[gamin]

Jeff is correct about the diseases rats carry and their need to gnaw on anything handy to keep their lower incisors worn down. I would add that they are nasty critters. They have no control of their bodily functions. They pee and poop almost constantly. You can see the poop easily. You need a good UV flashlight to see the urine trails. Lights out of course. I am not fond of invisible rodent piss all over my house or garage. Rats have no redeeming value except as lab animals.
Rats living high up as in trees are roof (black) rats. Slender and very agile.
Rats living in burrows at ground level are norway rats. Larger than roof rats and lighter in color.