might be a merlin which is about the same size.

But from your picture I bet it's an American Kestrel  

Both are very small but still in the Hawk family. Both are very pretty birds. Kestrel's aren't much bigger than your hand.   

 I've got a few Kestrals around the house. Dang neighbors hit one a few weeks ago with their car. Felt bad about that especially since it is nesting season.