Flightless Birds

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Flightless Birds

Ratites are flightless birds that lack the keel (high ridge) on the breastbone to which the flight muscles of flying birds are attached. Instead, the entire breastbone looks rather like a turtle’s shell. It has also been described as a raft, which gives this group of flightless birds its name, Ratitae (ratis means raft in Latin). Ratites have heavy, solid bones, while flying birds have lightweight, hollow ones. Several ratites, such as ostriches, rheas, emus, and cassowaries, are the largest living birds. The kiwis of New Zealand, however, are about the size of chickens.

These flightless birds are the oldest living birds. All older species of ratites are now extinct. However, several ratite species became extinct only recently. Genyornis of Australia survived long enough to be hunted by aborigines about 30,000 years ago. The largest bird ever found, the elephant bird or roc (Aepyornis ), lived in Madagascar. A huge New Zealand moa (Dinornis ), which became extinct only about 200 years ago, may have been as tall, but did not weigh as much as the roc. The moa had no wings at all.

Although ratites are the most ancient of the living birds, they are no more closely related to the reptiles from which they evolved than other birds are. In fact, they are probably descended from flying birds. Their ancestors lost the ability to fly because they did not need to fly to obtain food or escape from predators. They probably had no important enemies in their habitats.

The structure of their feathers also prevents ratites from flying. On a flying bird’s feathers, the barbs, those branches that grow at an angle from the shaft (or quill), are fastened together by hooked structures called barbules. This design makes a smooth, flat, light surface that can push against the air during flight. The feathers of ratites, however, lack barbules. The strands that grow from the quill separate softly, allowing the air through. This quality of softness is what makes the feathers of many ratites particularly desirable. Ostrich plumes, for example, have long been used as decoration on helmets and hats.

The living flightless birds are classified by some taxonomists into four orders (Struthioniformes, Rhei-formes, Casuariiformes, and Apterygiformes) and five families, while other taxonomists place all these large birds in a single order, the Struthioniformes. The single species of ostrich is in the family Struthionidae. The two species of rhea are in the family Rheidae. Emus belong to the family Dromaiidae, while cassowaries comprise the family Casuariidae. Kiwis belong to the

family Apterygidae. Some ornithologists consider the tinamous of Central and South America to be ratites because they seldom fly. However, tinamous are capable of flight (although they prefer to run from predators and other danger) and have keeled breastbones. Penguins are also flightless birds, but they are not regarded as ratites. Their powerful breast muscles are used for swimming instead of flying.

Ostriches

The ostrich is Earth’s largest living bird. There is only one species, Struthio camelus. The specific name comes from the fact that these tall, desert-living birds have been called camel birds. They may be as much as 8 ft (2.4 m) tall and weigh up to 400 lb (181 kg). A prominent distinction among subspecies of ostrich is skin color. The long legs and long, straight neck show red skin in some subspecies and blue in others.

Natives of Africa, ostriches are found on the dry plains, where they seem more at home among big mammals, such as giraffes, than they do among other birds. They are currently found in three areas: Western Africa, at the farthest western portion of the bulge; South Africa; and in East Africa from the Horn of Africa (Ethiopia). They were formerly found on the Arabian Peninsula, but this subspecies was hunted for sport and became extinct during the first half of the twentieth century. An effort is being made to re-introduce ostriches to this region, although of a different subspecies.

Generally, ostriches have whitish neck, head, and underparts, with a thick covering of black or dark-brown feathers crowning the entire back. The female’s feathers are almost uniformly brown, while males have a black body with white wing and tail feathers. Ostrich plumage seems almost more like fur than feathers. Ostrich plumes, especially the long ones from the birds’ tail and wings, have been popular for centuries, primarily for use on hats. Today, their softness makes them useful for dusting and cleaning delicate machine parts.

Ostriches have scaly legs and feet. There are only two toes on each foot, both of which hit the ground when the bird walks. Each toe ends in a thick, curved nail that digs into the soil as the ostrich runs. One toe is immense, almost the size of a human foot; the other is much smaller. Each toe has a thick, rough bottom that protects it.

