Birds are the only animals that have feathers, which are made of keratin, just like your hair and fingernails. A bird’s wings have the same bones as a human arm, but they are arranged differently. Some of the bones in a bird’s skeleton are hollow. This makes the bird light enough to fly. There are more than 9,800 known types of birds. They range in size from the bee hummingbird (2 ¼ inches long) to the 9-foot-tall ostrich.
All birds:
- Are vertebrates (which means they have a backbone or spine)
- Are endothermic. Also known as “warm-blooded,” endothermic animals regulate their own body temperature which allows them to live in almost every climate on earth.
- Have feathers
- Lay eggs with hard, waterproof shells. The parent birds incubate the eggs until they hatch, and care for their young.
