Birds are part of the animal kingdom and are found everywhere on earth. They are warm- blooded, which means they can keep a warm body temperature constantly, even if their surroundings are cold. There are about 9,000 different species, or kinds, of birds. They are grouped into about 150 families.

Body

Bird skeleton ©Getty Images

Bird skeleton ©Getty Images

Bones

Birds are vertebrates, meaning they have a backbone. Some bones in a bird's skeleton are fused, or joined so that they are like one bone, which strengthens the skeleton for flying. Bird bones are hollow but strong, so the bodies of flying birds are light in comparison to their size.

Heart and Lungs

In flight, birds use a lot of oxygen. For that reason, they have a powerful heart that beats more frequently than human hearts do. Birds breathe differently from other animals with lungs. Their lungs are quite small and tube-like, but air sacs keep the lungs permanently inflated even when the bird is breathing out. Air flows first to the air sacs, which send oxygen-filled air into the lungs. This provides birds with plenty of oxygen.

A wedge-tailed eagle, Australia's largest bird of prey ©Getty Images

A wedge-tailed eagle, Australia's largest bird of prey ©Getty Images

Eyesight

Birds have excellent eyesight, and this helps them find food, especially birds that fly at great heights, such as birds of prey.

 

 

 

Beaks

A beak that opens Brazil nuts...a young green winged macaw ©Getty Images

A beak that opens Brazil nuts...a young green winged macaw ©Getty Images

There is a huge variety of beak shapes among birds, for different purposes. For example, the hooked beak of an eagle helps it tear meat from bones, while the differently hooked beak of a parrot helps it crack open nuts to eat the seed inside. Honey eaters have long thin beaks that fit inside a flower to reach the nectar. Some honey eaters have beaks designed to fit specific flowers that no other nectar eater can reach. Some wading birds have long sharp beaks that reach down into the water to stab a fish. Pelicans have a whole fishing basket attached to their lower beak. Beaks are also used for defence, gathering materials for nests, nest building, cleaning feathers and courting.

Diet and Digestion

A tiny hummingbird getting nectar. ©Getty Images

A tiny hummingbird getting nectar. ©Getty Images

Birds use a great deal of energy, especially for flying. They spend a great deal of their time looking for food to supply that energy. Some birds, such as eagles, falcons and penguins are carnivores. Some birds are herbivores, such as parrots, honeyeaters and finches, that eat plants or parts of plants, such as seeds, nectar and fruit. Some birds, such as emus and starlings, are omnivores because they eat plants and meat.

Birds do not have teeth, although their ancestors did. The food they swallow goes into a crop, where it is stored until it travels to the gizzard, which is made of muscle, and contains small stones and grit that the bird has swallowed. These grind up the food. A bird's tongue has a bone inside it. Tongues help a bird drink, and to hold and tear food. Depending on their diet, birds play an important part in the environment. Carnivorous birds clean up the carcasses of animals that have died or have been killed on the roads or have died in the wild. Other birds help keep insects under control, or spread pollen between flowers. The Rainbow Lorikeet has a brush-tipped tongue to help collect and spread pollen from the flowers it feeds on.

Feathers

Different kinds of feathers ©Getty Images

Different kinds of feathers ©Getty Images

Birds are the only animals covered with feathers. The feathers of male birds are usually more colourful than those of the females, who need camouflage when sitting on the nest. The ancestors of birds were dinosaur reptiles, and feathers are actually modified scales. Birds still have scales on their legs and feet.

Feathers grow quickly. They seal off at the base of the shaft, where each has a muscle attached so that each can move and be kept in place. Birds lose feathers once or twice a year. Each is replaced with a strong new feather. This process is called 'moulting'.

Tail feathers of a peacock. The peahen is brown. ©Getty Images

Tail feathers of a peacock. The peahen is brown. ©Getty Images

There are different kinds of feathers. The largest are contour feathers. They give a bird its shape and colour, and include the the flight feathers on the wings and tail. The wing flight feather is not exactly symmetrical because the part that faces forward, called the leading edge, gets more pressure than the edge that trails.

