Colours of Wildlife: African Openbilled Stork

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African Openbilled Stork

Willem is a wildlife artist based in South Africa. He says "My aim is simply to express the beauty and wonder that is in Nature, and to heighten people's appreciation of plants, animals and the wilderness. Not everything I paint is African! Though I've never been there, I'm also fascinated by Asia and I've done paintings of Asian rhinos and birds as well. I may in future do some of European, Australian and American species too. I'm fascinated by wild things from all over the world! I mainly paint in watercolours. . . but actually many media including 'digital' paintings with the computer!"

Openbilled Stork by Willem

The birdie I bring to you today, has a special place in my heart. The African Openbilled Stork, Anastomus lamelligerus, was a favourite of my father's. Book illustrations show this species as being mostly dull and dark, and that's what it looks like, as well, when seen from a distance. But in 1985 my father got us some good binoculars for a trip to the Kruger National Park, and then for the first time we could get a truly good look at this species. My father was amazed to see the lovely bronze iridescence in the wing and breast feathers of this stork! We were lucky; the storks get the glossy feathers only during the breeding season, and they need to be seen in good light to be fully appreciated, but our stork fulfilled both those conditions. Ever since then my father has been a major fan of the openbill.

This is called an 'African' openbilled stork to distinguish it from the other kind, the Asian openbill. That species occurs over much of tropical Asia and is somewhat different-looking: it is mostly a dull, ashy grey, but becomes a brighter white colour with contrasting black wing and tail feathers, and reddish bill and legs, in the breeding season. African openbills occur throughout most of tropical sub-Saharan Africa, and also in western Madagascar. They're always associated with water, most frequently seen wading in the shallows of large, slow-flowing rivers, and also in swamps such as the vast Okavango of Botswana.

So what is the deal with those bills? The openbill has a conspicuous gap in its bill, even when it is fully closed, that stretches from about the middle of the bill to the tip. This opening is actually not the important thing; the angle at which the tips of the upper and lower bill meet, is. The bill tips meet in a pincer-like configuration which allows precision pinching. Openbills are specialized feeders, most of the time eating freshwater snails and mussels. The fine grasp of the bill tip helps them to pull these poor molluscs from their shells. Most of this is done underwater, so we don't know the precise mechanics, only that the openbills are quite expert at it. The gap in the bill only develops in adult birds; chicks and juveniles have ordinary straight, fully-closed stork-like bills. It takes a few years of adulthood before the bill configuration is complete.

The African openbill is also characterized by fine ridges called lamellae fringing the roof of the upper bill; I can't find any information about what that is for. It might have something to do with the bill's very keen sense of touch, helping the stork rapidly detect edible critters as it pokes about the mud. In addition to snails and mussels, openbills also eat the occasional crab, worm, fish, frog or aquatic insect.

In South Africa, openbills are seen mostly in the warm tropical and subtropical eastern and northern regions. The species is rather rare here. Further up north, it becomes much more common, often gathering in large flocks. Openbills typically patrol shallow water close to the riverbanks, but also sometimes perch on the backs of wading hippos. The occasionally feed at night. In days of yore, they occurred in very large numbers on the banks of the Zambezi, the big river that forms the northern boundary of Zimbabwe. So many nests were in the colonies that their eggs used to be a major food supply for migrant labourers traveling between northern countries and the South African gold mines. This may have depleted some of those colonies, but the storks founded many new ones. They are very opportunistic and move around the continent in response to heavy rainfall and drought. When rivers overflow their banks, a lot of new shallow-water habitat results, but sometimes drought also aids the birds when the receding waters expose beds of mussels.

Openbilled storks breed in large colonies, sometimes numbering a thousand adult birds. They prefer nesting in trees, choosing trees on islands surrounded by water, or shoreline trees that have become flooded due to rising waters. This gives them some protection from predators. If trees are not available, they will nest in reed beds. Often they nest alongside other wetland birds like ibises, cormorants, darters, herons and spoonbills. Couples display to each other in the breeding season: they bob their heads, clatter with their bills, and rock back and forward with their heads between their legs! Both sexes work at the breeding effort. The nests are made of sticks with a central depression lined with wet weeds collected from the bottom of pools. In this, the female stork lays three to four eggs. With her mate, she keeps the nest moist and cool by either adding more wet weeds, or regurgitating water onto the nest. When the chicks hatch, they sometimes get the regurgitated water treatment as well to keep them cool in the sweltering African sun. The chicks are raised exclusively on snails and clams.

This is not a threatened species. It occurs very widely and in considerable numbers in several regions. It may actually be Africa's most common stork species. Its main threats are pesticides and loss of habitat due to destruction or disturbance of wetlands by humans.

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