Called ratites, the flightless birds are a class by themselves. They show hoe the process of natural selection works. Although losing the ability to fly indicates a retrograde evolutionary step, there’s more to it than meets the eye.
Nature’s richest gift to the animal world of prehistoric days was the gift of flight to the reptiles which became birds. From the study of fossils, scientists have determined that birds descended from a group of ground-dwelling dinosaurs known as theropods. The hideous monsters that first began to fly were pterosaurs, i.e. winged reptiles.
(Picture, below). They had great toothed beaks and huge bat-like membrane wings supported chiefly by an enormous finger. Some had a wing-span of 7.5 metres (25 feet) which provided sufficient lift to enable pterosaurs to become airborne. Somehow they all perished, as did most of the other species of dinosaurs.
Only the theropods evolved into birds.
Thanks to the power of flight, birds now occupy and exploit a wider range of habitats than any other class of animals. As a result of their supreme mobility, birds are, numerically at least, most successful terrestrial vertebrates on our planet. There are some 8,900 living species of birds, compared with 3,000 amphibians, 6,000 reptiles and 4,100 mammals. Birds owe much of their dominance to their ability to fly. It is, 1herefore, something of a surprise that a few species of birds are flightless, while retaining all or most of the other characteristics of their avian relatives.
The flightless birds are known as ratites, from the Latin word for raft (ratis), referring to breastbones that are flat like a raft. Such earthbound birds are unequipped with a keel that can support 1light muscles. (See diagram). In birds capable of powerful sustained flight, as much as 35w to 40% of body weight may be devoted to flight muscles which provide energy for flapping wings. As the breastbone is the chief anchorage for these muscles, its size is a good index of a bird’s capacity to fly. At the first illustration in the diagram shows, ratites have only rudimentary keel, though their ancient relatives had the full version which made them great fliers. With the keel almost gone, things are different today.
Why did these birds give up flying? The question might usefully be answered by asking another question: why do birds fly at all, considering that active flight is a very energy-consuming activity?
There are many reasons, all of which boil down to just one objective: Survival. Winging away from earthbound predators has been / a major use of flying. Many birds such as nightjar and flycatcher,
pick up their food in the air. Most birds need to fly to their food which may be located in the top
branches of tall trees or far away from their nests. Many birds need to escape from seasonal hardships that the local environment imposes upon them—and that is why some birds regularly undertake migration every year, from one continent to another.
However, flying is an expensive mode of travel. For example, a 20 gram bird flying at only 35 kilometres per hour, expends about 60 calories per kilometre flown. At speed both faster and slower than 35, it consumes more energy. The energy lost must be replenished by searching more food, which might necessitate a few more flights, again at the expense of energy.
This underlines the point that in environment—as in economics—there is no such thing as free lunch. So, when the advantages of flight no longer compensate for its cost, a bird may abandon flight. The adage ‘use it or lose it’ is tightly intertwined with the process of evolution. Since the bird seldom or never uses its wings, they may atrophy and disappear over a period of time.
As a rule, flightlessness is associated with geographical isolation and the relative absence of predators. Especially oceanic islands have this kind of situation, where most species of flightless birds are found today. In fact, wings may be a handicap to island birds by increasing their chances of being caught up in gale-force winds and blown away into the sea. if the land base is nothing more than a small speck in the middle of the vast ocean, a flying bird is certainly at a great disadvantage. So why not give up flying altogether and stay on the ground which is fortunately free of predators? It is in such protective isolation that some birds have traded their wings for terrestrial life. And because they did not have to lift their bodies off the ground by flying, most have grown bigger than other birds.
Fossil studies by scientists indicate that various flightless birds have lived on Earth at different times. A few of the ratites, extinct as well as living, are particularly noteworthy for their prodigious size, unusual frame and behavioural pattern. Some of these far-out birds deserve to be short-listed for pictorial
introduction. Here’s the lineup:
About 2,000 years ago, travellers from south-east Asia landed on the shores of Madagascar. There they encountered the elephant bird, a flightless creature that weighed more than 450 kilograms.
