Endotherm or Ectotherm: warm-blooded or cold-blooded?

Scientists don’t use the terms warm-blooded or cold-blooded anymore when referring to animals.

The terms are endothermic or ectothermic.


Endothermic animals (endotherms) have an almost constantly warm body temperature, no matter how hot or cold the air temperature is. They can control their body temperature by keeping warm or cooling down. They can control the inside heat of their bodies.

In cold weather they can keep warm, and in hot weather they keep cool. Mammals are endotherms. The external covering of fur, hair or wool helps to control their body temperature. Birds are endotherms too.

Endotherms have a body temperature about 36.8 degrees Celsius (98.2 degrees Fahrenheit).

Endotherms control their body temperatures by having fat, fur or thick skin to keep warm and to keep cool they pant, sweat, swim in cool water or lick their fur. Being able to control their body temperature is called homeostasis or thermoregulation.

Humans are endotherms, and that is why doctors take a patient’s temperature. If the temperature is too high or too low, it tells the doctor that the person might be sick, because the inside body temperature is not in the normal temperature range.


a chimpanzee is an endotherm

Great White Pelican

a bird is an endotherm


The body temperature of ectothermic animals (ectotherms) goes up or down depending on the temperature of the air. Their body temperature depends upon the outside heat.

Reptiles are ectotherms. Ectotherms have a cooler body temperature at night when the air temperature is cooler, and a warmer body temperature during the day. Under the sun their bodies absorb heat and become warmer. Ectotherms can slow down their heart rate to almost half the heart rate of humans. To do this, they stop moving to conserve energy. They become lethargic (slow and inactive) in cold temperatures and often they will hibernate (sleep) in winter.

The external covering of ectothermic animals, such as moist skin and wet scales, helps them to adapt to the temperature around them.

African Rock Python

a snake is an ectotherm

Monitor Lizard

a lizard is an ectotherm



Photographer: Martina Nicolls



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