22 slides and guide. Most reptiles feel cold to our touch, while mammals and birds often feel warm. But these are subjective and inaccurate evaluations and, as such, are avoided by scientists. The body temperature of poikilotherms is relatively variable, while that of homeotherms is relatively constant. Even more useful terms are ectothermic and endothermic, which suggest two different mechanisms of thermoregulation.
Ectotherms generally obtain heat from their external environment.
Their body temperature varies, corresponding at any time with the temperature of their external environment. Invertebrates, fish, amphibians, and reptiles are generally ectothermic. Endothermic animals, on the other hand, have relatively constant body temperatures. Their body temperature is independent of that of their external environment. Monkeys and walruses, for example, both have body temperatures of about 38 C, despite living in very different habitats.