There is a myth that ostriches put their heads in the sand when frightened, but this is not actually the case. In reality, ostriches can run faster than just about any predator, or they can stand their ground and kick with powerful slashing motions of their sharp-nailed feet. Ostriches can run at a steady pace of about 30 mph (48 km/h), with a stride that can cover more than 20 ft (6 m). At top speed for a brief time, they can run almost 45 mph (72 km/h).

There is little up and down motion as they run. Instead, their legs handle all of the motion and their body stays in one plane. Ostriches, as well as the slightly smaller rheas, use their wings rather like sails. When running, they hold them out from their bodies. This helps them balance and, by changing the level of one wing or the other, it helps them easily change direction as they run. If frightened, a running ostrich may swerve into a circular pattern that takes it nowhere.

These large birds have been farmed for more than 150 years, starting in Australia. Originally the birds were raised just for their plumes, but in recent years they have been raised for their large eggs, their skin, which tans into attractive leather, and their meat. The feathers are actually harvested, in that they are cut off before falling out as they would naturally. This harvesting keeps them from being damaged. New feathers grow in to replace the harvested ones.

Ostriches have the largest eyes of any land animal—a full 2 in (5 cm) in diameter. The eyes are shielded by eyelash-lined outer eyelids that blink from the top downward, as well as nictitating membranes that close from the bottom of the eye upward. This membrane protects the eye, but is semitransparent so that the bird can still see.

Because a tall ostrich may get the first sight of approaching danger on the savanna, its alarm may alert other animals to the presence of danger. The birds are usually left undisturbed by herding mammals. The ostriches act as lookouts and the mammals stir up insects and other small animals with which the ostriches supplement their herbivorous diet. Actually, ostriches will eat just about anything, especially if it is shiny and attracts their attention.

During the dry season, herds containing as many as 500-600 ostriches may gather at a watering hole. The males, or cocks, tend to stay in one group, while the females, or hens, stay in their own groups. When the rainy season begins, however, they split into harem groups, consisting of one male and two to four females.

A male ostrich performs a courtship dance involving considerable puffing and strutting, accompanied by booming noises. At its conclusion, he kneels and undulates his body in front of his chosen female. If she has found the performance enchanting, she also bends her knees and sits down. The male’s dance may be interrupted by a competing male. The two males then hiss and chase each other. Any blows are given with their beaks.

The male selects the nesting site for his several females. He prepares it by scraping a slight indentation in the soil or sand. The dominant female lays her eggs first, followed by the others, over a period of several weeks. Altogether, there may eventually be as many as 30 off-white, 8 in (20 cm) eggs in a single clutch, perhaps half of them belonging to the dominant female. However, not all the eggs will hatch because they cannot all be incubated. Abandoned eggs do not attract many scavengers because the shells are too thick to break easily.

Both the dominant female and the male take turns incubating the eggs, with their insulating feathers spread over the nest. The sitter also takes time to turn the eggs on a regular basis. The eggs hatch about six weeks after the start of incubation, but the hatching may be a slow process because the chicks are able to break only tiny bits of the tough shell at a time. The mottled-brown chicks, each about 1 ft (30.5 cm) tall, are tended by all the females in the group. The chicks are ready to feed on their own, but are protected by the adults as they grow. They develop adult feathers by their third year, and soon afterward are mature enough to mate. Ostriches can live to be more than 40-50 years old.

Rheas

Rheas are similar in appearance to ostriches, but they are smaller and live in South America instead of Africa. The two species of rheas, often called South American ostriches, vary in size and location. The common or greater rhea (Rhea americana ) of Argentina and Brazil stands 5 ft (1.5 m) tall, several feet shorter than an ostrich, but it is still the largest North or South American bird. The lesser or Darwin’s rhea (Pterocnemia pennata ) of southern Peru to the Patagonian region of Argentina is considerably smaller and has white tips on its brown plumage. Rheas live on open grassy plains in most of South America except the Andes Mountains and the northeastern region along the Atlantic. They can usually be found in flocks of about 50 birds, often in the vicinity of cattle herds.

