What flight adaptations are present in birds?

What flight adaptations are present in birds?
Or
What are the modifications observed in birds that help them to fly?

Flight adaptations found in birds
(i) Body is streamlined to reduce air resistance during flight.
(ii) Four limbs are modified into wings.
(iii) Wings have long quill feathers to increase the efficiency of heating of wings,
(iv) Pneumatic bones are present to reduce the body weight.
(v) High metabolic rate to provide energy.
(vi) Air sacs present in lungs help in double respiration.