I have the same thing here.  I suspect they have gotten a meal or two out of my flock since I had lost some a couple of weeks ago, and it had to be during the day.  
Just two days ago I was working out in the yard and heard one of the roos warning the flock and sure enough, it wasn't long after I saw a Bald Eagle up above.  Funny though, the 5 or 6 crows that were hanging around the field went right after it and chased it off.  I had read somewhere that crows are great for keeping flying predators away from your place.  Unfortunately, that comes with a cost too.  
I love seeing Bald Eagles, but I sure wish they would find their food elsewhere.
I think the only sure way to keep from losing them is to have a covered run.  If you free range, then you are taking your chances.