Living with wildlife (and chickens)

I woke up this morning hearing a ruckus from the chickens. I looked out the window and saw the rooster, out of his pen, running for the bushes near the house. I got dressed and went out to see what was up and startled a mature bald eagle who had just killed one of my Barred Rock hens. The chickens are kept in small pens called chicken tractors that are moved around the garden where they can eat bugs and scratch up weeds. The wire at the end of this pen was loose. It looked like the chickens had tried to escape the eagle by forcing their way out of the pen. Last spring I chased an eagle away twice who was chasing my chickens, probably the same one. Once it actually grabbed one and tried to take off with it. But a full grown Buff Orpington, like the ones in the picture, is too heavy for an eagle to get off the ground with, so as soon as it saw me it dropped the chicken, who ran for cover and survived the experience. I rarely let the chickens loose to run around just for that reason. In the evening when we are around I will often let them out for a couple of hours. Once chickens are used to sleeping in their pen they'll go back there when it gets dark and I can shut them up again.