Rhea males attract females by swinging their heads from side to side and making a loud, roaring sound. The females are mute. Unlike ostriches, a rhea male lines the nest with leaves and assumes total responsibility for incubating the eggs. The male incubates the eggs of five or six females for about five weeks, and then takes care of the young. The eggs are dark green, almost black, in color.

Emus

The single living species of emu (Dromaius novae-hollandiae ) looks very much like an ostrich but without the long neck. This Australian bird stands between the ostrich and rhea in height, about 5-6 ft (1.5-1.8 m) tall. It has a black head, long, brown body feathers, and white upper legs. Its feathers are unusual in that two soft feathers grow out of only one quill. Only the emu and the related cassowary have feathers like this. The emu’s plumage droops downward, as if from a central part along its back.

Emus live on the open dry plains of central Australia. They do not stay in one place, but migrate several hundred miles as the seasons change. Emus spend the cold, dry season in the south, and then return north when the rains start. As they travel, they communicate with each other by powerful voices that boom across the plain.

An emu male chooses only one mate. She lays a dozen or more dark green eggs, but then the male sits on them for the eight-week incubation period. The chick has lengthwise white stripes on its brown body and a speckled brown and white head. The male protects the chicks until they are about six months old and can defend themselves against predators.

Until the early nineteenth century, there were two other species of emus living on the islands near Australia. However, they were killed for their meat and are now extinct. On the mainland, emus were plentiful, so plentiful that in the 1930s, Australian farmers started a campaign to exterminate emus because they competed for grass and water needed for cattle and sheep. But the birds’ ability to run or blend with the surroundings, plus some ineptness on the part of the farmers, allowed the emus to survive. Even in the early 1960s, emu hunters could still collect a payment from the government for each bird they killed. However, that changed as Australians began to value the uniqueness of this bird. Now the emu and the kangaroo are featured on Australia’s coat of arms.

Cassowaries

The three species of cassowaries (Casuarius ) are found only on the island of New Guinea and the nearby portion of Australia. They are about the same height as a rhea and weigh about 185 lb (84 kg). However, all resemblance ends there. The southern, or Australian, cassowary (C. casuarius ) has a vivid blue, featherless head rising from a red-orange neck. Two flaps of flesh, called wattles, hang from the neck, as on a male turkey. The wattles can be almost red, green, blue, purple, or even yellow. The body is covered by a thick coat of shiny, black feathers. The one-wattled cassowary (C. unappendiculatus ), as its name suggests, has only one wattle. Bennett’s cassowary (C. bennetti ) is considerably smaller and lacks the wattles. The female cassowary is larger than the male. This is the only large flightless bird that lives in forests instead of on open plains.

On top of a cassowary’s head, stretching down over the base of the beak, is a bony protuberance called a casque, which means “helmet.” A cassowary thrusts its casque out in front of it when it runs through the forest. Its unusual wing feathers also help it move through the forest. The cassowary’s wings are almost nonexistent, but from them grow several quills that lack barbs. These bare quills stretch out beyond the other feathers on each side and serve to help push obstructions aside. Cassowaries eat mainly fruit that has fallen from trees, along with leaves and some insects.

Cassowaries live alone instead of in flocks and are nocturnal. A male and a single female come together only at mating time, when the female lays three to eight dark green eggs. The male incubates the eggs and then takes care of the young. The young cassowaries are striped from head to tail, even more vividly than the emu young.

Kiwis

Kiwis are three species of small, forest-dwelling, flightless birds that live only in New Zealand. The body length of kiwis ranges from 14-21 in (35-55 cm), and they typically stand about 15 in (38 cm) tall. Adult birds weigh 3-9 lb (1.5-4 kg). Kiwis have a rounded body with stubby, rudimentary wings, and no tail. Their legs and feet are short but strong, and they have three forward-pointing toes as well as a rudimentary hind spur. The legs are used in defense and for scratching about in the forest floor while feeding.

