Distinguish between flying birds and flightless birds???

Dear student,

Here are the difference between the two:-
1) Flying birds are smaller in size  than flightless birds. 
2) Wings of flightless birds are poorly developed as compare to flying birds.
3) Tail quills are present in flying birds while it is absent in flightless birds.
4) Flying birds have well developed fight muscles as compare to flightless birds.
5) The copulatory organs are present in flightless birds while, it is absent in flying birds.
   E.g., of Flying birds : Parrot, Crow etc.
   E.g., of Flightless birds : Penguin, Kiwi etc.

Regards