Birds and mammals, including human beings, are warm-blooded animals. Nearly all other kinds of animals are cold-blooded.
Scientists refer to warm-blooded animals as endothermic or homeothermic.
The body of a warm-blooded animal produces heat by burning food. Shivering and physical activity also generate body heat. A layer of fat beneath the skin, plus a covering of hair, fur, or feathers, helps keep a warm-blooded animal warm. The animal's body can also conserve heat by reducing the flow of blood to the limbs and to uncovered skin. The body becomes cooler by such means as panting and sweating.