Warm-Blooded Animals: Definition & Examples

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  • 0:03 Warm Blood
  • 0:48 Warm-Blooded Animals
  • 2:02 Staying Warm
  • 3:02 Staying Cool
  • 4:35 Lesson Summary
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Lesson Transcript
Instructor: Christopher Muscato

Chris has a master's degree in history and teaches at the University of Northern Colorado.

While there are many animals in the world, only a relatively small percentage are warm-blooded. In this lesson, we'll see what defines these animals and which ones are in this category.

Warm Blood

If your temperature is a degree higher than normal, you may start to worry. You may even miss school. If your temperature is a degree cooler than normal, you might worry about that, too. Why are we so concerned over tiny changes in our temperatures? It's because humans are warm-blooded creatures, which means that our bodies try really hard to maintain a constant temperature, regardless of external factors. Biologists call warm-blooded animals endothermic, since heat is generated from within the body. While cold-blooded animals must rely on their environment to control their body temperatures, warm-blooded animals do this naturally. Our bodies can keep us at a constant temperature. This system keeps our bodies warm, and we've got to admit that's pretty cool!

Warm-Blooded Animals

Of all the millions of species of animals in the world, only a relatively small number are warm-blooded. Basically, warm-blooded animals include birds and mammals. There are many birds and mammals in the world, but not nearly as many as there are insects, fish, reptiles, and amphibians. Since birds and mammals are the most recent class of animals, this means that warm-bloodedness is a relatively young adaptation that probably occurred when these animals were evolving.

Now, what was happening around the time that warm-blooded animals evolved? While both mammals and birds likely appeared during the age of the dinosaurs, their evolution really took off after the dinosaurs died. The death of the dinosaurs was soon followed by the beginning of the Ice Age, and being warm-blooded may have been extremely beneficial.

Within a few million years, the tiny mammals had grown into massive mammoths and other Ice Age creatures that dominated the Earth. Since birds are warm-blooded, many scientists also now think that some dinosaurs may have evolved an early system of temperature regulation, especially the group called the theropods, from which birds evolved. Theropods include dinosaurs like T-rex and velociraptor. While this is an exciting idea, it's still a hotly debated topic.

Staying Warm

Warm-blooded animals are defined by their ability to maintain a consistent body temperature, without relying solely on external factors like sunshine or shade. So, how do they (and we) do it? Warm-blooded animals have many ways to keep themselves warm. Birds and mammals both shiver to generate heat through rapid muscle contraction, and many mammals have thick layers of fur or fat to insulate body heat.

The most important system however, and the one that really defines all warm-blooded animals, is the ability to generate heat from the energy in food. All food has energy stored within it, and warm-blooded animals are able to convert the majority of that energy into heat. That's how we maintain a constant body temperature. This does mean that warm-blooded animals have to eat much more food than cold-blooded animals, who only have to eat enough to keep basic body systems functioning. The majority of our food actually goes to heat production, so while crocodiles can eat once a week, we need to eat several times a day.

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