Question

how birds fly up in air?

Answer 1

you could visit this site to get the mechanics of bird flight
http://www.n6iap.com/ornithopter/howbirdsfly.html

besides
birds have streamlined body
they have light hollow bones so their body weight is less
strong chest muscles
high metabolic rate to provide energy quickly and continuously

hope this helps :))

Answer 2

Birds are able to fly because of a variety of specialized adaptations. They have high metabolisms to supply their body with energy. They have lightweight bones. They have feathers, some of which are "flight feathers" that are long, strong, and able to produce lift and act as control surfaces. They also have a bone called the furcula, more commonly known as the "wishbone," in their chest, which is very important for being able to produce the strength and skeletal support needed to flap their wings.
The mechanics of flight are not unlike an airplane; the factors of lift, weight, thrust, and drag all interact to allow for controlled flight. By flapping their wings, birds create thrust and lift. They are able to steer by changing the shape and orientation of their wings and tail. They change the shape of their wing between the upstroke and downstroke as they flap to minimize drag on the upstroke and maximize the thrust generated downard on the downstroke, providing both lift and thrust.

Answer 3

Characteristics of birds:
Light weight.
Pneumatic(air) bones.
Specialized muscles
Specialized lungs.
Streamlined body and wings.
High metabolic rate.(no food waste is retained, they are fast metabolized to produce energy and waste is excreted)

Answer 4

The same way they fly down in the air. Read Jonathan Livingston Seagull.