An endangered migratory bird found in barren and rocky habitats
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The northern bald ibis, hermit ibis, or Waldrapp (Geronticus eremita) is a migratory Old World ibis found in open areas such as grasslands, rocky mountains, and semi-deserts, often close to running water. This glossy black ibis, which, unlike many members of the ibis family, is non-wading, has an unfeathered red face and head, and a long, curved red bill. It breeds colonially on coastal or mountain cliff ledges, where it typically lays two to three eggs in a stick nest, and feeds on lizards, insects, and other small animals.
The northern bald ibis was once widespread across the Middle East, northern Africa, southern and central Europe, with a fossil record dating back at least 1.8 million years. It disappeared from Europe over 300 years ago, although reintroduction programmes in the region are underway. In 2019 there were about 700 wild birds remaining in southern Morocco, and fewer than 10 in Syria, where it was rediscovered in 2002 but where their number declined in the following years, maybe to zero.
To combat these low numbers, reintroduction programs have been instituted internationally in recent times, with a semi-wild breeding colony in Turkey which counted almost 250 birds in 2018 as well as sites in Austria, Italy, Spain, and northern Morocco. These programmes and the natural growth in Morocco from about 200 birds in the 1990s helped to downlist the northern bald ibis from Critically Endangered to Endangered on the IUCN Red List in 2018. There are about 2000 northern bald ibises living in captivity.
The long-term decline in Europe has been linked to hunting and eating them, especially the fledglings. Because of the slow reproduction of the ibises this may lead to local extinction.
Taxonomy.
The ibises are gregarious, long-legged wading birds with long down-curved bills. Along with the spoonbills they form one subfamily within the family Threskiornithidae. The northern bald ibis' closest relative, and the only other member of the genus, is the southern bald ibis, "G. calvus", of southern Africa. The two "Geronticus" species differ from other ibises in that they have unfeathered faces and heads, breed on cliffs rather than in trees, and prefer arid habitats to the wetlands used by their relatives.
The northern bald ibis was described and illustrated by Swiss naturalist Conrad Gesner in his "Historiae animalium" in 1555, and given the binomial name "Upupa eremita" by Carl Linnaeus in his 1758 "Systema Naturae". It was moved to its current genus by the German herpetologist Johann Georg Wagler in 1832. This species has an interesting history of description, oblivion and rediscovery.
The species probably split into two distinct populations at least 400 years ago and, since then, the two populations have been diverging morphologically, ecologically, and genetically; nevertheless, the Turkish and Moroccan populations of this ibis are not currently classed as separate subspecies. One consistent difference between the eastern and western birds is a single mutation in the cytochrome b gene of their mitochondrial DNA.
Fossils of the northern bald ibis have been found at a Holocene (c. 10,000 years ago) site in southern France, in middle Pleistocene (c. 900,000 years ago) strata in Sicily, and in Pliocene-Pleistocene boundary (c. 1.8 million years ago) deposits on the Mediterranean coast of Spain. What appears to be an ancestral form, "Geronticus balcanicus", was found in the late Pliocene of Bulgaria, further illustrating the early widespread presence of this genus in Europe, and suggesting that "Geronticus eremita" may have originated in southeastern Europe or the Middle East.
Etymology.
The genus name, "Geronticus", is derived from the Ancient Greek : gérōn, meaning "old man" and refers to the bald head of the aged. The species name "eremita" is Late Latin for "hermit", from the : erēmía, meaning "desert", and refers to the arid habitats inhabited by this species. The alternative common name "Waldrapp" is German for "forest raven", the equivalent of the Latin "Corvo sylvatico" of Gesner, adapted as "Corvus sylvaticus" by Linnaeus.
Description.
The northern bald ibis is a large, glossy black bird, long with a wingspan and an average weight of . The plumage is black, with bronze-green and violet iridescence, and there is a wispy ruff on the bird's hind neck. The face and head are dull red and unfeathered, and the long, curved bill and the legs are red. In flight, this bird has powerful, shallow, and flexible wing beats. It gives guttural "hrump" and high, hoarse "hyoh" calls at its breeding colonies, but is otherwise silent.
The sexes are similar in plumage, although males are generally larger than females, and, as with other ibises that breed in colonies, have longer bills. The longer-billed males are more successful in attracting a mate. The downy chick has uniformly pale brown plumage, and the fledged juvenile resembles the adult except that it has a dark head, light grey legs, and a pale bill. The unfeathered areas of the young bird's head and neck gradually become red as it matures. Moroccan birds have a significantly longer bill than Turkish birds of the same sex.
If the eastern and western populations are considered to be separable subspecies, it is unclear which should be considered to be the nominate (first-named) form, since the first description of this species was based on a now-extinct population from Switzerland which is of unknown race.
The northern bald ibis is readily distinguished from its close relative, the southern bald ibis of Southern Africa, by the southern species' whitish face. The northern bald can also be confused with the similarly dark-plumaged glossy ibis, which overlaps its range, but it is larger and stockier than that species. In flight, when the bill and face colouration may not be visible, the bald ibis' less rounded wings and shorter neck give it a different profile from glossy ibis, and its relatively short legs mean that its feet do not project beyond the tail, unlike those of the glossy ibis.
Habitat and range.
