There are actually two major types of rats, Norway rats, and Roof rats. The Roof rats are sometimes called tree rats. They climb well, and usually have their nests off the ground. The Norway rats burrow into the ground and, while they will climb, they don't climb nearly as well as roof rats. The two species do not get along well, and don't interbreed. Either species is very destructive, and they do billions of $ of damage each year.
I have a neighbor who has stacks of junk and lots of spoiled food around. His rats come over here, and I am giving them all the poison they want, but since he has mega sources of food for them, the poison thing isn't working well. Guess I'll have to get some traps.