It stops and swings its head. It sticks out its chin. It twitches its tail. Suddenly, the lizard liſt s up its right front


A


foot and its leſt back foot. It holds them above the sand for a few seconds. T en it quickly switches feet. T e lizard looks like it’s dancing. It’s not. It’s


trying to stay cool. Heat moves from the hot sand into the lizard’s feet. T at heats the lizard’s whole body. Each time the lizard liſt s its feet, they cool down. Its body does, too. Soon, the desert gets even hotter. Now even


the lizard’s fancy footwork doesn’t help. So it dives headfirst into a sand dune. It digs with its shovel-shape nose. It paddles with its legs, pulling its way to deeper sand. T e sun’s heat doesn’t reach this deep, so


this sand isn’t as hot. It’s as much as 28° Celsius (50° Fahrenheit) cooler than the sand on the surface. T e lizard rests and cools down.


Heat Danger Keeping cool is important. When an animal gets too hot, its body temperature rises. Bad things can happen then. Too much heat can cause the brain and


other internal organs to swell. When that happens, these body parts can stop working. So if the animal can’t lower its temperature, it will die. For a cold-blooded animal like the lizard,


survival means finding the right place. It uses its environment to control its body temperature. Here’s how it works. If the lizard is cold, it slowly crawls to a


sunny spot. It soaks in the heat. Its body warms up. Now that its muscles are warm, it can zip quickly over the sand. It can pounce on insects. T en, when the lizard gets too hot, it gets out of the sun. Its body cools down. In a day, the lizard’s temperature rises and


falls. It can survive as long as it doesn’t get too hot or too cold.


4 NATIONAL GEOGRAPHIC EXPLORER


lizard skitters across hot desert sand.


Self Control Like the lizard, amphibians, fish, insects, and reptiles are all cold-blooded animals. Mammals and birds are warm-blooded animals. A warm-blooded animal doesn’t use the


sun or shade to stay the right temperature. It uses food. Energy from food helps keep the temperature inside its body just right. It always stays about the same, even if it’s really hot or cold out. Warm-blooded and cold-blooded animals


have something in common, though. When it’s hot out, they all need ways to beat the heat. Some animals use a special body part. T is


physical adaptation lets heat escape from their bodies. So they cool down. Other animals act in ways that help keep


them cool. Behavioral adaptations can be as odd as the lizard liſt ing its feet. T ey also can be as simple as finding shade or a cool pool.


Fast Fact: An animal can cool down 25 times faster in water than in air.


Splish, Splash A flamingo spends a lot of time in the water. You can oſt en find it standing on one leg in shallow water. Usually, that’s enough to keep this pink bird from getting too hot. Sometimes, though, it’s not. T en the bird puts its second leg in the water. Now more of the bird’s bare skin is under


the water. T e liquid gently laps against both legs. As it does, heat inside the fl amingo’s body escapes into the water. T at’s because heat naturally moves from warmer places to cooler places. T e bird cools down. A hippopotamus takes its splash time to


extremes. It lives in Africa where temperatures can soar up to 40°C (104°F). A hippo may spend up to 16 hours a day in the water to beat the heat.


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