Trees protect chickens from predators

I was watching our Light Sussex chicks forage in the garden when...out of the blue...a hawk swooped down on top of them.  Chicks scattered everywhere, I screamed in anguish, our scaredy cat ran for cover --- quite the excitement for our quiet little farm.  I think the combo was just too much for the Sharp-shinned (or was it a Cooper's?) Hawk because he missed his prey and flew on down the powerline cut and out of sight.

Except for losing chicks to rats, we've never had any trouble with predators on our farm.  I've always given credit to our well-trained dog, who patrols the perimeter day and night, but I think I should also consider the fact that forest pastures have more going for them than whatever food the trees produce.  Those trees shield our flock from avian predators.  Our open garden is much more like a traditional pasture, with no cover for the chicks to hide in and no canopy to shield our tasty morsels from birds of prey soaring overhead.  Small wonder that our near miss occurred when the chicks got bold enough to try out this open habitat.

I wrote previously that chickens are much more likely to go out on pasture if trees and bushes are present, and I can't say I blame them.  I wonder if the reason our laying flock refused to forage in the oat and pea pasture was because it was suddenly a wide open expanse with no tall weeds to protect them?  Yet another data point to add to the mix as I design the optimal chicken playground.