We've had a few hawks visiting our property for the last week. It's stepping up our chicken tractor plans, but it was so nice free ranging while the hawks seemed to not notice us! We had a murder of crows roosting nearby all winter, but they seem to have moved on now that it is spring.
The hawks come in pairs, circle over where our chickens hang out and move on. I wish I were confident in knowing what exactly they're after. It seems that if they were serious, they'd have made a kill by now. We have chicks in a large pen, which is mostly where they circle, but they can't get in there, nor have they tried. 
When the children see them, they run toward the hen house, cawing like crows. Apparently, the pullets pay attention to the sky, at least. Any time the hawks are around, the pullets aren't to be found. But I can't help but think the hawks have to know where they are. We have four hens, too, but they are warier all around, staying under cover most of the day. The pullets hang around the barns and hen house, but are much more willing to forage out in the open.
The only thing that has swooped down was a kestrel, but it was half the size of the chickens. It almost flew into me as I was coming around the corner of the barn, or I'd have never known it was there!