Cold-Blooded and Hot-Blooded Animals

Why are some animals called cold-blooded? What’s hot-blooded? Why do these exist and what do they mean for the animals? The whole thing is about different highs and extreme lows in temperature. Let’s start from the beginning:

Cold-blooded animals

  • have a changing body temperature (depends on their surroundings)
  • are fish, amphibians, reptiles, insects and invertebrates

Hot-blooded animals

  • always have the same body temperature (unless they’re sick)
  • are mammals and birds

Cold-Blooded and Hot-Blooded Animals Cold-Blooded and Hot-Blooded Animals - Photo: Dirk Ercken/Shutterstock

The difference between hot-blood and cold-blooded at a glance:

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 Cold-bloodedHot-blooded
Body temperature Dependent Independent
Feathers/fur No Yes
Need to feed Irregular, low Regular, high
Metabolism Low High
In heat Look for shade/cool Sweat
In cold Look for heat/sun Shiver
In winter Not active Active

1. Hot-Blooded Animals

(= mammals, birds)

How do hot-blooded animals maintain their body temperatures?

It takes a lot of energy to keep their body temperatures the same all the time. How these animals get or save this energy:

Arctic Fox Arctic Fox - Photo: outdoorsman/Shutterstock

• Feeding

Hot-blooded animals get energy from their food. A large portion of this is used to control body temperature. They have to eat more often than cold-blooded animals. Example: if you haven’t eaten for a long time, you might notice that you start to get cold and shiver. When you eat something, you get warmer.

• Feathers, fur and fat

Hot-blooded animals almost all have fur, feathers or a thick layer of fat. Some animals even get a thicker coat in winter, called their winter coat. It starts to grow when it gets colder outside and is shed again in spring. Dog owners will know all about this, as there will be much more hair lying around in shedding season.

Birds keep warm with their fluffy down. These feathers are so cozy and warm that they’re often used in winter coats. Marine mammals like whales have a thick layer of blubber to protect them from the cold.

Blue Tit Blue Tit - Photo: jausa/Shutterstock

What if it gets too hot for hot-blooded animals?

They sweat! Each animal does this in its own way. Dogs sweat using their tongues (panting). Elephants pump blood into their big, flat ears and flap them around.

2. Cold-Blooded Animals

(= fish, amphibians, reptiles, insects and invertebrates)

Cold-blooded animals cannot control their own body temperatures. They adapt to the temperature of their surroundings. When it’s very cold outside, their body temperature decreases. When it’s very warm, it increases.

These animals aren’t very active in the cold, as it would take up too much energy. They need energy from the sun in the form of heat. That’s why you can see reptiles and amphibians basking on rocks to actively increase their body temperature. If they get too hot, they withdraw to a cave.

Cold-Blooded and Hot-Blooded Animals Cold-Blooded and Hot-Blooded Animals - Photo: Dirk Ercken (frog), Tatyana Vyc (dog)/Shutterstock

In winter, cold-blooded animals hibernate. They breathe very slowly, have a very low heart rate and don’t eat anything. In spring, the animals can move again. This type of hibernation is called brumation. The wood frog is especially impervious to cold. It can survive in 21.2 degrees Fahrenheit (-6 degrees Celsius)!

Did You Know?

Not every hot-blooded animal has the same body temperature. Humans are 98.6 degrees Fahrenheit (37 degrees Celsius), horses 100.4 degrees Fahrenheit (38 degrees Celsius), dogs 102.2 degrees Fahrenheit (39 degrees Celsius) and birds 107.6 degrees Fahrenheit (42 degrees Celsius).

Cold-Blooded and Hot-Blooded Animals Cold-Blooded and Hot-Blooded Animals - Photo: Ondrey Prosicky (frog), Tatyana Vyc (dog)/Shutterstock