Reptiles and Amphibians

Reptiles and amphibians are both cold-blooded, which means they cannot make their own body heat the way mammals and birds do. Instead, their body temperature rises and falls with their surroundings. This is why, on a cold morning, you might see a lizard lying flat on a sunny rock — it is basking to warm its body up before it has the energy to move quickly and hunt.

Being cold-blooded has a big advantage: these animals need far less food than warm-blooded animals of the same size, because they do not burn energy keeping warm. A crocodile can survive for months between large meals. The downside is that when it is cold they become slow and sleepy, so many reptiles and amphibians live in warm places or hide away during winter.

Amphibians — frogs, toads, newts, and salamanders — have moist, smooth skin and usually need to live near water. The word amphibian means "two lives", because most begin life in water as gilled young (like tadpoles) and later change shape to live on land as air-breathing adults. Many amphibians can even breathe partly through their damp skin, which is why it must always stay moist.