Last time we saw how humans changed New York City from a lush green natural habitat filled with beaver, elk, and other forest critters into a concrete jungle - a human habitat made of roads, buildings, an engineered water system and some seriously excellent pizza. I know I don't have to tell you this, but that's a huge change, and humans make changes like that all over the world. In fact, we change every habitat we touch. But remember what I said before? All living things change their environment. All of them. Don't believe me? Let's take a look at how animals change their environment. 

[Text: Big Question]

Check out this landscape. Something here has been engineered. Can't see it? Look closer at that mound in the middle. That's no ordinary pile of dirt. It's an entrance. It's the front door of a prairie dog burrow. These spaces, like human homes, have been engineered. Engineered by prairie dogs, and these burrows are seriously well designed. Prairie dogs dig burrows to suit their needs. They don't just dig at random, they make a home that does what they need it to do for them to survive. To start, they need their burrow to be pretty deep. The entrance to the burrow goes about 1 to 3 meters down and then becomes a horizontal tunnel from 3 to 5 meters long. The burrow also has a number of side chambers lined with grass for storage and for sleeping. They even have a little chamber to use as a bathroom, which I guess good for them. But to build the burrow, these industrious prairie dogs have to move dirt, which changes their environment. The ground wasn't full of tunnels before the prairie dogs came to town.

Or take a look at these termites. Termites build homes that can be over 3 meters tall, built from the chewed remnants of wood, mud, and even poo. These termite mounds are an example of an animal building a home, adding to their environment, as opposed to removing matter to create space like the prairie dogs did. Some animals change the environment without meaning to. Squirrels love nuts, but not in the same way I love pizza, and I mean that because I never forget where I set down my slice, but gray squirrels bury a lot of nuts and then they lose track of many of them. Those forgotten buried nuts are left alone and become trees, so without meaning to, gray squirrels change the environment by planting new trees. I know what you're thinking, okay these are changes sure, but they aren't on the scale that humans did to New York. Well, hold up, I've got something to show you.

[Text: Investigation]

Beavers! Remember those beavers that lived in New York? Those guys were changing things too. Beavers are like little furry engineers. How cute is that! Beavers make major changes to their environment. First, beavers are little lumberjacks. They gnaw on trees until only a thin sliver of the trunk is left and then they wait for the wind to knock it down. By selecting which trees to take down, they're changing the forest, altering which trees go where and making less space for the animals that used to live in those trees. They're also making more space for new trees to grow, and then they build their famous dams. The beavers use rocks, logs, branches, and mud to slow down the flow of a stream. Then they build dome-shaped homes in the center of the pond out of branches and mud, usually they can only be reached by underwater entrances. When they're done, beaver dams create a pool of water, turning what was once field and forest into wetland. By damming a river, beavers build an entirely new habitat for other animals. Now fish and amphibians can move into a space where squirrels once roamed, and it changes other aspects of the water too. Stream ecosystems are different from pond ecosystems, because different animals and plants flourish in still water rather than in flowing water. So, the beavers have totally altered their environment, creating an entirely different ecosystem than what used to exist. That's a whole lot of change. 

[Text: Conclusion]

So the beavers build the habitat that suits their needs - they build homes for themselves, and in doing that, they change the environment around them. Does that sound like any other creature you know? Yes. Humans change their environment in big ways, but we can't forget that's the nature of, well, nature! Humans are just as much a part of the natural world as all of the other plants, animals, and other living things on Earth. You and me and the prairie dogs, termites, squirrels and beavers were all on this planet together, changing everything we touch. But New York Style pizza? That's strictly the work of humans.