See the Difference

Have you ever held a lizard, a snake, or a turtle? Its body temperature is likely lower than yours. You couldn’t tell that just by looking. You probably wouldn’t be able to feel a difference, either. But you can see the difference in thermal infrared images. They show how cool or warm an object is by measuring the amount of heat it gives off. 





By fanning its ears, this elephant begins to cool down.

This spider’s body is cooler than its environment.

Look at the thermal image below of someone holding a lizard. The bright red of the person’s hand shows a warm, steady body temperature. This is true even though the surrounding air is cooler.

The lizard shows up mostly as shades of blue. Before being held, it appeared as dark blue, like the background. No surprise there! The lizard’s body temperature was the same as the temperature of the surrounding air.

But what happens as the reptile and mammal touch? The reptile absorbs heat from the person’s hand. Its body is warming. Its feet and legs show up as green and yellow. What will happen if the person continues to hold it?



This cat generates its own body heat.
It leaves behind a trail of warm pawprints.

Watch as a person leaves
warm footprints on a cold floor.




This gharial soaks up the sun’s rays. Then its body temperature rises. 

Chemical reactions from food also provide energy. And energy produces heat. In this way, an animal’s body is like a furnace. But instead of burning natural gas, the body “burns” food.

The faster an animal’s metabolism, the more energy the animal has for keeping warm. Which animals do you think have the faster metabolism?

A Living Furnace

Why can some animals keep the same internal temperature while others cannot? The answer is metabolism.

An animal’s metabolism is all of the chemical reactions that take place in its body. Tiny molecules are constantly combining and breaking apart in body cells. They form new substances. Most of these chemical reactions occur as food breaks down.

Food provides the materials to grow. It also repairs damaged cells. If you cut your finger, new cells grow out from either side of the cut and heal it. The new cells come from the food you eat.




These meerkats don’t need to wait for the sun. They control their own body heat and are already warm. 




Some of these flamingos have one leg that is hotter than the other.  When a flamingo stands on one leg, that leg loses heat, while the other leg is tucked up next to its body keeping warm. 

You guessed it—endotherms. The metabolism of birds and mammals is fast enough to produce constant warmth. This allows the animals to maintain a high body temperature. Birds have the fastest metabolism and the highest body temperature, 40oC to 42oC (104oF to 108oF).

Can you think of a reason birds need such a fast metabolism? Think about how birds move. The high rate of metabolism produces the energy birds need to fly.