Diversity

objectives

• Describe the relationship between beak shape and diet in birds.

• List 10 major orders of living birds, and name an example of each order.

• Describe the function of the syrinx.

vocabulary

syrinx crop milk

By looking closely at a bird's beak and feet, you can infer many things about where it lives and how it feeds. Hawks and eagles have powerful beaks and clawed talons that help them capture and tear apart their prey. Swifts have a tiny beak that opens wide like a catcher's mitt and snares insects in midair. Because swifts spend most of their lives in flight, their feet are small and adapted for infrequent perching. The feet of flightless birds, on the other hand, are modified for walking and running. Some examples of the variety of bird beaks and feet are shown in Figure 42-8.

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figure 42-8

This cardinal (a), Cardinalis cardinalis, has a short, strong beak for cracking seeds and feet that enable it to perch on small tree branches. This kestrel (b), Falco sparverius, has a beak that enables it to tear flesh and talons that enable it to grip and kill prey. This calliope hummingbird (c), Stellula calliope, has a long, thin beak that enables it to extract nectar from flowers. This northern shoveler (d), Anas clypeata, has a flat beak that enables it to shovel mud while searching for food.

figure 42-8

This cardinal (a), Cardinalis cardinalis, has a short, strong beak for cracking seeds and feet that enable it to perch on small tree branches. This kestrel (b), Falco sparverius, has a beak that enables it to tear flesh and talons that enable it to grip and kill prey. This calliope hummingbird (c), Stellula calliope, has a long, thin beak that enables it to extract nectar from flowers. This northern shoveler (d), Anas clypeata, has a flat beak that enables it to shovel mud while searching for food.

figure 42-9

This mute swan, Cygnus olor, is able to take off from water and fly at very high speeds despite its great weight. Weighing up to 23 kg (50 lb), mute swans are the heaviest flying birds. Swans are monogamous, meaning they mate for life. While the female incubates the eggs, the male helps guard the nest.

figure 42-9

This mute swan, Cygnus olor, is able to take off from water and fly at very high speeds despite its great weight. Weighing up to 23 kg (50 lb), mute swans are the heaviest flying birds. Swans are monogamous, meaning they mate for life. While the female incubates the eggs, the male helps guard the nest.

figure 42-10

The parrot pictured below is a lesser sulfur-crested cockatoo, Cacatua sulphurea. Parrots range in length from 8 cm (3 in.) to over 91 cm (3 ft). The earliest fossils of parrots indicate that they have existed as a group for at least 20 million years. Like most parrots, these cockatoos nest in holes in trees, and they usually lay only two eggs per year. Because of human activities, many species have become extinct or endangered.

Most taxonomists divide about 10,000 species of living birds into 23 orders. Taxonomists have traditionally used morphological evidence from beaks, feet, plumage, bone structure, and musculature to classify birds. Technological advances in the analysis of blood proteins, chromosomes, and DNA have also been used more recently. Despite the introduction of these new methods, the relationships among the 23 orders of birds are still not well resolved. Ten of the most familiar orders of living birds are described below.

Order Anseriformes

Swans, geese, and ducks—commonly called waterfowl—belong to this order of 160 species. Found worldwide, members of this order are usually aquatic and have webbed feet for paddling and swimming. Waterfowl feed on a variety of aquatic and terrestrial foods, ranging from small invertebrates and fish to grass. The bill is typically flattened. The young are precocial, and parental care is usually provided by the female. A mute swan is shown in Figure 42-9.

Order Strigiformes

This order includes the owls, the nocturnal counterparts to the raptors. Owls are predators that have a sharp, curved beak and sharp talons or claws. As shown in the chapter opener photo, owls also have large, forward-facing eyes that provide improved vision at night. Owls rely on their keen sense of hearing to help locate prey in the dark. There are about 180 species of owls, and they are found throughout the world.

Order Apodiformes

Hummingbirds and swifts belong to this order. All of the roughly 430 species are small, fast-flying, nimble birds with tiny feet. Swifts pursue insects and capture them in flight. Hummingbirds eat some insects but also feed on nectar, which they lap up with a very long tongue. The long, narrow bill of a hummingbird can reach deep into a flower to locate nectar. Swifts have a worldwide distribution, but hummingbirds live only in the Western Hemisphere.

Order Psittaciformes

This order includes the parrots and their relatives, the parakeets, macaws, cockatoos, and cockatiels. Most of the roughly 360 species in this order live in the tropics. Parrots are characterized by a strong, hooked beak that is often used for opening seeds or slicing fruits. Their upper mandible is hinged on the skull and movable. Unlike most birds, parrots have two toes that point forward and two toes that point toward the rear, an adaptation for perching and climbing. They are vocal birds, and many species gather in large, noisy flocks. Parrots have long been prized as pets because of their colorful plumage and intelligence and because some species can be taught to mimic human speech. However, habitat destruction and excessive collecting for the pet trade now threaten many parrot species with extinction. Figure 42-10 shows a cockatoo.

figure 42-11

Toucans, such as this keel-billed toucan, Ramphastos sulfuratus, mate once per year, usually laying two to four eggs. The male and female toucans take turns sitting on the eggs. The eggs usually hatch after about 15 days of incubation.