In his travelogue, Marco Polo described a bird, native to an Indian Ocean island, which was so big that it fed on elephants. The elephants were killed by raising them aloft and smashing them onto the ground. Obviously, no bird could have managed to dispose off the largest terrestrial animal in this manner and Marco Polo was quite deservingly branded a liar. It was not until France claimed Madagascar in the 17th century and the French colonists began reporting tales of colossal birds’ eggs used by the native as water casks. The birds that laid the outsize eggs had already been wiped out by immigrant hunting men several hundred years ago. And no, they did not eat elephants, but gorged themselves on the grass. Yet the fable left its imprint and the extinct birds came to be known as elephant birds.
The elephant bird’s egg was so large that it measured 34 x 24 centimetres and could hold 8 litres of water. Shells of this egg were heavy and thick enough to be fashioned into eating bowls by the aborigines of Madagascar. At the other extreme is the tiny vervian hummingbird of Jamaica, whose egg is less than 10 millimetres long. One egg of the elephant bird could hold the contents of about 50,000 eggs of this small humming bird. In the dry southern districts of Madagascar, fragments of the elephant bird’s eggs are numerous, and occasionally an egg is found intact. Years ago, one such egg was unearthed by a native. It was unblemished, and looked as it it had been laid only a few days before, but was probably several hundred years old. It weighed 8 kilograms.
Until 1300s, New Zealand was home to 19 species of moa, another giant flightless bird. Although not quite as heavy as elephant birds, they would have overshadowed them with height of 3.65 metres. Like elephant birds, they lasted a few hundred years after the arrival of humans. New Zealand was a world apart for nearly 190 million years. After the first Polynesians set foot in New Zealand, they hunted moa indiscriminately, reducing most of them to piles of bones. It was chiefly from the subfossil remains that zoologists were able to piece together what moas must have looked like, There is evidence that a few of these birds were alive at the turn of the 16 century. Remains of some were so well preserved that the gizzard contents could be identified. Apart from berries seeds and grass, the gizzard also held upto 2.5 kilograms of stone, probably as millstones for grinding the seeds.
Moas were almost entirely herbivorous and amount eaten must have been considerable. As herbivores they had to eat a larger amount of food than a carnivore of corresponding bulk to obtain the same food value, Moas, like certain other flightless birds, were able to grow so successfully because of their isolation from significant competition or predators. It seems they evolved very rapidly in the favourable New Zealand environment.
large and plentiful moas were of course an important item of food for the local human population and the Polynesians who immigrated to New Zealand less then 1,000 thousand years ago developed a moa-hunting culture. 5ome natives of New Zealand, who visited England in the late 19th century, told stories of their forefathers having hunted the giant bird with spears. No one knows at what point of time these forest dwelling birds eventually died out, but when Captain James Cook visited New Zealand in 1769, there were no moas left.
Related to pigeon, the dodo was an inhabitant of Mauritius. The first Europeans to land on this island were the Portuguese, in 1507, and the name ‘dodo’ derived from the word ‘doudo’-a simpleton.
The dodo was a massive bird and was supported on short legs and feet. The plumage was grey and the tail was a soft tuft of curled feathers. The head was most unusual, being very large and carrying
a heavy, strongly hooked dark- coloured beak.
Like many other birds which had lived for long without any serious enemies and without human
interface, the dodo, when first discovered, were quite unafraid of man or his introduced animals. Thus they were easily killed.
Pigs, dogs and monkeys brought to Mauritius island by Portuguese sailors during the 16th century destroyed the eggs and ate the young. And the earthbound dodo could not lay eggs in places inaccessible to these animals. Having no particular enemies on the island, it had never developed methods of self defense.
By 1681, the dodo was extinct, and the saying ‘as dead as dodo’ has long been used to denote anything that is completely passé or extinguished. No authentic dodo skin exists, but heads and feet have been preserved, besides much skeletal material. with these rudimentary objects, good models of the
dodo have been made with feathers of
appropriate form and colour taken from their birds. However, we know very little of the life of these very unusual birds. Two related species lived on nearby Reunion and Rodrigues Islands.
There is one aspect of extinction that is overlooked by most people who are otherwise staunch advocates of conservation. When a species dies out, it is invariably followed by one or more species into oblivion. The natural world, after all, exists as a web of life in which interrelationship of species is common. The dodo’s extermination too has a grim offshoot. There is a tree in Mauritius whose seeds will not germinate unless the fruit has first passed through the digestive track of the dodo. The dodo’s digestive juices dissolve the tough outer layer of the seed. when it is deposited (with manure) it sprouts. With the dodo gone, new trees no longer grow and the existing trees will sooner or later be dead. Yes, as dead as dodo.
