African sacred ibis
The African sacred ibis (Threskiornis aethiopicus) is a species of ibis, a wading bird of the family Threskiornithidae. It is native to much of Africa, as well as small parts of Iraq, Iran and Kuwait.[1] It is especially known for its role in Ancient Egyptian religion, where it was linked to the god Thoth. The species is currently extirpated from Egypt.
Taxonomy[edit]
It is very closely related to the black-headed ibis and the Australian white ibis, with which it forms a superspecies complex, so much so that the three species are considered conspecific by some ornithologists.[2] In mixed flocks these ibises often hybridise.[3] The Australian white ibis is often called the sacred ibis colloquially.[4]
Although known to the ancient civilisations of Greece, Rome and especially Africa, ibises were unfamiliar to western Europeans from the fall of Rome until the 19th century, and mentions of this bird in the ancient works of these civilisations were supposed to describe some type of curlew or other bird, and were thus translated as such.[5] In 1758, Linnaeus was convinced that the ancient authors were describing a cattle egret (Bubulcus ibis), which he thus described as Ardea ibis.[6] Following the work of Mathurin Jacques Brisson, who calls it Ibis candida in 1760, in the 12th edition of his Systema Naturae of 1766 Linnaeus classifies it as Tantalus ibis.[7][8] These were also unfamiliar birds that did not occur in Europe at the time, in English in these times called the 'Egyptian ibis' by Latham, and the 'emseesy' or 'ox-bird' by George Shaw.[9]
In 1790, John Latham provided the first unambiguous modern scientific description of the sacred ibis as Tantalus aethiopicus, mentioning James Bruce of Kinnaird who called it 'abou hannes' in his writings describing his travels in Sudan and Ethiopia, and also described Tantalus melanocephalus of India.[9]
Georges Cuvier named it Ibis religiosus in his Le Règne Animal of 1817.[10]
In 1842, George Robert Gray reclassified the bird under the new genus Threskiornis, because the type of the genus Tantalus was designated as to be the wood stork, also formerly known as the wood ibis or wood pelican, and Gray decided these birds could not be classified in the same genus.[11][12]
In a comprehensive review of plumage patterns by Holyoak in 1970, it was noted that the three taxa were extremely similar and that the Australian birds resembled Threskiornis aethiopicus in adult plumage and T. melanocephalus in juvenile plumage, he thus proposed they all be considered part of a single species T. aethiopicus. At the time, this was generally accepted by the scientific community; however, in 'The Birds of the Western Palearctic' compendium of 1977, Roselaar advocated splitting the group into four species, recognising T. bernieri, based again on the then known geographical morphological differences.[13]
In 1990, Sibley & Monroe, in the general reference 'Distribution and Taxonomy of Birds of the World' followed Roselaar in recognising four species, which they repeated in 'A World Checklist of Birds' of 1993.[14][15]
This taxon being split from T. melanocephalus and T. molucca was further advocated by another morphological study by Lowe and Richards in 1991, where they looked at plumage, bill and neck sack morphology and used many more skins. They concluded that the differences were such to merit separate species status for the three taxa, especially as they could find no intergradation in morphological characters in possible contact zones in SE Asia. They also cite observed differences in courtship displays between the Australian and African birds. Based on these characteristics they recommended the Madagascan birds T. bernieri and T. abbotti be considered a subspecies of T. aethiopicus.[13]
Distribution[edit]
Native[edit]
The sacred ibis breeds in Sub-Saharan Africa and southeastern Iraq. A number of populations are migrant with the rains; some of the South African birds migrate 1,500 km as far north as Zambia, the African birds north of the equator migrate in the opposite direction. The Iraqi population usually migrates to southwestern Iran, but wandering vagrants have been seen as far south as Oman (rare, but regular) and as far north as the Caspian coasts of Kazakhstan and Russia (before 1945).[19][20][21][22]
Ecology[edit]
Habitat[edit]
The African sacred ibis occurs in marshy wetlands and mud flats, both inland and on the coast. It preferably nests on trees in or near water. It feeds wading in very shallow wetlands or slowly stomping in wet pastures with soft soil. It will also visit cultivation and rubbish dumps.[29][53]
Diet[edit]
