I remember an author (who? Maybe Barbara Holland in "Secrets of the Cat," an animal book I was obsessed with as a preteen) saying that a hawk had once swooped by her feeder and it was as if his wings had left a stain on the air -- all her usual clientele stayed away for days.

Should have figured you'd have experience with at least a few of these raptors. What's the context where you see sparrowhawks most often?