Order Piciformes

This diverse group of tree-dwelling birds contains woodpeckers, honeyguides, and toucans. All members of this order nest in tree cavities. Like parrots, they have two forward-pointing toes and two that point to the rear. There are about 350 species found throughout the world except in Australia. The diversity of foods consumed by these birds is reflected in the diversity of their bills. Woodpeckers, which drill holes into trees to capture insects, have strong, sharp, chisel-like bills. Toucans feed mainly on fruit, which they pluck with a long bill, as shown in Figure 42-11.

Order Passeriformes

This large order contains about 5,900 species—more than half the total number of bird species—and includes most of the familiar North American birds. Robins, warblers, blue jays, and wrens are just some of the birds belonging to this group.

Passerines are sometimes called perching birds. In most birds, three toes point forward and one points backward. Passerines, too, have this arrangement of toes, but the rear toe is enlarged and particularly flexible to provide a better grip on branches. Passerines feed on a variety of foods, including nectar, seeds, fruit, and insects.

Many passerines are called songbirds because the males produce long, elaborate, and melodious songs. Male birds sing to warn away other males and to attract females. The song is produced in the structure known as the syrinx (SIR-ingks), which is located at the base of the bird's trachea. By regulating the flow of air through the syrinx, birds can generate songs of great range and complexity.

Order Columbiformes

This globally distributed group contains about 320 species of pigeons and doves. Figure 42-12 shows a mourning dove. These birds usually are plump-breasted and have relatively small heads; short necks, legs, and beaks; and short, slender bills. Most feed on fruit or grain.

The crop, which in most other birds is used to store food, secretes a nutritious milklike fluid called crop milk. Both sexes produce crop milk to feed their young. Columbiform birds usually lay a clutch of two eggs, which hatch after a two-week incubation period. The young usually leave the nest two weeks after hatching. Another member of this order is the now-extinct dodo of Mauritius, an island in the Indian Ocean.

Order Ciconiiformes

The order Ciconiiformes is highly diverse, and has a worldwide distribution. This order includes about 1040 species of herons, storks, ibises, egrets, raptors, and penguins. Many have a long, flexible neck, long legs, and a long bill. Many are wading birds, and they feed on fish, frogs, and other small prey in shallow water. Many species of Ciconiiformes are diurnal (daytime) hunters with keen vision. Vultures, however, feed on dead animals and use their sense of smell to detect the odor of decomposing flesh.

figure 42-11

Toucans, such as this keel-billed toucan, Ramphastos sulfuratus, mate once per year, usually laying two to four eggs. The male and female toucans take turns sitting on the eggs. The eggs usually hatch after about 15 days of incubation.

figure 42-12

The adult mourning dove, Zenaida macroura, stands about 30 cm (12 in.) tall and nests in trees or bushes. Mourning doves breed throughout North America. They winter as far south as Panama.

figure 42-13

The great blue heron, Ardea herodias, uses its spearlike beak to stab fish, frogs, and other prey. Young herons must be taught how to hunt. Scientists have learned that young herons often miss their intended prey and must also learn what is and is not food.

figure 42-13

The great blue heron, Ardea herodias, uses its spearlike beak to stab fish, frogs, and other prey. Young herons must be taught how to hunt. Scientists have learned that young herons often miss their intended prey and must also learn what is and is not food.

Word Roots and Origins syrinx from the Greek syrinx, meaning "reed" or "pipe"

Raptors have a sharp, curved beak and sharp talons and include ospreys, hawks, falcons, vultures, and eagles. About 310 species of raptors are distributed throughout the world. Some members of this order grow to be quite large. Figure 42-13 shows a great blue heron, a large species that is in North America. The marabou stork of Australia, for example, can be more than 1.5 m (59 in.) in height.

Penguins are a unique group of flightless marine birds. All 17 species live in the Southern Hemisphere. The penguin's wedge-shaped wings have been modified into flippers, and the feet are webbed. Underwater, penguins flap their flippers to propel themselves forward—they "fly" through the water. Most penguins have a thick coat of insulating feathers and a layer of fat beneath the skin, enabling them to live in polar conditions. They maintain this fat layer by consuming large quantities of fish and krill.

Order Galliformes

Members of this group, which includes turkeys, pheasants, chickens, grouse, and quails, are commonly called fowl. These terrestrial birds are usually plump-bodied and may have limited flying ability. Grains form a large part of the diet of many fowl, and all species have a large, strong gizzard. Some are also an important part of the human diet. The young are precocial. There are about 220 species distributed worldwide.

Order Struthioniformes

Some of the world's largest birds belong to this order. They include ostriches, rheas, emus, and cassowaries. Ostriches are native to Africa and can attain a height of nearly 3 m and weigh 150 kg. Ostriches cannot fly, but they are specialized as high-speed runners. Propelled by their long, strong legs, ostriches can reach speeds of 55 km per hour. Each large foot has only two toes. Reduction in the number of toes is common in running animals.

Rheas are a South American version of the ostrich. Emus are the second largest of the world's birds, originally found in Australia. Cassowaries, from New Guinea, are the most colorful of this order, with black bodies and blue heads.

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