Hawk Owls like all owls swallow their prey whole or large pieces of prey depending on what they catch. They are unable to digest bones or hair/fur…over a period these undigested parts are formed into an oval shape pellet then regurgitated or coughed up. Similar to cats coughing up a hairball…you get the idea.
My best guesstimate for the pellet size would be 2+ ins. long…only because I didn’t go to search for it.
From my observations over the years…after a pellet is coughed up its an indication the owl is hungry again and will be actively hunting.
I just happened to be in the right location at the right time.