Rats are scavengers. Squirrels are not. There.
Depends on what you mean by "scavenger". I've seen a squirrel devour live baby birds - emptied the nest right out while fending off the parent birds' attacks. Like a 3-D horror film, right outside the picture window.
I'd seen predators kill before, but something about that scene with the squirrel was much worse.
Squirrels are just rats with better PR