My old office has a family of them that return every spring. There would often be four to six of them on the patio outside the cafeteria, spreading their wings and enjoying the sunshine. They like to perch on the roof of the building, because from there they can survey farm fields and a good distance of the road for both directions. They would peck at the reflections in the glass walls and scare the crap out of me when I'd be sitting in there alone. Sounded just like someone knocking on the glass with a ring or hard object!