African Openbill

识别特征

The African openbill is a stork measuring 80–94 cm (31–37 in) and weighing 1–1.3 kg (2.2–2.9 lb). The species does not exhibit any major sexual dimorphism, although the males are slightly larger than the females and have a longer and heavier bill. The adult bill is between 135–196 mm (5.3–7.7 in) in length, brownish in color and has a gap between the upper and lower mandible. This gap is non-existent in juvenile birds and develops as the bird ages. It is because the two mandibles of the beak only meet at the tip and not in the middle that this stork genus received the name of “openbill”.<p>The adult plumage is overall black with iridescent green feathers on their backs, coverts and abdomens. The juvenile plumage is usually less vibrant and browner in color with the feathers of the underparts having pale tips. The legs and feet are black. The eyes are grey with grey lores and no distinct coloration of the eye-ring.<p>The gap in the bill of the African openbill was first hypothesized to serve as a nutcracker, crushing the shells of the snails this stork feeds on. Scientists later demonstrated that the bill does not serve this function. Rather the opening between the two mandibles facilitates grasping the shells of the snails. The convergent tips of the mandibles prevent the slipping forward of a spherical object being carried by the storks. The curve in the lower mandible allows the stork to have the perfect angle of attack to force its way under the operculum and release the molluscs from their shells. The bill of the African openbill storks closely evolved with the bird’s specialized diet, allowing for the perfect handling of snails and other molluscs.<p>Many of the social displays of the African openbill stork are accompanied by bill clatters as is common in most of the Ciconiidae species. This bird also croaks and honks loudly.<p>These storks are smaller in stature than most of the other species in their family, which allows them to be much more agile in the air. This agility can be observed during their descents from high altitudes as they often perform steep dives and remarkable acrobatic manoeuvres. During their migration flights, the African openbill storks will use sustained flapping flight with an average wing flap rate of 200–210 flaps/minute. They will also often soar on the thermals when commuting to and from distant feeding areas. This allows them to travel long distances to obtain food without expending too much energy. In flight, these birds have their necks and head extended and their long, broad wings are spread out and perfect for soaring and gliding on the air currents.<p>The adult African openbill does not have many predators, although the species is preyed upon by the tawny eagle (Aquila rapax). The eggs of the African openbill are preyed on by the African harrier-hawk (Polyboroides typus), the African marsh-harrier (Circus ranivorus) and monitor lizards (genus Varanus).<p>Adult African openbills have dark shiny feathers on their wings and chest that serve in parade and other types of signaling between individuals of the species. These special feathers do not follow the typical structure of feathers. Usually, feathers have a rachis, barbs and barbules, but none of that is found in these parade feathers. Instead, the feathers have a single ribbon-shaped body and a few long, fine stems that disperse laterally from the flat part of the ribbon. This structure serves to create the iridescent colors observed on the feathers. The bottom part of the feathers presents the normal structure of feathers and serves for insulation purposes. It does not produce any color. <p>The coloration is perceived on the outside of the ribbon structure and therefore the iridescence is produced by the external portion of the cortex. This cortex consists of melanin nodules repeated periodically along planes inside the ribbon. These planes are parallel to each other. Scientists believe the dark green appearance of these feathers to be due to the low reflectance levels of the melanin nodules. <p>Two color-producing processes have been proposed to explain why these feathers have a green coloration: <p>The African openbill stork is considered out of danger worldwide as it is abundant in various portions of its range. There are no current estimate for the total population numbers, but they appear to be quite stable. Although they are not currently threatened, they remain a large bird with low reproductive success meaning that human activities affecting their habitat could have a big impact on the species.

分类信息

Genus: Anastomus; Family: Ciconiidae; Order: Ciconiiformes.

学名

Anastomus lamelligerus

命名信息

Temminck, 1823

目

Ciconiiformes

科

Ciconiidae

属

Anastomus

分布与栖息地

African openbill storks live in every habitat where suitable mollusc prey can be found. Their preferred habitats remain long stretches of freshwater. They can sometimes be seen far from humid habitats, but only exceptionally. The place you are most likely to see them are on large freshwater wetlands with nearby tall trees or shrubs for them to nest in. <p>Some African openbill population are trans-equatorial migrants. Timing their migration to arrive in West Africa for the start of the dry period. They migrate in flocks and most of the reason and organisation behind these movements remain unknown. Some populations migrate while others are residents, migration in African openbill highly depends on the weather conditions.

迁徙

Complete migrants

行为

Migration pattern: Complete migrants.

保护状况

Population trend: stable.

种群趋势

stable