Fish, reptiles and amphibians are ectotherms and use their surroundings to warm their bodies. Ectotherms that live in water do not need thermoregulation because the high specific heat capacity of water means that the temperature of water does not vary much. Ectotherms that live on land experience a wide variation of temperatures.Mammals and birds are endotherms and can maintain a fairly stable core body temperature in most environments. They use metabolic processes to produce heat and active cooling processes in hot conditions. They also have behavioural and physiological adaptations for hot or cold climates. The ability to maintain the core body temperature within a narrow range means that they need to consume more food than ectotherms of a similar size.