The rest of the contour feathers are the ones that give the bird's body its shape, which varies with different types of bird. They provide important defence against objects and weather. They have strong shafts and side branches called barbs. The barbs are lined with tiny hooks called barbules, which keep the barbs together.

Also important are the small soft, fluffy feathers called down. They don't have barbules and little hooks. Down grows close to the skin and keeps a bird from getting too hot or too cold.

The other kinds of feathers are:

  • Semiplumes are between the contour feathers and help provide insulation and shape.
  • Filoplumes are smaller, and have only a few barbs at the tips. It is thought that they help birds keep their feathers in order.
  • Bristles are small and stiff with no barbs. They are around the mouth and eyes of some birds, probably for protection.
  • Powder feathers grow continuously and are scattered through the feathers of most birds. They help keep the feathers clean. The barbs at the tip break down into fine powder that some birds use to mop up slime and dust that gets on the other feathers.

Flight

Aerofoil shape of a bird's wing. ©Getty Images

Aerofoil shape of a bird's wing. ©Getty Images

All birds have wings, but not all birds fly. Most birds do fly, but some run fast or swim well, on or under the water. Many birds can do various combinations of these.

To assist with flying, there are two main flight muscles on each wing,and 48 other muscles within the wings and shoulders.

It is the shape of a bird’s wing that helps it fly. The shape of the wing is called an aerofoil: the wing isn’t flat, but curved. Air splits in two around the wing : some passes over the top of the wing and the rest passes underneath. The air going above has further to go and speeds up. The air passing below the wing goes slower, causes more pressure and pushes the wing up. So air moving over the wings pulls the bird up and air moving below pushes the bird up. 

In addition to that, birds must overcome gravity and drag, and they do this by creating two forces, lift and thrust. Gravity is the force that draws things to the ground. For example, if you let go of something, it falls to the ground. Drag is the force that slows things down. For example, if you put your hand out of the window of a moving car, you can feel drag. Lift is what pushes the bird upwards, away from the ground. Lift overcomes gravity. The aerofoil shape of their wings helps them produce lift.  Thrust is the force that overcomes drag and  pushes the bird forwards through the air. It overcomes drag.

Wing movement is not simply up and down ©Getty Images

Wing movement is not simply up and down ©Getty Images

 

Birds don’t flap their wings straight up and down. When the wing goes upward, the tip moves slightly backwards. When the wing goes downwards, the tip moves forwards slightly and the wing feathers twist slightly. Air passing over the top of the twisted feathers creates a forward push, or thrust.

 

Life Cycle

A lyrebird male dancing to impress a female. His outspread tail is flipped over his head. ©Getty Images

A lyrebird male dancing to impress a female. His outspread tail is flipped over his head. ©Getty Images

Some kinds of birds migrate to other, generally warmer, countries to lay eggs and raise young, and return when the young can take care of themselves. Male birds generally make a display to attract a female. For example, the male peacock opens up his huge tail and vibrates it, and the male frigate bird inflates a red sac on his chest, the male lyrebird dances and sings on a mound of earth. Female birds make nests and lay eggs after mating with a male.

Different kinds of birds make different nests. The fertilised eggs must be kept warm. This is called incubation. Inside the egg, the baby bird develops and grows.

Some newly hatched birds are helpless, like these blackbirds. ©Getty Images

Some newly hatched birds are helpless, like these blackbirds. ©Getty Images

Different kinds of birds take different lengths of time to incubate and be ready to hatch from the egg.

The young have an 'egg tooth' on their beak to help crack the shell and get out of the egg. After this, the egg tooth falls off. The newly hatched chick is exhausted and the downy feathers are wet, but soon dry out.

Chicks stay with their parents until they learn to fend for themselves. This takes a different amount of time for different species.

The eggs of some birds, including chickens, ostriches, ducks, and seagulls, have a bigger yolk and the young hatch ready to move around. The eggs of other birds, including owls, woodpeckers, and most small songbirds, have smaller yolks and the young are more helpless, needing a lot of care from parents in order to survive.

Read more about how birds fly:

https://askabiologist.asu.edu/how-do-birds-fly

Read a chart to help you identify birds you see:

http://www.birdsinbackyards.net/finder

Read kidcyber pages about some bird species:

Read kidcyber pages about birds that do not fly: