We were at the Grand Canyon a month ago and the ravens keep a close eye on Everything that goes on in the canyon area including the Colorado river. They are just trying to make a living and are smart and aggressive enough to have figured it out that people= easy food.
Some people actually feed them but most just leave food items unattended so the birds who fly over the area constantly, know exactly when there is opportunity for winged robbery.
When I dropped my pack at Tanner beach and went for a walk for ten minutes, my top pouch that had a closed zipper with a cord on it had been opened and a plastic zip lock with some small electronics was on the ground with chew holes in it. I did not remember leaving the zipper open and though initially that a furry ground animal had pulled the bag out but when it happen a second time after leaving the pack hung in a tree after a days walk to the Little Colorado, I knew that the local raven who was always present, was the thief.
He owned that area. As someone has already said, they are the raccoons of the sky.
Dave