Greater Adjutant

Identificazione

The greater adjutant is a huge bird, standing tall at 145–150 cm (4 ft 9 in – 4 ft 11 in). The average length is 136 cm (4 ft 6 in) and average wingspan is 250 cm (8 ft 2 in), it may rival its cousin the marabou stork (Leptoptilos crumeniferus) as the largest winged extant stork. While no weights have been published for wild birds, the greater adjutant is among the largest of living storks, with published measurements overlapping with those of the jabiru (Jabiru mycteria), saddle-billed stork (Ephippiorhynchus senegalensis) and marabou stork (Leptoptilos crumeniferus). Juvenile greater adjutant storks in captivity weighed from 8 to 11 kg (18 to 24 lb). A greater adjutant after recuperating in captivity from after injury during nest collapse was found to weigh 4.71 kg (10.4 lb) as a nestling and to weigh 8 kg (18 lb) after reaching maturity and ready for re-release. For comparison, the heaviest known wild stork was a marabou stork scaling 8.9 kg (20 lb), with adult marabou ranging from 4–6.8 kg (8.8–15.0 lb) (females) and 5.6–8.9 kg (12–20 lb) (males). The huge bill, which averages 32.2 cm (12.7 in) long, is wedge-like and is pale grey with a darker base. The wing chord averages 80.5 cm (31.7 in), the tail 31.8 cm (12.5 in) and the tarsus 32.4 cm (12.8 in) in length. With the exception of the tarsus length, the standard measurements of the greater adjutant are on average greater than that of other stork species. A white collar ruff at the base of its bare yellow to red-skinned neck gives it a vulture-like appearance. In the breeding season, the pouch and neck become bright orange and the upper thighs of the grey legs turn reddish. Adults have a dark wing that contrasts with light grey secondary coverts. The underside of the body is whitish and the sexes are indistinguishable in the field. Juveniles are a duller version of the adult. The pendant inflatable pouch connects to the air passages and is not connected to the digestive tract. The exact function is unknown, but it is not involved in food storage as was sometimes believed. This was established in 1825 by Dr. John Adam, a student of Professor Robert Jameson, who dissected a specimen and found the two-layered pouch filled mainly with air. The only possible confusable species in the region is the smaller lesser adjutant (Leptoptilos javanicus), which lacks a pouch, prefers wetland habitats, has a lighter grey skull cap, a straighter edge to the upper mandible, and lacks the contrast between the grey secondary coverts and the dark wings.<p>Like others storks, it lacks intrinsic muscles in the syrinx and produces sound mainly by bill-clattering, although low grunting, mooing or roaring sounds are made especially when nesting. The bill-clattering display is made with the bill raised high and differs from that of the closely related African marabou which holds the bill pointed downwards.

Tassonomia

The greater adjutant was described in 1785 by the English ornithologist John Latham as the "giant crane" in his book A General Synopsis of Birds. Lathan based his own description on that given by Edward Ives in his A Voyage from England to India that was published in 1773. Ives had shot a specimen near Calcutta. In his account Latham also mentioned that he had learned from the traveller Henry Smeathman that a similar species was found in Africa. When in 1789 the German naturalist Johann Friedrich Gmelin revised and expanded Carl Linnaeus's Systema Naturae, he included the greater adjutant, coined the binomial name Ardea dubia and cited Latham's work. Gmelin did not mention the coloured plate of the bird that Latham included in his 1787 Supplement to the General Synopsis of Birds. Latham based his plate on a drawing in the collection of Lady Impey that had been made of a live bird in India.<p>There was some confusion as to whether the African marabou stork represented a separate species. In 1790 Latham in his Index Ornithologicus repeated his earlier description of the Indian species but gave the location as Africa and coined the binomial name Ardea argala. Finally, in 1831 the French naturalist René Lesson described the differences between the two species and coined Circonia crumenisa for the marabou stork.<p>The greater adjutant is now placed with the lesser adjutant and the marabou stork in the genus Leptoptilos that was introduced in 1831 by the French naturalist René Lesson. The species is monotypic: no subspecies are recognised.<p>The marabou stork of Africa looks somewhat similar but their disjunct distribution ranges, differences in bill structure, plumage, and display behaviour support their treatment as separate species.<p>Most storks fly with their neck outstretched, but the three Leptoptilos species retract their neck in flight as herons do, possibly due to the heavy bill. When walking on the ground, it has a stiff marching gait from which the name "adjutant" is derived.

Nome scientifico

Leptoptilos dubius

Autorità

(Gmelin, JF, 1789)

Ordine

Ciconiformi

Famiglia

Ciconidi

Genere

Leptoptilos

Areale e habitat

This species was once a widespread winter visitor in the riverine plains of northern India. However, their breeding areas were largely unknown for a long time until a very large nesting colony was finally discovered in 1877 at Shwaygheen on the Sittaung River, Pegu, Burma. It was believed that the Indian birds bred there. This breeding colony, which also included spot-billed pelicans (Pelecanus philippensis), declined in size and entirely vanished by the 1930s. Subsequently, a nest site in Kaziranga was the only known breeding area until new sites were discovered in Assam, the Tonle Sap lake and in the Kulen Promtep Wildlife Sanctuary. In 1989, the breeding population in Assam was estimated at 115 birds, and between 1994 and 1996 the population in the Brahmaputra valley was considered to be about 600. A small colony with about 35 nests was discovered near Bhagalpur in 2006. The number increased to 75 nests in 2014. Fossil evidence suggests that the species possibly (since there were several other species in the genus that are now extinct) occurred in northern Vietnam around 6000 years ago.<p>During the non-breeding season, storks in the Indian region disperse widely, mainly in the Gangetic Plains. Sightings from the Deccan region are rare. Records of flocks from further south, near Mahabalipuram, have been questioned. In the 1800s, adjutant storks were extremely common within the city of Calcutta during the summer and rainy season. These aggregations along the Ghats of Calcutta, however, declined and vanished altogether by the early 1900s. Improved sanitation has been suggested as a cause of their decline. Birds were recorded in Bangladesh in the 1850s, breeding somewhere in the Sundarbans, but have not been recorded subsequently.

Migrazione

Specie stanziale

Comportamento

Comportamento migratorio: Specie stanziale.

Conservazione

Tendenza della popolazione: in aumento.

Tendenza della popolazione

in aumento