The bill is long, flexible, slightly down-curved, and sensitive; it is used to probe for earthworms and insects in moist soil. Their nostrils are placed at the end of the beak. Kiwis appear to be among the few birds that have a sense of smell, useful in detecting the presence of their invertebrate prey. They snuffle as they forage at night, and their feeding grounds are recognized by the numerous holes left by their subterranean probings.

Kiwis have coarse feathers, which are hairlike in appearance because they lack secondary aftershaft structures, such as barbules. Their shaggy plumage is brown or gray. The sexes are similar in color, but the female is larger than the male.

Kiwis lay one to two eggs, each of which can weigh almost 1 lb (0.5 kg), or about 13% of the weight of the female. Proportionate to the body weight, no other bird lays an egg as large. The female lays the eggs in an underground burrow—a cavity beneath a tree root, or a fallen log. The male then incubates them. The young do not feed for the first six to twelve days after hatching, and they grow slowly thereafter. Kiwis reach sexual maturity at an age of five to six years.

Kiwis are solitary, nocturnal birds. Because of the difficulties of making direct observations of wild kiwis, relatively little is known about these extraordinary birds. Kiwis make a variety of rather simple whistles and cries. Those sounds of male birds is two-syllabic, and sounds like “ki-wi.” Obviously, this bird was named after the sound that it makes.

The brown kiwi (Apteryx australis ) is the most widespread species, occurring in moist and wet native forests on South and North Islands, New Zealand. The little spotted kiwi (Apteryx owenii ) is a gray-colored bird, while the great spotted kiwi (A. haastii ) is more chestnut-colored, and larger.

Kiwis are the national symbol of New Zealand, and New Zealanders are commonly known as “kiwis.” However, because these birds are nocturnal and live in dense forest, relatively few human “kiwis” have ever seen the feathered variety. Unfortunately, kiwis have suffered severe population declines over much of their range. This has been caused by several interacting factors. First, like other flightless birds (such as the

KEY TERMS

Barb —The branches of a feather, growing out of the quill and sometimes held together by hooked barbules. Ratites’ barbs are not held together.

Barbule —Hooks that hold the barbs of a feather together in flying birds.

Casque —The triangular bony growth that projects from the skull of a cassowary and stretches down over half the beak.

Keel —The ridge on the breastbone of a flying bird to which flying muscles are attached.

Nictitating membrane —A membrane that can cover the eye of some animals, in addition to the regular eyelid. It provides protection but still allows the animal to see.

Quill —The central shaft of a feather, generally hollow, from which the barbs grow.

extinct moas of New Zealand), kiwis were commonly hunted as food by the aboriginal Maori peoples of New Zealand. The feathers of kiwis were also used to ornament the ceremonial flaxen robes of the Maori. After the European colonization of New Zealand, settlers also hunted kiwis as food, and exported their skins to Europe for use as curiosities in the then-thriving millinery trade.

The excessive exploitation of kiwis for food and trade led to a rapid decline in their populations, and since 1908 they have been protected by law from hunting. However, some kiwis are still accidentally killed by poisons set out for pest animals, and they may be chased and killed by domestic dogs.

Kiwis have also suffered greatly from ecological changes associated with introduced mammals, especially species of deer. These invasive, large mammals have severely over-browsed many forests where kiwis live, causing habitat changes that are unfavorable to the bird, which prefers dense woody vegetation in the understory. Deer are now regarded as pests in New Zealand, and if these large mammals were locally exterminated, this would markedly improve the habitat available for kiwis and other native species. The little spotted kiwi has suffered most from these habitat changes and is currently confined to four island sanctuaries where predators have been or are being removed. Fortunately, the conservation efforts of the government and people of New Zealand appear to be successful in their efforts to increase numbers of kiwis. These birds are now relatively abundant in some areas.