One of the most notable things about animals is their ability to move from one location to another, what scientists refer to as locomotion. As the animals in this video segment demonstrate, there are many ways to get around. For example, some animals, including iguanas, cheetahs, and chimps, use legs or other appendages to push or pull them in the direction they want to go. Other creatures, including snakes, earthworms, and many single-celled organisms, have no legs or arms to propel them and instead move by transforming the shape of their bodies to slither or squeeze themselves across the ground or through soil or water.

Scientists sometimes describe different forms of locomotion based on the type of habitat in which they occur. Animals like the dolphin, ray, and scallop from the video, which spend most of their time underwater, use aquatic forms of locomotion. Burrowing rodents, earthworms, snakes, and other creatures that spend much of their time underground use fossorial locomotion. Animals that spend most of their time walking, running, or hopping along the surface of the earth use terrestrial forms of locomotion. Lastly, animals that move around above ground, either in trees or in the air, are said to use arboreal or aerial forms of locomotion.

So what's the reason for all this moving around from place to place? Not all animals do it. Barnacles, for example, do just fine permanently attached to rocks and piers along ocean shores. That's because the barnacle has access to everything it needs in one place. All animals require at least three things to survive: food, water, and shelter. In the barnacle's case, the ocean tides provide a regular supply of water and nutrients. And a barnacle provides its own protection: a hard shell with very sharp edges. In most habitats, however, it is quite common for an animal's food, water, and shelter to be in different locations. Animals that live in these habitats must travel, sometimes great distances, sometimes constantly, to find the resources they need to survive.