Answer:
Living birds are diverse (~9,000 species) and they possess some derived characters that are analogous to significant derived characteristics in living mammals (i.e., they evolved independently in birds and mammals). These include upright posture, high metabolic rate/warm bloodedness and large brain size.
Birds evolved not only wings, but many other adaptations that make it possible to fly. Feathers provide insulation, waterproofing, and a lightweight means to become airborne. Birds have honeycombed or hollow bones, reducing body weight.