What are the modifications that are observed in birds, that help them fly?

Explanation

The following modifications helps birds to fly: -
(1) Presence of feathers.
(2) Presence of pneumatic bones : Pneumatic bones are long hollow bones with air cavitie.
(3) Fore limbs are modified into wings to help in flight.
(4) Hind limbs generally have scales helping them to clasp the prey in - flight or a tree branch.
(5) Excretion of uric acid , and faeces is through a single opening, and excretion uses very.little amount of water, to reduce body weight.
(6) Aerodynamically built body helps in flying ( by reducing friction).