The shoebill (Balaeniceps rex) also known as whalehead or shoe-billed stork, is a very large stork-like bird. It derives its name from its massive shoe-shaped bill. Although it has a somewhat stork-like overall form and has previously been classified in the order Ciconiiformes, its true affiliations with other living birds is ambiguous. Some authorities now reclassify 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.
The shoebill was only classified in the 19th century when some skins were brought to Europe. It was not until years later that live specimens reached the scientific community. However, the bird was known to both ancient Egyptians and Arabs. 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) or the herons (based on biochemical evidence; Hagey et al., 2002). A recent DNA study suggests they are part of the Pelecaniformes.
The dispute has turned out to be mainly one of where to draw the boundary between Ciconiiformes and Pelecaniformes, or whether to draw it at all. Since cormorants and relatives are probably not actually Pelecaniformes, a solution adopted by some modern authors is to merge the “core” Pelecaniformes with the Ciconiiformes. The shoebill and the hammerkop (Scopus umbretta) are the “missing links” that connect pelicans and storks, and including the pelican lineage in the Ciconiiformes expresses this more adequately than other treatments do.
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.
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 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 shoebill is distributed in freshwater swamps of central tropical Africa, from southern Sudan through parts of eastern Congo, Rwanda, Uganda and western Tanzania. 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.
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.
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 (Ardea goliath) is also known to stand on aquatic vegetation. Shoebills typically feed in muddy waters and, being solitary birds, forage at a minimum distance of 20 m (66 ft) 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 (Protopterus aethiopicus) and Senegal bichir (Polypterus senegalus) 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 (Varanus niloticus) and baby crocodiles. More rarely, turtles, snails, rodents and small waterfowl have reportedly been eaten. There exists a single report of shoebills feeding on lechwe (Kobus leche) calves, although 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 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 consisted of the catfish Clarias gariepinus (syn. C. mossambicus) and water snakes. In Uganda, lungfish and catfish were mainly fed to the young.