This is a large flightless bird living in the tropical rain- forests of New Guinea and adjacent islands and in Northern Australia. The feathers of the cassowary (picture, above) have a glossy sheen, but are coarse and hair-like, and the wing is reduced to a mere vestige. There four species of this bird, all have bare heads surmounted by a 15 centimetres high horny helmet, and the bare skin of the necks is brilliantly coloured. Some cassowaries stand as high as 1.5 metres (5 feet) weigh 80 kilograms, and are most impressive among all flightless birds. Upon the stumpy wings are five spiny quills, and the cassowary strikes with these when it fights. But its strong and three toed feet are its chief weapons.
Years ago, a gentleman was resting in the middle of the day near a forest in New Guinea, When a cassowary stalked forth, Two big bloodhounds which he had with him immediately attacked the bird, but it was not in the least afraid of the powerful brutes. It struck out left and right with its terrible feet, and soon stretched one of the hounds dead upon the ground. The other hound tore open the flesh of the cassowary’s breast, but the bird continued to fight, and would have killed that dog, too, had not the man at last succeeded in putting an end to the fight. Being a kind man, the traveller stitched up the wound of the cassowary, gave it a good meal, and let it go. It went quietly back to the forest as if none the worse for its battle.
This flightless New Zealand bird stands about 45 centimetres high and lacks a tail and visible wings. So strange a bird is the kiwi that many doubted its existence long after it was described in England by Dr. Shaw from a specimen obtained in 1813.
The common kiwi lives in both the North and South Islands, and there are two other species in the South Island. They differ from all other birds in having their nostrils near the tip of the beak; they have a keen sense of smell and feed by probing in the ground for worms. The wings cannot be seen outside the body.
Long hair protrude from the face and forehead which, together legs, give the bird a unique appearance—and a very comical one. They are birds of the damp New Zealand forests, feeding at night on worms, insects and berries.
They are rarely seen, not because of rarity, but rather because they are shy and can move nimbly through the forest at night. Those who can recognise the calls know that they are quite common in many forested areas and even in scrub and in grassland bordering on forest.
As a rule, the larger the bird, the smaller its egg is in relation to the parent’s size. The big ostrich lays an egg that weighs only 1.7% of its body weight. while the tiny hummingbird lays an egg that equals 13% of its body weight. The eggs of the large albatrosses equal about 6% of their body weight. Probably the species that holds the record for laying the relatively largest egg is the kiwi, a hen sized bird weighing about 1.8 kilograms. Its enormous egg weighs about 420 grams or about one fourth of the bird’s body weight.
The female’s sole task is to produce the enormous eggs (usually two), each about a quarter of its weight. The male incubates the eggs for about 7s days, and though the chicks can find their own food soon after hatching they stay with their father for a considerable time.
This strange nocturnal parrot (picture, above) found in the forests of New Zealand is unusual in the sense that, unlike other parrots, it has lost its power of flight. It may, therefore, be presumed that the kakapo has been isolated from other parrots for a considerable time. Its 60 centimetres long body has
stubby, rounded wings that are useless for flying, though they help the bird to cover a short distante by gliding. That is how the kakapo hops from a higher branch of a tree to a lower one.
The bird is often called ‘the owl parrot’ since it is active only by night and also because it plumage is as soft as that of an owl. However, it prefers only vegetable matter as its food, which includes berries, nectar and leaves of some plants. Leaves, which are fibrous, are not swallowed, but are chewed thoroughly to extract juice and the residual stuff is discarded as a ball.
The first settlers in New Zealand were the Polynesians, who later came to be known as Maoris. They hunted the giant moas to extinction, but the kakapo survived, possibly because it appeared from its abode only after sunset. Its population was still widespread when the European setters arrived during the late 19th century. With the introduction of predators such as cats and stoats, there was a rapid decline in numbers, and by 1950s the kakapo was driven to near extinction.
