A flock of Asian Openbill stood on the sprawling marsh of Clevedon, a tea estate we were crisscrossing in search of rare birds. Being the most abundant stork of Bangladesh, the openbill is not a prized species to the bird-watchers, but we are always pleased to see this great survivor and an enigmatic creature in so many ways.
The wary flock of openbill took to the air as we trod too close to their comfort. Some of their black feathers displayed spectacular blue shades in the afternoon sun and the oddly shaped bills looked like a series of stroppy scissors ready to cut through the blue fabrics of the sky.
The openbill presented us with another weird aspect of their strange bill as they flew overhead. The bills are pretty thin when seen from below, although in profile those appear very broad and massive. Mercifully, the openbill does not carry as bulky bills as it seems from the side-view. While the bills have great depth, they are not wide at all.
That odd design of the openbill's bill was what fascinated the celebrated scientist, Sir Julian Huxley. He studied the openbill for a while and had a go at explaining the purpose of the perennial gap between its upper and lower beaks. That peculiar opening gave the bird its unusual English name 'openbill' and scientific name Anastomus oscitans, meaning 'yawning mouth'.
Interestingly in 1960, an East Pakistani zoologist was studying the birds at Oxford University, Sir Huxley's alma mater. Huxley promptly visited the students' dorm to gather information from him about the way openbills use their bills to crack open the molluscs. That student was our distinguished naturalist Kazi Zaker Husain.
However, Huxley speculated wrongly that the openbill cracks a snail by placing it in the gap between its bills just like a mechanical nutcracker. Later it was known that the openbill did no such thing. To be fair to the eminent scientist, we may mention that he studied some published pieces of literature and examined the dead birds only but did not get an opportunity to observe living openbills in the field.
Even in the field, the openbill baffled the biologists for a long time because the clever bird did the entire operation of opening up molluscs underwater. The bird need not see a snail in order to crack it. The famed nineteenth-century biologist Dr TC Jerdon found that even a blindfolded bird could forage in water and open up molluscs. Jerdon, however, did not speculate how the bird used its bills to do that.
The openbill forages in shallow water by repeatedly jabbing in the mud keeping its bill-tips slightly apart. When a bill touches a snail the tip is inserted in the shell's opening and the meat is extracted by shaking it from side to side. Then the bird lifts its bills up to swallow the meat, and the empty shell stays in the mud.
The trick that works so well on snails does not do so on the mussels. The openbill, therefore, brings the mussels out of the water and keeps those on the ground to die of exposure. The dead mussels open up spontaneously; then the openbills feast on it. If you see a pile of empty mussels at a marshland, you have narrowly missed an openbill luncheon.
The openbills, possibly, have benefited greatly from the growing cultivation of irrigated IRRI paddy in Bangladesh. When the country's rice production grew more than three-fold in 50 years, openbills thrived on the molluscs of the irrigated fields around the year.
Asian Openbill is the only large bird of Bangladesh the population of which has been growing steadily. It is also the only stock we see in Dhaka and in the paddy fields besides most wetland habitats of the country. The population of our other five species of storks, however, is so low that people barely know that they exist.
The Asian Openbill did not always have it so good. The use of DDT [an insecticide used in agriculture] took a huge toll on them in the latter half of the 20th century. The DDT is concentrated in the molluscs because they feed on the contaminated planktons in our inland water. The openbill used to consume those poisoned molluscs and perished silently. They have been recovering from that silent march of death only recently.
A similar process of molluscs poisoning is still going on for the African Openbill because DDT remained in use much longer in Africa in the name of malaria control. Studies find a very high concentration of DDT in the eggs of the African Openbill even today.
The African Openbill has to live with another issue no less pernicious than DDT. And that is the popular practice of eating 'wild meat' among many African people. These days the big game hunting is too demanding, and the birds have to supply much of their wild meat. And the storks being meaty birds bearing that brunt.
The Asian openbill has fared better than its African cousin on many counts. It lives only in Bangladesh, Cambodia, India, Laos, Nepal, Myanmar, Sri Lanka, Thailand and Vietnam where people irrigate their paddy fields copiously, keeping DDT at bay and caring little for the wild meat.
In Bangladesh, the openbill has benefitted additionally from a recent reduction in the number of large eagles that used to prey upon the openbill nestlings. The only remaining eagle that can rob an openbill nest is the White-bellied Sea Eagle living at the coast.
No wonder, the openbills of Bangladesh do not nest anywhere near the coast. They prefer to nest in a large colony on big trees at a burial ground or a holy site of some kind. Is that why their clamorous nestlings suddenly grow silent, sombre and focused as they leave the nesting site!