Cooper's or Sharp-shinned Hawk Revisited

Sharp-shinned Hawk kills an American Goldfinch

It was another snowy day in the coulees today.  I was sitting at the kitchen table eating a late lunch when I heard the boom of birds bouncing off my kitchen windows.   

No birds were injured by the plate glass, but I spotted a male American Goldfinch dead on the ground, victim of the other predator in my yard.  An accipiter was staning over the body.

I knew it was an immature (brown plumage and yellow eye), but which one?  A Cooper's Hawk or a Sharp-shinned? 

Sharp-shinned Hawks have heavy streaking on the breast;  Cooper's have light streaking.  What's "light?"  What's "heavy?"

I see so few of them, I wasn't sure.  So I went to my bookshelf and pulled out the Photographic Guide to North American Raptors. 

The photo on page 34 showed a juvenile Sharp-shin with "streaking on underparts extends onto belly."  The Cooper's photo on page 37 showed "fine dark streaking ... sparse on the belly."

No question:  it's a Sharp-shinned Hawk.

I wonder how many birds that Sharp-shinned Hawk needs to eat on a snowy winter day...