Animals that keep warm by cells releasing their own heat are called endotherms. This process is called endothermy.

Here are some examples of endothermic animals:

* Mammals: Humans, dogs, cats, whales, bats, etc.

* Birds: Penguins, eagles, parrots, robins, etc.

Endotherms have a higher metabolic rate than ectotherms, which means they burn more calories and generate more heat. This allows them to maintain a stable body temperature regardless of the external environment.