2. I’ve never personally seen crows roosting to be a “bad omen” or some kind of sinister action; I don’t get many large. Roosts around where I live, so judging from the few large gatherings I’ve seen, they give the impression of a spectacle of nature.
4. I’d argue that some of the American Crows predators might benefit from large amounts of crows. For instance, if a large amount of crows have been in an area, there would be many remnants of their flock. Clues like droppings, feathers and, if in a human-populated area, trash. Could lead a crow predator to either wait around the area to see if they’ll return or track them down to score a potential meal.