Getting to Know Birds
It is easy to tell that an animal is a bird. If it has feathers, it is one of the more than 8,600 kinds of birds in the world. Birds can also be recognized by their bills, wings, and two legs, but feathers are what make them different from every other animal.
Scientists are not sure when feathers first appeared on animals. They might have begun as feather-like scales on some of the dinosaurs. In 1861, fossils of a feathered animal, Archaeopteryx (ar-key-OP-tuh-rix), were found in Germany. These are the first animals known to scientists that were covered with feathers. These crow-sized animals with heads like lizards lived on the Earth about 150 million years ago.
How birds use different types of feathers
Feathers in most birds' wings and tail help them fly. Each of these flight feathers has a stiff shaft that goes from one end to the other. Flight feathers are light, but they are surprisingly strong. Birds that can fly can escape enemies and get to food sources and nesting places they wouldn't be able to walk to.
Feathers have many other uses in addition to flight. The outer feathers on a bird's body give it color and shape and help to waterproof the bird. Outer feathers with patterns are useful for camouflaging some birds, and colorful feathers send messages. For example, male birds show off their bright feathers to impress females or wave them as warnings to others. Downy inner feathers trap air to keep the bird warm.
Scientists have names for different types of feathers and also for groups of feathers according to where they grow on a bird's body.
Most birds' bodies are built for flight. Air sacs in their chests and hollow bones keep them light. They have powerful chest muscles that move their wings. The wing and tail feathers are tough, and birds can turn some of them for steering. A bird usually shuts its wing feathers to trap the air as its wings go down. This lifts the bird into the air and pushes it forward. Then, as it raises the wings, it fans the feathers open to let the air through.
How birds fly depends somewhat on the shape of their wings. Vultures and seabirds have long, narrow wings that are great for soaring high on air currents or gliding over the ocean. Songbirds have short, broad wings that are made for flapping as the birds fly among trees. Falcons have narrow, pointed wings that curve backward. These wings help them fly fast and steer well. But all birds flap their wings at times and glide at other times, depending on what they are doing and how the wind is blowing.
Some birds use their wings in unusual ways. Hummingbirds can flap their wings about fifty times every second. This allows them to hover at one spot as they lap nectar from flowers. Flipper-like wings help penguins to "fly" through the water, and even ostriches use their wings to keep their balance as they run.
The wing of a bird is rounded on top and flat on the bottom, similar to the wing of an airplane. This shape is what gives the bird the lift it needs to stay up in the air.
Birds take off and land facing the wind. Small birds (up to the size of pigeons) can jump up from the ground and fly right off into the air. Larger birds have to jump off something high or run along the ground or the water to get going.
Different, but the same
A 400-pound (181-kilogram) ostrich may seem very different from a tiny bee hummingbird that weighs less than an ounce (about 2 grams). But all birds have many things in common besides having feathers. They have bills, two legs, a backbone, they are warm-blooded (keep an even body temperature), and they lay hard-shelled eggs.
Birds have many different shapes. Wading birds such as flamingos have long necks and long legs. Eagles have short necks and legs. But both kinds of birds are able to find their food in the water. Falcons and penguins have sleek, torpedo-shaped bodies that are perfect for catching speedy prey. Turkeys' heavier bodies are just right for their quiet lives in the forest searching for acorns and insects.
Bird bills come in a wide variety of shapes. They use their bills to gather food, build nests, fix their feathers, feed their young, attract mates, and attack their enemies. The type of food a bird eats depends on its bills' shape. For example, the sturdy bills of sparrows are good for cracking seeds, and hawks' hooked beaks are perfect for tearing up prey.
Legs and feet
Bird legs and feet fit their many different lifestyles. For example, hawks have sharp talons for hunting and ducks have webbed feet to help them swim. Some of the birds that spend most of their lives in the air or on the water are not good at walking. Most birds have four toes, but some have three, and ostriches have only two.
For most birds, sight is their best sense. They can see much better than humans, and they can see in color, unlike many mammals. A bird's eyes are big and are usually set on the sides of its head. The eyes focus independently, so that the bird sees two different things at the same time. This gives the bird a very wide view and helps it to watch for predators in most directions. Most birds cannot roll their eyes, but they can turn their heads farther around than mammals can. Owls and other birds of prey have forward-facing eyes that usually work together. This helps them judge distance as they swoop down on prey.
Birds have a good sense of hearing—they can hear about as well as mammals. The sound goes in through a little opening near each eye. The holes are usually covered with feathers. They lead to the bird's middle and inner ear, which are very sensitive to sounds. Because owls hunt at night, hearing is especially important to them. Some owls have a disc of stiff feathers on the face. The disc catches sounds, such as the squeaks of a mouse, and leads them to the ears.
Birds have many nerve endings, which shows that they have a good sense of touch. They can also feel pain, hot, and cold. Some long-billed birds have very sensitive bills and can feel their prey in muddy water.
Smell and taste
Most birds' sense of smell seems to be poorly developed. But kiwis, turkey vultures, and several other birds are able to find food by sniffing it. Although birds do not have many taste buds on their tongues, they can often taste well enough to avoid eating harmful foods.
Organs and muscles
Birds have many of the same organs that humans have, but they have special features that help with flight and keep them light. Their biggest, strongest muscles control their wings. Birds do not have a heavy jaw with teeth to grind their food. Instead, it is ground up in a muscular stomach called a gizzard, and they swallow gravel to help with the grinding. To get the energy they need for flight, birds digest their food quickly. Their fast digestion also keeps them from being weighed down for long by the food they have eaten.
