Anastomus – Openbills

Anastomus is unique within the stork family, consisting of two species known as openbill storks: the Asian openbill (Anastomus oscitans) found in Southern Asia and the African openbill (Anastomus lamelligerus) located in tropical Africa and Madagascar. The “openbill” descriptor is derived from the notable gap (or “anastomosis”) present between the mandibles of their bills, a trait that is most apparent when the bill is closed and which facilitates their specialized feeding habits.

The morphology of the openbill storks is specifically adapted for their preferred diet of mollusks, particularly snails. The shape of their bill allows them to deftly handle and extract snails from their shells—a skill that sets them apart from other stork species. Openbills have been observed using their bills to probe into the water and mud with surgical precision, easily grasping and manipulating their slippery prey.

Openbill storks favor freshwater wetlands as their habitat, including marshes, rivers, ponds, and canals. They are also commonly found foraging in flooded agricultural areas such as rice paddies, which are rich in their preferred food sources. Their presence in such areas is a testament to their adaptability and their important ecological role in controlling snail populations, which can be agricultural pests.

Socially, openbill storks are highly gregarious birds. They form large nesting colonies, often in trees near water bodies, where they engage in complex social interactions. These colonies can become quite sizable, with numerous nests crowded into a single tree. The African openbill, in particular, is known for its opportunistic nesting behavior, which is closely linked to the availability of its snail prey. In seasons where snails are abundant, these storks may breed more prolifically.

Breeding among openbill storks is mostly seasonal and can be influenced by rainfall patterns, which affect the availability of their prey. During the breeding season, these storks engage in courtship displays that include bill-clattering and mutual preening to strengthen pair bonds.