I am not a biologist, so all I am able to tell you is from my basic knowledge and what I have learned over the years. Birds are not the only animals to fly.
Bats also have the ability to fly, although their body's are very different.
Well, it's the bodies covering of feathers which no other creature has which makes it unique. Feathers have a central shaft with a vane or web on either side. They are made of a strong, flexible material called keratin, which also forms human hair and nails. There are three main types of feather, flight, body and down. These grow out of follicles in the skin.