The main characteristic of the flying mammals is that they are all species of bats. Bats are the only flying mammal. Some of the characteristics of bats are that they fly almost exclusively at night, they can't walk very well, and they have excellent hearing.
Hollow bones, feathers, and there wings. Just a few.
Cute question! Birds like to get high. Feathers allow birds to fly.
Flightless birds have a small keel and wings.
reproduce
Wings, feathers, and light bones.
Their bones are hollow which makes the bird light. With its lightness it is able to fly.
hollow bones and feathers help
Soft, downy feathers keep birds' bodies toasty and warm. At the same time, the waxy outer ones keep off the rain. More importantly, feathers allow birds to fly. Birds beat their feathered wings to lift off the ground and fly through the air.
It is not only birds that fly. Bats fly and they are not birds.
Ducks fly, lay eggs, have feathers, molt, migrate - all of which are bird characteristics.
They have bones in their wings that allow them to fly, if they did not have bones, they would be a lump of skin and organs.
Contour feathers. Wait: I was wrong. The answer is remiges.
Just because penguins, ostriches, emus and kiwis don't fly doesn't automatically make them not birds. They still have the same characteristics that make them birds like all other birds have: a beak, feathers, porous bones, etc. The ability to fly is not part of the definition of what makes a bird.