Structural details of Birds.

As a group of animals, birds have evolved in various range of body sizes. The smallest bird is the Bee-Humming bird which weighs only 1.6g and is smaller than many butterflies and moths in the rainforest. Whereas the largest bird is the North African Ostrich which weigh up to 125kg. Between these two extremes are the majority of earth's birds-an enormous variety of species which have managed to colonize habitats as diverse as polar ice, and tropical rainforest.

1.Bee-Humming Bird (Up) 2. North African Ostrich(Down)

The Outer surface: A bird's entire body except its beak and feet, is usually covered with feathers. Some birds, like vultures have bare heads and necks.

Outer diagram of a bird

The Digestive system: Because birds don't have teeth, the digestive system has to carry out all stages of food breakdown. I birds that eat plant matter, the gizzard grinds the food into pulp. The Gizzard is a muscular bag that grinds up food, often with the help of stones that the bird swallows.

Breathing: Up to a fifth of a bird's body volume is taken up by air sacs which are connected to lungs. The air sacs even extend

Inner diagram of a bird

Light weight helps birds to fly : Bone is a heavy material. For land animals, its weight does not create much problems as up to a point more muscles can always be added to move it. Whereas, birds have to work within a strict limit of weight if they have to be able to fly and they do this by using a lightweight skeleton. The long bones of flying birds are hollow and are reinforced with lightweight internal struts. This allows the bird to make all important savings in weight. For example the skeleton of a pigeon weighs just one twentieth of its whole body. In many flightless birds and diving birds the bones are solid.