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!"

Here you have a family of ostriches! The ostrich, Struthio camelus, is the largest bird not only in South Africa but in the whole world. 'Struthio' is Latin for ostrich, while 'camelus' means as you might guess 'camel', here alluding to these birds often being found in dry regions. Here in South Africa, they are quite easy to see, being present in most large nature reserves and game parks, and also being farmed in a few regions, most notably the town of Oudtshoorn in the semi-desert Klein Karoo region. They are remarkable birds, in many ways good reminders that birds are indeed the living descendants of the dinosaurs.

Biggest of All

A male ostrich can reach a head height of 2.8 m/9' and a bodyweight of 155 kg/340 lbs. Their closest rivals in size are the cassowaries and emus of the Australian region, which only reach about 1.8 m/6' in height and rarely exceed 40 kg/90 lbs in bodyweight. Female ostriches are slightly smaller than the males. While the male is boldly black and white in plumage, the female is a dull greyish brown. The bare neck and legs of the male can vary in colour from bluish grey to pinkish. The front of the lower leg is protected by a row of tough scales that are often bright red in the male, especially in the breeding season, but blackish in the female.

Ostriches, though unable to fly, have large wings, with a span of 2m/around 7'. These are used for display, particularly the bobbing and weaving dance the male performs to charm the females in the breeding season. But ostrich wings also have an important link to the ostrich's body temperature. Like all large mammals living on the hot African savannah, ostriches can be in danger of overheating. The wings, covered in feathers on the outside, have large areas bare of feathers on the inside. An ostrich that is becoming too hot, can spread his wings away from his body. This allows air to circulate over the bare areas on the inner wing as well as over the bare upper thighs and large bare patches on the ostrich's flanks. This air circulation helps cool the skin and the network of blood vessels present in those patches. But when it is cool outside, the ostrich folds its wings close to its body, the outer covering of feathers then keeping its body warm.

An interesting feature of ostrich wings is that they have claws. The wings of birds are derived from the forelimbs, or arms, of the dinosaurs they evolved from. Inside the wing of a bird are the bones of the arms as well as the hands and fingers. In most birds, the fingers have fused together and lost the claws, and only support the feathers. In ostriches and a few other birds, if the feathers are removed from the wings, they still have a vaguely arm-and-hand-like appearance, and in the case of the ostrich, curved claws at the tips of the two remaining 'fingers'. This is not necessarily an indication of primitiveness; there are even some advanced flying birds such as the Hoatzin of South America, which in the chicks have clawed hands and fingers.

The legs of the ostrich are very large and powerful. Most of the muscle mass of the leg is concentrated in the upper thigh. Power and speed is transmitted from here to the lower leg and feet by the tendons and long leg bones. The ostrich foot is unique in the bird world for having only two toes. These are short and strong, the inner toe having a large, curved claw but the outer toe only a round stub or no nail at all. The curved claw is used as a weapon. A single kick from an ostrich can disembowel a lion … or a human! But ostriches will prefer running away from a fight. They can reach speeds of 70 km per hour/45 mph. They have great endurance and can keep up a trot for long distances.

Another superlative of the ostrich is its eyes! Reaching 50 cm/2" in diameter, the ostrich eye is the largest of any land-living animal. (They're greatly exceeded by the eyes of some oceanic creatures though, most notably giant squid.) With their long necks and huge eyes, ostriches can spot predators from far across the open savannah. Not that many predators would be willing to take on an adult ostrich! But lions and leopards sometimes catch them by ambush, while cheetahs have been known to run down and catch adult ostriches.

Superlative Breeders

Also when it comes to reproduction, ostriches are unique and excellent. As you might expect, they have the largest eggs of any bird species. These reach 15 cm/6" in length and 1.4 kg/3 lbs in weight. They are equal to about twenty chicken eggs. But the ostrich also holds the record for having the smallest eggs of any bird – relative to its body weight! The real limit to the size of a bird's egg is its shell. The shell must be thick enough to protect the egg from breaking during normal activity of the brooding parents, but not so thick that the little chick can't break it when it's time to hatch. An ostrich egg is still well within these limits. An adult human can stand on top of an ostrich egg without breaking it!

Another weird feature of ostriches are that they nest communally. They don't build huge nests like the Sociable Weavers their nests just being hollows scraped out in bare soil. But one ostrich male will court several females, giving the above-mentioned neck-and-wing dance. He also proclaims his territory by loud booming calls some people confuse with a lion's roar. The females who accept him and mate with him will all lay their eggs in the same nest scrape. The nest can end up with as many as sixty eggs, though fifteen to twenty is typical. The male and the females brood the eggs, the male usually taking the night shift. Here again the big wings of the ostrich come in handy, helping it to cover all the eggs. But it happens that many eggs on the margins are not adequately covered; eggs may also roll away from the nest, and the dominant female will even sometimes push some of the eggs of her rivals out of the nest. (Ostrich females can recognize their own eggs in the clutch!) This has the result that typically many of the eggs in an ostrich clutch fail to hatch.

Ostrich eggs are sought out by a great many predators. Eggs that have rolled well away from the main clutch are easiest to snatch. Some mongooses have learnt a trick of breaking an ostrich egg: they throw a heavy stone at it. Egyptian vultures (which actually occur much more widely than just Egypt, being found over most of Africa, and parts of Europe and Asia) have a similar trick, taking a stone in their bills and then smashing the egg with it. If you consider the size of an ostrich egg compared to that of a chicken, you can appreciate just what a store of nutrition it is.

