I published Duluth naturalist’s David Benson’s Owls of the North a few years ago…Great little book, if you haven’t seen it. Fascinating info on all our northern owls…including the Northern Hawk Owl. Here is an excerpt about Hawk Owl hunting:
Hawk Owls hunt from a convenient perch, searching for prey by sight and then swooping quickly down for the kill. They will chase prey short distances, and sometimes they hunt from perch to perch, dropping down for prey and then swinging up to a nearby perch if they fail to catch their target. Hawk Owls have also been seen hovering over potential prey—unusual behavior for an owl [see photos this post—Sparky]
Alone among owls, Hawk Owls have a falcon-like notch in their bill to sever the spinal cords of their prey. Owl species often use their bills in a similar way, and presumably the notch helps the Hawk Owl to do this with more efficiency.
Congruent with their daytime activity, Hawk Owls rely on sight more than hearing for hunting. Their ears are symmetrical, so they apparently do not need the kind of precision hearing used by most other owls. When scanning for prey, Hawk Owls lean forward almost to the horizontal and pump their tails (a most “un-owly” posture). When they strike, their drop off the perch can look almost like and accidental fall until they begin to glide to the kill.
—from Owls of the North by David Benson (Stone Ridge Press, 2008, ISBN-978-0-9760313-4-5)