Birds, page 2

Birds (page 2)
Covering

All birds are covered with feathers. No other animal has feathers. The feathers of some birds are brightly coloured. Generally male birds are more colourful than 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 regularly, generally once or twice a year. Each is replaced with a strong new feather. This process is called 'moulting'.

The largest and most important are contour feathers, which give a bird its shape and colour, and provide protection against the weather. They include the the flight feathers on the wings and tail. They have strong shafts and side branches called barbs. The barbs are lined with tiny hooks called barbules, which keep the barbs together.

Barbs are branches from the shaft linked together by barbules
photograph © [2008] Jupiterimages Corporation

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 acts as insulation: they keep a bird from getting too hot or too cold.

The other kinds of feathers are Semiplumes, Filoplumes, Bristles and Powder feathers:
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.

How do Birds Fly?
It is not the flapping of wings that makes a bird fly – there are times when a bird glides without moving its wings. It is the shape of a bird’s wing that helps it fly. The shape 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.

photograph © [2008] Jupiterimages Corporation

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.

In order to fly, birds must overcome gravity and drag. They do this by creating two forces, lift and thrust.

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. 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.

Reproduction and Life Cycle

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.

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.

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.

Some kinds of birds migrate to warmer countries to lay eggs and raise young, and return when the young can take care of themselves.

The earliest bird was an Archaeopteryx, which lived about 150 million years ago. It was the size of a raven, was covered with feathers, and had wings.	The most yolks ever found in a single chicken's egg is nine.
The smallest bird is the Bee Hummingbird (5 cm), and its eggs are the smallest bird eggs.	The largest bird is the Ostrich (2.7 m), and it lays the largest eggs.To hard-boil an ostrich egg takes 2 hours.
The elephant bird of Madagascar, which is extinct, laid an egg that weighed over 12 kilos.	A bird's heart beats 400 times per minute while resting and up to 1000 beats per minute while flying.
The eggs of the Royal Albatross take 79 days to hatch.	Pigeons can reach speeds up to 160 kilometres per hour. Swifts, doves, falcons, and sandpipers can reach speeds of around 320 kilometres per hour.
A bird's body temperature is usually a few degrees warmer than a human's. As birds can’t sweat, about three quarters of the air they breathe is used to cool their bodies.	A homing pigeon called Cher Ami lost an eye and a leg while carrying a message in World War I. Cher Ami won the Distinguished Service Cross. Its leg was replaced with a wooden leg.
The only known poisonous bird in the world is the hooded pitohui of Papua, New Guinea. The poison is found in its skin and feathers	The American turkey vulture helps engineers find cracked or broken underground fuel pipes. The birds gather where there is leaking fuel because it smells like rotting meat, which is vulture food.