Today, not more than 85 of these birds survive. Their population is confined to three small islands, which mercifully do not have cats or stoats to prey upon them. However, a as species, the kakapo is critically endangered, because attempts to keep and breed them in captivity have largely been unsuccessful. Their translocation to predator-free off shore islands has definitely given them heedful protection, but that by itself doesn’t ensure the kakapo’s survival. The fate of this bird is inexorably linked to fruiting of the rimu tree, a species of conifer that produces fleshy fruit, rather than cones. Female kakapos need rimu fruit in their food and this fruit is also staple diet of chicks. Usually, the trees produce fruits every three to five years. In the intervening years, the females do not lay eggs. On one island, fruiting did not occur between 1981 and 1997, and the kakapo population was nearly wiped out. If such famines strike again on all three islands, the flightless birds would be doomed forever.
Geographical isolation has worked in the case of the rhea (picture, left) also, the largest South American bird, which stands up to 1.5 metres tall and weighs up to 25 kilograms. Before 7 million years ago, North and South America were separated by ocean, but continental drift brought them together. At first islands formed between them, and then, 3 million years ago, the Isthmus of Panama emerged and
joined the continent. The mammals from each landmass could spread into new territory and compete with species they had never encountered before, But during 60 million years that South America had been isolated, it had developed an ecosystem unlike any other on the Earth. These included, among other creatures, fast- running flightless rheas.
Although these ratites cannot even glide, much less fly, they have rather large wings. The inability to fly is largely compensated by swift running on the ground where the rhea can outdistance the fastest horse. The birds are gregarious, living in flock of 30 or more. The rheas live in grassland and open bush country, feeding on a variety of plant materials including seeds, roots, grasses, leaves and also take animal food such as grasshoppers, molluscs and small vertebrates. They eat almost anything that can be picked up. When a railway was being built in the wilds of South America, there was quite a shortage of nuts and bolts. The rheas used to creep up to the works and steal all that they could find.
These birds are not migratory, but they wander considerable distances on the grasslands of Brazil, Uruguay, Paraguay and Argentina particularly before and after the breeding season. They are preyed upon by larger carnivores. But the adults, with their ability to run fast have a good chance of survival. The young ones, however, are often in peril from eagles and other big birds of prey, which swoop down to carry them off. But the adult rhea is a watchful bird. As soon as it sees a bird of prey appear in the sky, it crouches down and utters a snorting cry. The young ones rush to it for protection, and it shelters them under its stubby wings.
The female rheas of the flock lay their eggs in a single nest. Scores of eggs will be deposited. In one instance, over a hundred eggs were found in the same nest. The male rheas sit on the eggs
till they are hatched. These majestic birds once roamed the South American pampas in huge
flocks, but now they are greatly reduced in numbers due to the spread of agriculture.
By far the largest living bird is the ostrich of the African plains. It weighs about 150 kilograms and is approximately 66,000 times heavier than the smallest hummingbird which weighs 2.25 grams. A full-grown ostrich may be as tall as 8 feet. The theory that geographical isolation has been responsible for grounding some birds like the kiwi does not hold true in the case of the ostrich. After all, the vast continent of Africa can hardly be called an isolated place. Moreover, it has perhaps more than its share of predatory mammals. In the case of the ostrich it has been suggested that the large size of the bird, and perhaps its high running speed, has allowed it to live on without the ability to fly.
As the fastest ratite, the ostrich races away at the speed of 45-48 kilometres per hour for about 20 minutes without showing any sign of fatigue. The maximum speed attained by a frightened ostrich can be considerably more. Years ago, a naturalist once paced an ostrich running paralleled to his Land Rover at 72 kilometres per hour. The bird may have covered 7.6 metres at a single stride.
The ostrich does not run straight, but in curves, which deprives it of much of the advantage derived from speed. The predator, by taking short cuts, can get up to it. Then the ostrich will fight. The strong leg of this bird and its sharp clawed foot are its defense against marauding animals or men. It kicks sideways or forward so powerfully than men and animals have been killed by a blow.
During the breeding season ostriches are seen in groups of one male and four or five females. The females lay their eggs, 40 to 50, in a common nest formed in the sand. At night the male sits on the eggs and the females take turns through the day. Often the male will toss out a few eggs if there are too many in the pit-like nest for comfort. The eggs are up to 20 centimetres long, 15 centimetres in diameter and up to 1.75 kilograms in weight. The shell is 1.5 millimetres thick, but can support the weight of an adult human. Each egg is equivalent in volume to around 24 hen’s eggs.
The largest egg on record weighed 2.3 kilograms and was laid on June 28, 1988 by a two-year-old ostrich at a collective farm in Israel.
In the middle of the nineteenth century, hundreds of thousands of ostriches were raised each year in southern Africa for 1heir ornamental plumes. (European and American women decorated their headgear with ostrich feathers). In the early part of the twentieth century, there were over 7,00,000 birds in captivity and ostrich farms were established in North America, Europe and Australia as well. After the First world war, fashions changed and the industry collapsed. Today, about 25,000 birds are raised primarily for high-quality leather. This flightless bird is a good example of the influence which human beings have on other species. Man’s activities have placed many birds in considerable danger or wiped out quite a few such as dodo, elephant bird and moa. In the case of the ostrich, man’s activities had positive effect. If it were not for the domestication of ostriches, these birds would be on the brink of extinction today.
This flightless Australian bird stands 1.7 metres (5.5 feet) high and weighs about 45 kilograms. with its long legs and lengthy strides; it can run 50 kilometres per hour. Emus lack the graceful plumage of the ostrich, because their feathers resemble shaggy fur. They forage in small groups for insects and fruits, sometimes making booming call through the resonant help of a long inflated air sac in the throat.
The emu has been known to damage agricultural crops. (In the past, whenever large concentrations
of emus created 1 problems various control measures were attempted, but the results were far from satisfactory). The only non-lethal way is to frighten them off with the sound of gunfire. In open regions, however, gunfire merely r disperses the birds and they then r y congregate elsewhere or at the original site when gunfire ceases. In 1932 when emus threatened to become serious pests to wheat growers in
Australia, the government dispatched a machine gun detachment from the Royal Australian Artillery to engage with the enemy. D. L. Serventy, the famous ornithologist, described the result in these words:
‘Emu command had evidently ordered guerrilla tactics and its unwieldy army soon split into innumerable small units that made, the use of military equipment uneconomic.’ So the crestfallen military soon withdrew from the contest.
One noteworthy aspect of emu’s behaviour related to incubation of its eggs. A humming bird may leave its eggs 140 times in one day. Being very small, this bird loses body heat rapidly and must therefore set out to seek food many times a day to make up this energy loss. On the other hand, a male emu in a zoo refused to leave its eggs for nearly 60 days, fasting all the while.
The foregoing description of flightless birds easily leads to the conclusion that in case of emus, kiwis, rheas, ostriches, kakapos, elephant birds, cassowaries and dodos the process of evolution has been retrograde. After all, nothing is more absurd than a flying bird evolving into a flightless one, The great degree of reversal becomes evident when one examines the unique characteristics other birds have gradually acquired through natural selection to become magnificent flying machines.
In order to fly, a bird must solve two basic problems the reduction of weight and the increase of power. Most of the anatomical and physiological differences that set birds apart from other vertebrates seem to be adaptations devoted to the solution of these two problems. They have thin, hollow bones and extremely light feathers. To achieve further weight reduction, they have discarded most skin glands, heavy jaw bones, teeth and tail vertebrae. A system of branching air-sacs adds to their buoyancy and the excretion of concentrated uric acid has averted the need for drinking ample water to produce a larger volume of urine.
To supplement these weight-reducing adaptations, there are various power-increasing adaptations. Although birds evolved from airborne dinosaurs that were most probably cold-blooded, birds have acquired warm bloodedness which makes them agile and energetic. They have heat-conserving plumage which their reptilian ancestors did not have. They have energy-rich diet, rapid and thorough digestion and high glucose content of the blood. A four-chambered heart provides double circulation and there is a highly efficient respiratory system. Also, a high rate of metabolism releases more energy for sustained flight.
It is tempting to think that each of these adaptations is a positive feature, and together, they make flying birds a class apart by themselves. Seen in this light, inability to fly would seem to be a throwback to prehistoric days. However, things are not so simple and evolution works both ways. Discarding a few features here or there is as much of an evolution as acquiring them. By forfeiting their wings, flightless birds have adapted themselves to their isolated environment-and, as Darwin would have readily agreed, it is the adaptation that evolution is all about.