Birds are amazing creations by the nature. The most important feature that makes the class of animals unique is their ability to fly. The forelimbs of the birds are formed to be wings that help them to fly. Along with their wings, various other anatomical features help them to adapt for the action of flight. Such anatomical features include their lightweight bones, presence of feathers, and many more. Flight is the primary form of locomotion generally observed in birds.
The elementary mechanism of a bird flight consists of four primary actions: lifting, gliding, flapping and dragging. The lifting force is being produced when air flows on the wings. This in technically termed as airfoil. The shape of the airfoil determines the actual upward force that can be provided on the wings, when the air movement has been directed downwards. The second action, gliding happens when both vertical and forward force are obtained from the wings. It is possible since lift force can be generated perpendicularly to that of the airflow.
Flapping is an important action in bird flight. The flapping enables not only to help in lifting but also provides a thrust that enables to counter the weight as well as increase the speed. This feature in bird flight helps to climb up and maintain the height. The two basic movements in flapping include the stroke-up and stroke-down. Both these movements ensure the required thrust in flight. Dragging is the feature that reduces the efficiency of flight especially because of the hindrances like friction and counter pressure.