Coopers hawk.
Here's anopther photo of one. http://www.dunbargardens.com/coopers%20hawk%20perched%20on%20barn.JPG
Coopers 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.