The species are predators which feed primarily by day, generally in flocks. The diet consists of mainly insects, worms, crustaceans, molluscs and other invertebrates, as well as various fish, frogs, reptiles, small mammals and carrion.[16][53][64] It may also probe into the soil with its long beak for invertebrates such as earthworms.[64] It even sometimes feeds on seeds.[65]
Sacred ibises were observed to occasionally feed on the contents of pelican eggs broken by Egyptian vultures in the mixed colonies of the ibises, cormorants, pelicans and Abdim's storks at Lake Shala in Ethiopia.[66] On Central Island in Lake Turkana sacred ibises were noted to incidentally eat Nile crocodile eggs excavated by Nile monitors.[28] Most recently, in 2006, observations were reported from a large mixed colony on Bird Island (called Penguin Island in the article) in South Africa, where 10,000 pairs of gannets nested, together with 4800 pairs of Cape cormorant and other species such as gulls and jackass penguin. Within a period of 3 years, a few specialized sacred ibis individuals out of the 400 that roosted on the island had fed on at least 152 eggs of the cormorant (other species were even more ovivorous).[67]
In a study of pellets and stomachs contents of nestlings in the Free State, South Africa, food is mostly reported to consist of frogs (mainly Amietia angolensis and Xenopus laevis), Potamonautes warreni crabs, blow fly maggots, Sphingidae caterpillars, and adult beetles. During the first 10 days of life nestlings fed mainly on crabs and beetles, and later mainly on Sphingidae caterpillars and more beetles. The breeding colony collected different (proportions of) prey the subsequent year.[68] The food of one one‐month old nestlings at Lake Shala, Ethiopia, consisted of beetle larvae, caterpillars and beetles.[66] In France, adult ibises fed largely on the invasive crayfish Procambarus clarkii, for nestlings larvae of Eristalis species are important.[28][53]
In France, they sometimes supplement their diet by feeding at rubbish tips in the winter.[28]
Predators[edit]
The most important predator of nestlings of the sacred ibis in Kenya is the African fish eagle, which preferentially searches for the largest (sub-)colonies to attack, but in Ethiopia and South Africa it poses less of a threat.[29]
Diseases[edit]
This species was reported to be susceptible to avian botulism in a list of dead animals found around a man-made lake in South Africa which tested positive for the pathogen in the late 1960s and early 1970s.[69] During a large scale mortality of Cape cormorants from avian cholera in 1991 in western South Africa, small numbers of sacred ibis were killed.[53] The new species Chlamydia ibidis was isolated from feral sacred ibis in France in 2013; it infected 6–7 of the 70 birds tested.[70]
In 1887, the Italian scientist Corrado Parona reported a 3 cm Physaloptera species of nematode in the orbital cavity of a sacred ibis collected in Metemma, Abyssinia (now Ethiopia) in 1882. He thought it was perhaps a new species, as it differed morphologically from earlier seen worms. A single adult female was recovered, and it has never been seen again. As the Physaloptera species infecting birds are generally parasites of the intestines of raptors; it might be an artefact, or perhaps a misidentification, or possibly a dead-end host infection.[71][72][73][74] The digenean trematode Patagifer bilobus, a fluke, has been reported from sacred ibis in Sudan before 1949. It lives in the small intestine of this species, among numerous other ibises, spoonbills, and a few other waterfowl. It has a complicated life history involving three hosts: the eggs hatch in fresh water where they infect a ram's horn snail in which they multiply and produce cercariae, which exit and encyst in a larger snail such as a Lymnaea, waiting to be eaten by a bird.[75]
Eggs of the Threskiornis aethiopicus
The species usually breeds once per year in the wet season. Breeding season is from March to August in Africa, from April to May in Iraq.[16] It builds a stick nest, often in a baobab tree. The bird nests in tree colonies, often with other large wading birds such as storks, herons, African spoonbills, African darters, cormorants. It may also form single-species groups on offshore islands or abandoned buildings. Island nests are often made on the ground. Large colonies consist of numerous subcolonies and can number 1000 birds.[29][64]
Females lay one to five eggs per season, incubated by both parents for 21 to 29 days.[17] After hatching, one parent continuously stays at the nest for the first seven days.[16] Chicks fledge after 35 to 40 days and are independent after 44 to 48 days, reaching sexual maturity one to five years after hatching.[17]