A birds' skeleton is strong, even though it light. Many of the bones are hollow, and some of them are joined together to give the skeleton extra strength. (Loons and other diving birds have some solid bones to help the birds sink in the water.) The breastbone, or sternum, of a flying bird has a part called the keel. The bird's big flight muscles are attached to the keel. What looks like a backward-bending knee on a bird is really its ankle. The bird's knee is hidden high up inside its body feathers.
Birds are warm-blooded, which means their bodies stay at an even temperature no matter how warm or cold it is outside. They make their own heat from the food that they eat. Some birds cope with cold weather by growing extra feathers or a layer of fat, fluffing their feathers to trap more air, and huddling together with other birds. When birds can't find enough food to keep warm, they fly to warmer places. In hot weather, they cool down by panting, swimming in cool water, sitting in the shade, and raising their wings to catch a breeze.
Singing is one of the most important ways that songbirds communicate. Birds do not sing just because they are happy. Instead, a male songbird sings to say that he "owns" a certain territory, and he warns birds of the same species to stay away. Songbirds do not have to see each other to know who is nearby. Birds can recognize the songs of their neighbors, because each bird of the same species sounds a little different. Male birds show off to females by singing the most complicated songs they can. Often the best singers are the strongest, healthiest males. When a female songbird hears her mate singing, her brain tells her body to make hormones (special chemicals). These hormones make eggs start to grow inside her body.
Other ways birds communicate
Singing is just one of the many ways that birds communicate with each other. They have warning calls that tell other birds that a predator is nearby. They chirp to say, "I am here, where are you?" And young birds sometimes beg noisily to be fed. At breeding time, birds have a variety of courtships displays that ask, "Will you be mine?" and state, "We belong together." These include bowing, flight displays, and calling together. Male birds parade and show off bright feathers or blow up colorful throat sacs to impress females.
When a bird has found a mate, it is nest-building time. Birds lay their hard-shelled eggs where they can be protected from predators and rain. There are many different kinds of nests. Some birds lay their eggs right on the ground or on the sides of cliffs, some use tree holes or burrows, and some weave complicated stick nests. A few kinds of birds even bury their eggs in mounds of soil and leaves.
Eggs and hatching
Eggs come in many different sizes and colors. Those laid on the ground usually have camouflage colors, and eggs laid in hidden places are often white. The female bird usually incubates the eggs (keeps them warm), especially if she has duller, harder-to-see feathers than the male. Sometimes males and females take turns, and occasionally the males incubate by themselves. Some birds, such as cowbirds, lay their eggs in the nests of other bird species and let the other birds incubate them.
Growth of young birds
There are two main types of newly hatched birds. Young chickens, ducks, geese, turkeys, and ostriches are precocial (pre-KOH-shul). Precocial chicks are covered with down feathers and can run or swim after their parents soon after hatching. Before long, they learn to find their own food, but the parents usually protect them for a while longer. Altricial (al-TRISH-ul) birds are helpless when they hatch. Songbirds, seabirds, owls, parrots, and woodpeckers are some of the altricial birds. They are naked, blind, and weak, and they need to be fed by adults at least until they leave the nest.
HABITS HABITATS AND PEOPLE
Surviving in a habitat
In order to live in a habitat, birds need food, water, and shelter (such as a hedge to hide in). At breeding time, they also need a place to raise their young. Many different kinds of birds can live in the same habitat because they eat different foods and nest in different places. Some birds, such as crows, can often adapt to changes in their habitat, but other birds are very particular and have to leave if something changes.
Staying alive and keeping fit
Birds have to have their feathers in flying shape at all times so that they can escape predators. Well-cared-for feathers are also necessary for keeping the birds warm and waterproof. Birds often have to stop what they are doing and take time out to fix their messed-up feathers. Sometimes they start with a bath. But they always finish by preening. To preen, the birds nibble along each feather to remove dirt and tiny pests. Most birds also get oil on their beaks from a gland near their tails. They spread the oil on each feather and straighten it by zipping it through their beaks. The oil keeps the feathers from drying out and waterproofs them. When a feather gets too worn, it either falls out or gets pushed out by a new feather growing in its place.
Migration is one way birds cope with natural changes in their habitats. When the weather gets cold and insects get scarce in fall, for example, insect-eating birds fly to warmer places where they will be able to find the food they need. Their bodies are programmed to tell them that when the days start getting shorter, they have to eat more so they will have enough fuel for the journey. They follow the same migration routes year after year, and they know the general direction they should go and where to stop. The migrating birds are guided by the stars and by the direction the sun moves across the sky. Birds have a built-in compass and are able to follow magnetic fields in the earth. Some birds also rely on landmarks such as rivers and mountains to follow, and some may use sounds and smells to help them find their way.
Birds and people
Birds are some of the most visible wild animals on Earth, and they play an important part in people's lives. Humans learned about flight from birds, they eat birds and their eggs, and they keep birds as pets. They appreciate the way birds eat insect pests and weed seeds, and they enjoy watching and listening to birds. Sometimes people kill the birds that eat fish or destroy their crops. People have also harmed birds unintentionally by polluting their habitats or turning them into farms and cities.
Humans now take the disappearance of birds from an area as a warning—there may be harmful poisons in the air or water. Many people are working hard to preserve natural places for birds and all wild animals. They are also having some success with fixing habitats that have been destroyed, but fixing them is much harder than preserving them in the first place.
FOR MORE INFORMATION
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Proctor, Noble S., and Patrick J. Lynch. Manual of Ornithology, Avian Structure and Function. New Haven, CT: Yale University Press, 1993.
Reid, Struan. Bird World. Brookfield, CT: The Millbrook Press, 1991.
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Sibley, David Allen, Chris Elphick, and John B. Dunning, Jr., eds. National Audubon Society: The Sibley Guide to Bird Life & Behavior. New York: Alfred A. Knopf, 2001.
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