Write down an answer and see how it compares to my 6 attributes birds. Most birds fly, but flight is not exclusive. Can you list the 4 groups of animals that are capable of TRUE FLIGHT? (Hint: gliders don't count.) See answer at the end of this post. Bats also fly but birds are far more modified for flight than bats. Indeed, because of flight and the modifications to it (the aerodynamic demands of flight), birds are remarkably similar. There is far less difference between an albatross and a hummingbird than an elephant and a shrew or monkey.
TO RECAPITULATE:A bird is a flying vertebrate with feathers. (Cursorial birds (= ratites) are believed to have evolved from flying ancestor.)
Answer to question above--This is kind of a trick question, since one group is extinct.
1. Birds 2. Bats 3. Insects 4. Pterosaurs