How streamlined help the bird and airplane to fly?

In flight the engine thrust must overcome the air resistance, or drag. Drag depends on frontal area (for example, large, airliner; small, fighter plane) and shape (drag coefficient); in level flight, drag equals thrust. The drag is reduced by streamlining the plane, resulting in higher speed and reduced fuel consumption for a given power. Less fuel need be carried for a given distance of travel, so a larger payload (cargo or passengers) can be carried.