Nope, not once.  And we have a truck load plenty of them.  The last place I lived had more raptor life than I had ever seen in my life...every specie of hawk one can imagine, bald eagles and even a pair of osprey living next door.  No losses.  Just that one bird to a Great Horned Owl and she was out of reach of the dog's defense, so she was risking her life by refusing to roost in the coop. 
 
Good cover, good dogs, good roosters, flighty breeds/chickens who have been on free range from the earliest age...it's all a good combination.  I wouldn't free range any other way. 
 
My sister used to breed mini doxies and her pack was downright death on anything that moved!  They killed her chickens, her ducks, her geese, even pulled a mini goat's head through the fence and killed it.  They not only killed her cats but ate them as well.  Nicest little dogs you can imagine when they were by themselves, but as a pack I'd hesitate to put a baby out in the yard on a blanket and turn my back on them.