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

Explanation

So many modifications are observed in birds that help them in flight.
1. Exo and endo skeletons and body structure features might have contributed for their successful arieal mode of life.
2. Exoskeleton consists of epidermal feathers. Feathers are unique to birds. They are useful for flight, particularly the Quill feathers help in flight.
3. Body is boat-shaped and streamlined.
4. Fourlimbs are modified into wings.
5. Many bones are neumatic with extensions of air sacs.
6. All modern flying birds are provided with powerfull breast muscles (flight muscles) chiefly the pectoralis major and pectoralis minor.
7. Lungs are associated with air scas.