What are three distinguishing characteristics of birds?

1. Feathers: Birds are the only animals that have feathers. Feathers are made of keratin, the same protein that makes up human hair and fingernails. Feathers are lightweight and strong, and they help birds fly and stay warm.

2. Beaks: Birds have beaks instead of teeth. Beaks are made of keratin, and they come in a variety of shapes and sizes depending on the bird's diet. Beaks are used for eating, drinking, preening, and defending themselves.

3. Wings: Birds have wings that allow them to fly. Wings are made up of bones, muscles, and feathers. Birds are the only animals that can fly, although some other animals, such as bats and flying squirrels, can glide.