endothermy
Both mammals and birds evolved endothermy. Endothermy means controlling body temperature within a narrow range from the inside through biochemical or physical means. For example, on a cold day, an endotherm may produce more body heat by increasing its rate of metabolism. On a hot day, it may give off more heat by increasing blood flow to the surface of the body. That way, some of the heat can radiate into the air from the bodys surface. Endothermy requires more energy and food than ectothermy. However, it allows the animal to stay active regardless of the temperature outside. You can learn more about how vertebrates regulate their temperature by watching this video: https://www. youtube. com/watch?v=TSUCdLkI474 .