably flightless bird with a flexible foot, allowing it
to handle either vegetation or prey.
The skull
The plumage of adult birds is blue-grey with darker slaty-grey flight feathers. The breast presents some elongated feathers,
which have dark shafts. The juvenile has a similar plumage colour, but is a
darker grey with a brown tinge. When they are first born, shoebills have a more modestly-sized
bill, which is initially silvery-grey. The bill becomes more noticeably large
when the chicks are 23 days old and becomes well developed by 43 days.
Flight pattern
Its wings are held flat while soaring and, as in the pelicans and the storks of the genus Leptoptilos, the shoebill flies with its neck retracted. Its flapping rate, at an estimated 150 flaps per minute, is one of the slowest of any bird, with the exception of the larger stork species. The pattern is alternating flapping and gliding cycles of approximately seven seconds each, putting its gliding distance somewhere between the larger storks and the Andean condor (Vultur gryphus). When flushed, shoebills usually try to fly no more than 100 to 500 m (330 to 1,640 ft). Long flights of the shoebill are rare, and only a few flights beyond its minimum foraging distance of 20 m (66 ft) have been recorded.
Distribution and
habitate
The shoebill is distributed in freshwater swamps of central
tropical Africa, from southern Sudan and South Sudan through parts of eastern Congo, Rwanda, Uganda, western Tanzania and northern Zambia. The species is most numerous in the West Nile sub-region and South Sudan (especially the Sudd, a main stronghold
for the species); it is also significant in wetlands of Uganda and western
Tanzania. More isolated records have been reported of shoebills in Kenya, the Central African Republic, northern Cameroon, south-western Ethiopia, Malawi. Vagrant strays to the Okavango Basin, Botswana and the upper Congo River have also been sighted. The distribution of this species
seems to largely coincide with that of papyrus and lungfish. 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. The shoebill is non-migratory with limited seasonal
movements due to habitat changes, food availability and disturbance by humans
Petroglyphs from Oued Djerat, eastern Algeria, show that the shoebill occurred during the Early Holocene much more to the north, in the wetlands
that covered the present-day Sahara Desert at that time.
The shoebill occurs in extensive, dense freshwater marshes. Almost all wetlands that attract the species have
undisturbed Cyperus papyrus and reed beds of Phragmites and Typha. Although their distribution largely seems to correspond with
the distribution of papyrus in central Africa, the species seems to avoid pure
papyrus swamps and is often attracted to areas with mixed vegetation. More rarely,
the species has been seen foraging in rice fields and flooded plantations.
Behaviour and ecology
The shoebill is noted for its slow movements and tendency to
stay still for long periods, resulting in 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 such as swamps, marshes and
bogs 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 (Ardea goliath) is also known to
stand on aquatic vegetation. Shoebills, being solitary, forage at 20 m
(66 ft) or more 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
yield prey. Frequently water and vegetation is snatched up during the strike
and is spilled out from the edges of the mandibles. The activity of hippopotamus may inadvertently benefit the shoebill, as submerged
hippos occasionally force fish to the surface.
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