The
shoebill (
Balaeniceps rex) also known as
whalehead, 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 the
Pelecaniformes. The adult is mainly grey while the juveniles are browner. It lives in tropical east
Africa in large swamps from
Sudan to
Zambia.
[2]
Taxonomy and systematics
Molecular studies have found the
hamerkop to be the closest relative of the shoebill.
The shoebill was known to both ancient
Egyptians and
Arabs[citation needed]
but was not classified until the 19th century, after skins and
eventually live specimens were brought to Europe. Traditionally 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". More recently, the shoebill has been considered to be
closer to the
pelicans (based on anatomical comparisons)
[3] or the
herons (based on biochemical evidence; Hagey
et al., 2002).
[4]
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 microglobular material over the crystalline shells.
[5] A recent DNA study reinforces their membership of the Pelecaniformes.
[6]
So far, two fossil 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.
Description
The shoebill's conspicuous bill is its most well-known feature.
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).
[7][8] 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).
[9] 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.
[9]
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 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 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.
[2]
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.
[9]
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).
[9]
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.
Identification
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-grey. Also unusual, its tail is the same colour as its
wings. Under poor viewing conditions, its size and wingspan can
distinguish it from other birds in its habitat. Its legs, roughly the
length of storks', extend straight back far past its tail when in
flight. The wing to tail size cannot be used for identification; it is
similar to those of several other birds.
A shoebill at a zoo, (video)
Distribution and habitat
The shoebill is distributed in freshwater swamps of central tropical Africa, from southern
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 adjacent areas of the south Sudan; 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.
The shoebill is non-migratory with limited seasonal movements due to
habitat changes, food availability and disturbance by humans.
[9]
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.
[9]
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 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 typically feed
in muddy waters and, 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.
[9]
Shoebills are largely
piscivorous but are assured predators of a considerable range of wetland vertebrates. Preferred prey species have reportedly included
marbled lungfish (
Protopterus aethiopicus) and
Senegal bichir (
Polypterus senegalus) and 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 (
Varanus niloticus) and baby
crocodiles. More rarely,
turtles,
snails,
rodents and small
waterfowl have reportedly been eaten. There is a single report of shoebills feeding on
lechwe (
Kobus leche)
calves, but this would need confirmation. Given its sharp-edged beak,
huge bill and wide gape, the shoebill can hunt large prey, often
targeting prey bigger than is taken by other large wading birds. Fish
eaten by this species are commonly in the range of 15 to 50 cm (5.9 to
19.7 in) long and weigh around 500 g (1.1 lb), though lungfish of as
much as 1 m (3.3 ft) have been attacked. Snakes preyed upon are commonly
from 50 to 60 cm (20 to 24 in) long. In the
Bangweulu Swamps of
Zambia, the main prey items fed to young by the parents were the catfish
Clarias gariepinus [10](
syn. C. mossambicus) and water snakes. In
Uganda, lungfish and catfish were mainly fed to the young.
[9] The big beak is sometimes used to dig into pond-bottom mud to extract
lungfish from their
aestivation burrows.
Breeding
The solitary nature of shoebills extends to their breeding habits.
Nests typically occur at less than three nests per square kilometre,
unlike
herons,
cormorants,
pelicans and
storks which predominantly nest in colonies. The breeding pair of shoebills vigorously defends a territory of 2 to 4 km
2 (0.77 to 1.54 sq mi) 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
(9.8 ft) across. The large, flattish nesting platform is often partially
submerged in water and can be as much as 3 m (9.8 ft) deep. The nest
itself is about 1 to 1.7 m (3.3 to 5.6 ft) wide. Both the nest and
platform are made of aquatic vegetation. In Sudan, the nests apparently
were able to support the weight of an adult man, although this was not
the case in Zambia.
[citation needed]
From one to three white eggs are laid. These eggs measure 80 to 90 mm
(3.1 to 3.5 in) high by 56 to 61 mm (2.2 to 2.4 in) and weigh around
164 g (5.8 oz). 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 three years before they become fully
sexually mature.
[9]
Voice
The shoebill is normally silent, but they perform bill-clattering displays at the nest.
[2] When engaging in these displays, adult birds have also been noted to utter a
cow-like
moo
as well as high-pitched whines. Both nestlings and adults engage in
bill-clattering during the nesting season as a means of communication.
When young are begging for food, they call out with a sound uncannily
like human hiccups. In one case, a flying adult bird was heard uttering
hoarse croaks, apparently as a sign of aggression at a nearby
marabou stork (
Leptoptilos crumeniferus).
[9]
Status and conservation
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.
[11] There is also a viable population in the Malagarasi wetlands in Tanzania.
[12] BirdLife International has classified it as
Vulnerable with the main threats being
habitat destruction, disturbance and hunting.
Relationship to humans
This species is considered to be one of the five most desirable birds in Africa by ornithologists.
[13] There are Egyptian images depicting the shoebill, while the Arabs referred to the bird as
abu markub, which means
one with a shoe, a reference to the bird's distinctive bill.
[citation needed]
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