Unlike many other ibises, which nest in trees and feed in wetlands, the northern bald ibis breeds on undisturbed cliff ledges, and forages for food in irregularly cultivated, grazed dry areas such as semi-arid steppes, and fallow fields. The close proximity of adequate steppe feeding areas to breeding cliffs is an important habitat requirement.
The northern bald ibis was once widespread across the Middle East, northern Africa, and southern and central Europe; fossil bones have been found at Solothurn dated to the Mesolithic and Neolithic Periods. It bred along the Danube and Rhone Rivers, and in the mountains of Spain, Italy, Germany, Austria and Switzerland (Gesner's original description was of a Swiss bird), and most probably also in the Upper Adriatic region. It used castle battlements as well as cliff ledges for nesting before vanishing from Europe at least three centuries ago. It is also extinct over most of its former range, and now almost the entirety of the wild breeding population of just over 500 birds is in Morocco, at Souss-Massa National Park, where there are three documented colonies, and near the mouth of the Oued Tamri (north of Agadir), where there is a single colony containing almost half the Moroccan breeding population. There is some movement of birds between these two sites.
Religious traditions helped this species to survive in one Turkish colony long after the species had disappeared from Europe, since it was believed that the ibis migrated each year to guide Hajj pilgrims to Mecca. The ibis was protected by its religious significance, and a festival was held annually to celebrate its return north. The Turkish ibis population was centred near the small town of Birecik in the southeast of the country, and during the first half of the 20th century, the Birecik colony maintained a relatively stable population of about 500 breeding pairs, reaching an estimated total population of about 3,000 around 1930. By the 1970s, numbers had drastically declined and a captive breeding program was initiated in 1977 with one adult pair and nine chicks taken from the wild. This program largely failed to revert the decline; there were 400 birds in 1982, five pairs in 1986, and seven pairs in 1987. Only three birds returned from their wintering grounds in 1989, and just one in 1990. The returning birds died before they could reproduce, thus rendering the species extinct in the wild in Turkey as of 1992. Once the wild Turkish population became non-viable, the colony was maintained as a flock which was free-flying for most of the year but caged in autumn to prevent migration.
After the demise of the migratory Turkish colony, the northern bald ibis was known to survive in the wild only at the Moroccan sites, although occasional sightings of birds in Yemen, Eritrea, Saudi Arabia, and Israel during the 1980s and 1990s suggested that there was still a colony somewhere in the Middle East. Intensive field surveys in spring 2002, based on the knowledge of Bedouin nomads and local hunters, revealed that the species had never become completely extinct on the Syrian desert steppes. Following systematic searches, 15 old nesting sites were found, one, near Palmyra, was still hosting an active breeding colony of seven individuals. Although the ibis had been declared extinct in Syria more than 70 years earlier, the bird appears to have been relatively common in the desert areas until 20 years ago, when a combination of overexploitation of its range lands and increasing hunting pressures initiated a dramatic decline.
The Moroccan breeding birds are resident, dispersing along the coast after the nesting season. It has been suggested that coastal fog provides extra moisture for this population, and enables the ibises to remain year-round. In the rest of its former range, away from the Moroccan coastal locations, the northern bald ibis migrated south for the winter, and formerly occurred as a vagrant to Spain, Iraq, Egypt, the Azores, and Cape Verde.
Satellite tagging of 13 Syrian birds in 2006 showed that the three adults in the group, plus a fourth untagged adult, wintered together from February to July in the highlands of Ethiopia, where the species had not been recorded for nearly 30 years. They travelled south on the eastern side of the Red Sea via Saudi Arabia and Yemen, and returned north through Sudan and Eritrea.
Behaviour.
Breeding.
The northern bald ibis breeds in loosely spaced colonies, nesting on cliff ledges or amongst boulders on steep slopes, usually on the coast or near a river. Volunteer climbers have created extra ledge spaces in the Souss-Massa colonies to ensure that breeding population is not limited by the availability of nest ledges, and artificial nest boxes are used in the managed colony at Birecik. In the past, the birds also nested in buildings.
This ibis starts breeding at three to five years of age, and pairs for life. The male chooses a nest site, cleans it, and then advertises for a female by waving his crest and giving low rumbling calls. Once the birds have paired, the bond is reinforced through bowing displays and mutual preening. The nest is a loose construction of twigs lined with grass or straw. "G. eremita" normally lays two to four rough-surfaced eggs, which weigh an average of , and are initially blue-white with brown spots, becoming brown during incubation. An egg in the collection of the British Museum was marked more thickly at the broad end, with "spots and very small blotches of yellowish brown and pale rufous". It was 0.93 in long and 0.68 in wide (2.37 × 1.73 cm). The clutch is incubated for 24–25 days to hatching, the chicks fledge in another 40–50 days, and the first flight takes place at about two months. Both parents incubate and feed the chicks.
The northern bald ibis lives for an average of 20 to 25 years in captivity (oldest recorded male 37 years, oldest recorded female 30 years). The average age in the wild has been estimated as 10 to 15 years.
Feeding.
This gregarious species commutes in flocks from the cliff breeding sites or winter roosts to its feeding areas, flying in a V formation. The flocks may contain up to 100 birds in winter. During the breeding season, the ibises regularly forage up to from the colony, and, although steppe not in current cultivation is preferred for feeding, they will also use fallow ground, and occasionally even actively cultivated fields.
The northern bald ibis consumes a very wide variety of mainly animal food; faecal analysis of the