A homeotherm is an animal that keeps its internal body temperature constant, usually within a restricted temperature range.
The mammal is also a homeotherm ,because it keeps its internal body temperature within a relatively restricted range.
Through metabolic activity like shivering and perspiration, they manage to keep their internal body temperatures constant despite the influence of changing ambient conditions.
Homeotherms include birds and mammals.
Poikilotherms:
Poikilotherms, also known as cold blooded animals, are animals that make use of external sources of heat to regulate their internal temperature.
Poikilothermic creatures, such as fish, amphibians, and reptiles, as well as birds and mammals, lower their metabolism and body temperature during hibernation.