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What Do “Cold Blooded” And “Warm Blooded” Mean?

Scientists dislike using the terms "cold blooded" and "warm blooded."

reptile

Photo: Sjoerd van Oosten (flickr)

Some reptiles are able to match their surroundings temperature but keep their core temperature slightly elevated.

You may have learned the terms “cold blooded” and “warm blooded” in elementary school, but what do they actually mean?

Not So Cold Or Warm…

Most of us learn that insects, fish, reptiles and amphibians are cold blooded because their body temperature changes along with the external temperature, while birds and mammals are warm blooded because they maintain a high body temperature regardless of the external temperature.

But biologists rarely use these terms because they oversimplify the variety of ways animals regulate their temperature.

Ectotherms And Andorthermic

Animals whose body temperature is determined in part by the environment are called “ectotherms.” They can have quite a high body temperature by taking advantage of external conditions, such as basking in the sun to warm up.

Animals, like humans, that control their body temperature internally are called “endothermic.” Endotherms generate heat internally by increasing the rate at which they metabolize fats and sugars.

Animal Examples

Most mammals and birds are endotherms, but did you know that some bees, moths, reptiles and marine fishes are also at least partially endothermic? Partially endothermic organisms, sometimes called “heterotherms” match environmental conditions in their extremities but stay warmer at their core.

On the other hand, some animals typically considered endothermic, like chipmunks, maintain a high body temperature during active periods, but slow their metabolism and drop their body temperature to extremely low levels during inactive periods like hibernation.

Dealing With Changing Temperatures

Animals use many strategies to deal with fluctuating temperatures. At one end of this spectrum are those that are entirely endothermic. At the opposite end of the spectrum are animals whose body temperature rises and falls exclusively with the external environment.

Between these extremes are many different combinations and strategies that allow animals to survive and thrive in many different habitats and conditions.

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