As with the eggs, ostrich chicks are also very vulnerable, despite the protection of their powerful parents. Newborn chicks have a rather spiky-looking covering of coarse fluff, with striped heads and necks. They are born with open eyes and the ability to walk and run. They leave the nest immediately and accompany their parents. The male teaches them what is good to eat and how to find it. Ostriches consume almost anything they can gulp down, and are notorious for swallowing things not actually edible. They do eat rocks with a purpose, these helping grind up the other things in their bellies. They eat plants including lots of succulents which provide them with water in dry regions, and will catch invertebrates and other small animals. Ostrich chicks of different broods and ages often join each other to form large 'crèches'. This gives them some protection, but still many chicks get snatched by predators. Once they reach adulthood, however, their life expectancy rises dramatically. Adult ostriches have been known to live for more than sixty years.

Ostrich Relatives

Apart from ostriches, there are three main kinds of large, flightless birds surviving. The emus and cassowaries I already mentioned; then in South America, birds very similar to ostriches, though smaller, occur, called the rheas. There are two species. All of these birds are fairly closely related and share some anatomical features, such as lacking the keel on the breastbone that all other birds possess. This keel helps anchor the muscles they use for flying. Ostriches and other flightless birds have no need for this. The bizarre Kiwis of New Zealand are also related, being flightless and lacking a keel even though they are much smaller.

In the past, several other large flightless birds existed. Most noteworthy are the moas of New Zealand, and the elephant birds of Madagascar. Moas were the tallest of all birds, some exceeding 3 m/10' in standing height. The elephant birds of Madagascar were not as tall, but much heavier in build, and were among the heaviest true birds that ever existed, reaching perhaps as much as 500 kg/1100 lbs in weight. They also had the largest eggs ever, these reaching 33 cm/13" in length with a liquid volume of 4.5 l/2 gallons.

The distribution of these flightless birds presents a problem to biologists. They are all ostensibly related to each other, they cannot fly, and yet they are found in South America, Africa, Australia and New Zealand. These regions are separated from each other by large expanses of ocean; how did these flightless birds get there?

It has been known for some time now that the continents of the Earth haven't always been where they are today. A slow but inexorable process is pushing them around. This is called continental drift, and is accepted and well-understood today. It is known that some time ago, continents that are far apart today, actually were joined together. There was even a time, two hundred and fifty million years or so ago, when all the continents were joined in a single landmass called Pangaea. Back then, flightless creatures could have walked from any place in the world to any other place. But is this an explanation for the flightless birds and their distribution? The problem is, birds evolved long after Pangaea started to break up. The oldest creature considered a true bird (although that is a matter of semantics), Archaeopteryx, lived about 150 million years ago. But the ostrich and its other flightless relatives are much more advanced than Archaeopteryx, and hence must have evolved from a much more recent ancestor. It is difficult to see how they could have originated more than 80-90 million years ago, if even that much. By that time, the continents had already broken apart so much that the different groups of flightless birds wouldn't have been able to reach the places where they live today without needing to cross large stretches of ocean.

There is a surprising clue to this problem. While ostriches, emus, cassowaries, rheas and kiwis are all obviously related, and similar in being keel-less and flightless, another group of relatives of theirs have turned up. These are the tinamous of South and Central America. They are birds not at all ostrich-like, instead being very similar to partridges. For long they've been considered a group on their own. But recent studies confirm that they are actually related to the ostriches and other large flightless birds. Yet, tinamous can fly! Several fossils of tinamou-like birds have turned up, showing simultaneous relationship to these as well as to the ostriches and the others. These old ostrich-ancestors could fly! Therefore what is most likely the case, is that the ancestors of these large flightless birds were able to disperse over the world by flying, and then became flightless later. Why they all became flightless in these various different places, leaving only the tinamous still able to fly, is a different puzzle.

Ostriches proper also used to occur more widely. Today, in the wild, they are restricted to sub-Saharan Africa. Not long ago they used to occur in the middle East, being found in such places as Israel and Syria. There also used to be a species of ostrich that occurred in central Asia, even as far as China! Prehistoric ostriches also lived in Europa. Today, though confined to Africa, ostriches are still numerous and not in danger of extinction.

Ostriches and Humans

Ostriches are popular birds in various ways. They have long been hunted in Africa by people like the San/Bushmen, being sources of tasty meat. The San also use their eggs, these being excellent as containers for water. Ostriches are farmed today for their meat and leather as well as for their feathers, these being used for a variety of feminine fashions as well as for feather dusters. There is also the sport of ostrich riding! A big ostrich can support a small human jockey, and in South Africa ostrich races take place, the ostriches having special saddles and bridles. Ostriches are also used for pulling carts.

Then of course ostriches are regularly portrayed in the media. Their unique and odd appearance makes them good candidates for animated cartoons and movies, as well as advertisements. Ostriches are especially famous for the claim that, when perceiving a predator, they hide their heads in the sand, thinking that if their head is concealed, so is their whole body. This is of course hogwash, as I've made clear earlier: ostriches are very alert and will run or fight if threatened. However they will, when they suspect that the predator has not spotted them, though they have spotted it, try to hide, by lying flat on the ground. They certainly don't lower their head alone, but their entire bodies, trying to be as flat as possible and making use of shrubs and trees for concealment. But the idea of an ostrich hiding its head in the sand has become so iconic that it doesn't matter anymore what real ostriches do!

Colours of Wildlife Archive

Willem

09.03.15 Front Page

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