Coopers hawk.
Here's anopther photo of one.
http://www.dunbargardens.com/coopers%20hawk%20perched%20on%20barn.JPGCoopers hawks and Goshawks get my full grown mallard ducks on occasion when the ducks are in the woods roaming outside of their pen. Similar birds are sharp shinned hawks and goshawks.
But i'd bet money you have a hungry Coopers hawk and he knows there food there as he's returning.
Sometimes they are temporary visitors to feeders, sometimes they return, sometimes they are migrtating through. They are everywhere, from cities to parks to dense woods and shorelines.
Thanks , Its funny I have these pigion like birds that are hanging around also. Grey body,blackish grey feathers on the wing, yellow feet yellow beak. And on the back of the head the have a crown like band of white feathers.
After the first kill I was convienced that the pigion like bird was the culprit. I called around and discribed the bird. No luck, then the other day when the hawk came back I was so excited. I was going to take a picture of the chicken killing pigion. I was suprised when it turned out to be a actual hawk like bird.

So last night I saw the pigion. Not sure if it really a pigion. Its not the same as the city pigions. A bit larger and pretty smart.
Jason