They are warm-blooded, which means their body temperature is constant. They are the only animals to produce milk, and only mammals possess true hair or fur. Most birds can fly. They have streamlined, feathered bodies and wings. Their legs and feet are scaly and they have beaks for feeding, but no teeth.
Birds are warm-blooded and their young hatch out from eggs.
Amphibians are born in water and live the early part of their life there. Later they move to land. Fishes are cold-blooded and live in water. They start life as eggs. They have scaly skins, and fins help them to swim.