The African Openbill (Anastomus lamelligerus ) is a species of stork from the family Ciconiidae. It is widely distributed in Sub-Saharan Africa and western regions of Madagascar. This species is considered common to locally abundant across its range, although it has a patchy distribution. Some experts consider there to be two sub-species, A. l. lamelligerus distributed on the main continent and A. l. madagascariensis living on the island of Madagascar. Scientists make the difference between the two sub-species due to the more pronounced longitudinal ridges on the bills of adult A. l. madagascariensis.The Asian Openbill (Anastomus oscitans ) distributed in Asia is the African Openbill’s closest relative. The two species share the same notably large bill of a peculiar shape that gives them their name.
The African Openbill is a stork measuring 80-94 cm and weighing 1-1.3 kg. 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 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”.
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.
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.
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.
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.
These birds primarily feed on aquatic snails of the genus Pila. They have been observed to also eat freshwater mussels. In different parts of their range, some individuals have been observed to eat terrestrial snails, frogs, crabs, fish, worms and large insects. It is important to note, that none of these are the preferred food choice of the African Openbill.
To forage for snails, the African Openbill stands in shallow water, repeatedly dipping its beak in. They hold their bill slightly ajar and will snap it shut if they encounter a prey. Once they have a hold on the prey, they hold it with the tip of their mandibles and carry it back to shore. The storks will start slowly walking around and changing location, if they do not capture anything in the area they decided to forage in.
The African Openbill sometimes forages by standing on the back of hippopotamuses (Hippopotamus amphibius ). As the hippopotamus wades through the vegetation, it upturns it and exposes the multiple snails that cling to the undersides of the plants. The stork will then feed on these exposed snails that have become easy prey. The hippopotamus does not seem to mind the presences of the bird on its back and is not harmed by it in any way.
Lastly, very few individuals have been observed to forage visually from afar. There are accounts of African Openbill storks swooping down from their nest and immediately securing a prey. This behavior is extremely uncommon for the stork but does occur.
African Openbill storks are opportunistic breeders. The species forms monogamous pairs and breeding colonies usually contain less than 60 pairs. These colonies can either be formed of only African Openbills or be mixed with cormorants, herons, African spoonbills, African daters and other storks. The breeding success of the African Openbill stork is estimated to be less than one young per pair per year.
The occurrence of the breeding season varies with distribution as the hatching of the nestling is timed to coincide with the emergence of snails. It can start either just before, at the beginning of or late in the rainy season. The bulk of the breeding season occurs during the rainy season and peaks in January-March. The rain season last from August to May.
African Openbill storks’ nest in tall trees and often favor the lowest branches of those trees. The nest which usually takes up to a week to build and both sexes contribute to the construction. The African Openbill builds a nest that is ~50 cm wide, which is relatively small for this medium sized bird. The nest consists of a thin platform of sticks and twigs, lined with leaves, grasses, sedges and other aquatic plants.
The female African Openbill will lay 3 to 4 eggs. These are oval and chalky white. Both parents will then care for the eggs through the incubation period of 25-30 days. When taking care of the eggs, the parents can occasionally be seen regurgitating water over them. The exact nature of this behaviour remains unknown, but scientists believe it serves to cool down the eggs. Once the chicks have hatched, parental care continues to be shared by both parents and both the male and female will bring food and care for the hatchlings. After 50-55 days in the nest, the chicks will fledge and leave the nest.
Habitat loss, disturbances of feeding areas, pollution from pesticide used on mosquitoes and entanglement in fishing lines all pose potential threats to these birds. The African Openbill does remain common in habitats suitable for them, but human activity could pose a danger to the species.
