I've had chickens for about nine years and was confident I had conquered many of the challenges we face raising chickens.
Not being a farm girl, all my chickens are pets and have names, so you know by now we just eat the eggs and I bury any of them who die.
My chicken yard is a fenced off portion of our "mini orchard" with the top open. I never worried about hawks as we only had the Sharp Shins and they never bothered the chickens...until a year ago.
Suddenly we were visited by several Cooper's Hawks and everything changed. I found one of my girls savagely torn apart in the daytime, and before I could cover the entire 90 square yards and five big trees I lost four chickens in three days. It was horrible.
It's curious why the change in environment and what brought the big hawks my pay, but there it is.