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!"

The African Black Oystercatcher, Haematopus moquini, is a sturdy shorebird with a stout and powerful bill that it uses expertly to capture and ingest its mollusc prey. In overall length, it reaches 40-45 cm/16"-18" with a bill measuring up to 9 cm/3.5". Unusually for birds, the females are slightly larger than the males. It is a fairly rare species, with about 6 000 adult birds estimated to exist. It lives all around the shoreline of South Africa and Namibia, rarely straying further north to Angola and Mozambique. No other shorebird looks like it. It often betrays its presence by its resounding 'klee-eep … klee-eep' calls as it flies low over the beach. The scientific name means 'Moquin's blood-foot' and commemorates its discoverer, Alfred Moquin-Tandon, as well as referring to the red legs and feet.

A Bill the Bane of Bivalves

Bivalves are the molluscs that have a pair of shells fitting tightly together, like oysters and mussels. The oystercatcher deftly deals with these. It pries a mussel out of its bed, turns it over, and pecks a hole in the softer bottom of the shell. Then it inserts its bill in the hole, and bites the adductor muscle in half, the one that the mussel uses to keep its shells tightly closed. Then it is easy to peck out and swallow the soft body of the mollusc. At other times, the oystercatcher will insert its bill into the gap between the shells, if the mollusc opens up, and sever the muscle in the same way. It also chisels limpets off the rocks on which they fasten themselves, or hammers directly through their shells to get at the flesh.

Apart from molluscs, oystercatchers will also feed on other small critters of the shores: worms, crustaceans, insects, and even fish if they can catch them.

In the closely related Eurasian Oystercatcher, feeding behaviour has been found to significantly change the outward form of the bird's bill. Some oystercatchers actually don't feed on oysters much, instead probing into the beach sand for worms and other digging critters. These oystercatchers have finely pointed bills, which afford a delicate grasp. Those oystercatchers that feed more on molluscs and other bivalves, have broader-tipped beaks that are more powerful chiselling tools. It is the foraging strategy in itself that causes the change in the beak. The horny material of which the beak is made, called keratin, the same as fingernails, grows very rapidly, and the wear and tear on it fashions it into shape. Birds usually learn a specific foraging strategy from their parents, and it stays in the family, but individual birds can actually adopt a new method and in response their bills will change.

That's for the Eurasian oystercatcher; it's not yet known if something similar goes on with the African species. The two species co-occur in South Africa sometimes. The Eurasian oystercatcher is a rare visitor to our southern shores. It can easily be told from the African because it has a white belly and white wing and tail feathers. It also prefers subtly different coastal areas. While African oystercatchers mostly roam the rocky places, the Eurasian birds prefer sandy or muddy parts.

In South Africa, black oystercatchers live and breed mainly in the south and southwest. Like other seabirds, they make use of small off-shore islands for breeding and feeding, since they're safer there from predators and disturbance. It is the limited presence of these islands that chiefly constrains the numbers of breeding oystercatchers in South Africa.

The breeding season for oystercatchers goes from October to March, which in the southern hemisphere is spring to early autumn, but is mainly in the summer. Oystercatchers are monogamous; there is not much display between the mated birds, but they chase each other, sometimes with a butterfly-like fluttering flight. They nest in sandy or pebbly places. A pair will stick to the same nest year after year. The nest is just a small hollow scraped out with the feet. Often, black oystercatchers situate these nests close to tangles of dried-out, black seaweed, so that the bird sitting on the nest is hidden or camouflaged. Normally the female lays two eggs, but sometimes one or three. The spotted eggs look just like beach pebbles. Male and female both incubate. In the often sweltering summer heat, it's more important to keep the eggs cool than keeping them warm, and on hot days, instead of sitting on the eggs, the female will stand with her body above them, shading them. Sometimes she will soak her belly feathers in the seawater prior to sitting on the eggs. She will distract people and predators away from the nest with noisy and injury-faking displays. The chicks emerge after 32 days or so. They have soft, dense down covering their bodies and hatch with open eyes; they soon are able to walk, and can also swim if necessary. If a chick fears danger, it crouches down among tangles of seaweed or other beach detritus, where its spotted down camouflages it well. It walks along the beach with its parents, but can't yet feed itself. They will extract the edible parts from shellfish for it. Only when it is adult and its bill is full-size, will it be able to open oysters, mussels, limpets and other shelled molluscs for itself.

Many chicks die, but oystercatchers that survive their youth can live for 35 years, breeding for 25 of those years. Oystercatchers face several threats. Sometimes a nest is washed away by a high spring tide; the eggs are sometimes eaten by Kelp Gulls or by mongooses. A natural risk is the occasional 'red tides' or algal blooms that release toxins in the water, poisoning the shellfish the birds feed on. Mostly the birds suffer from humans. South Africa's beaches are quite popular with people, and these disturb nesting birds, or trample their eggs. Some people think it's fun to drive along wild coastlines with their four-wheeled drive vehicles, and again many nests and eggs get crushed.

Fortunately, at present oystercatchers benefit from the protection of many of their nesting beaches, and communities are also more informed of their needs. There are projects afoot to ring birds and track their movements. The population, though small, is currently stable, and the African black oystercatcher is not considered endangered. Worldwide, on all continents except Antarctica, elven species of oystercatcher occur, and another one, that lived on the Canary Islands, recently became extinct. It was the closest relative of the African black oystercatcher.

Colours of Wildlife Archive

Willem

22.07.19 Front Page

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