Well, it is in their blood... Whether bird dog, hound or shepherd, prey drive is bred into most of our pets, it was their reason for being. Some can be got over it, but only if they are started early or unusually untantalized by chickens. I'd say it would be the unusual dog who would ~not~ be a chicken killer if given the free opportunity.
My friends Bob and Kay had an early bit of marital tension when she moved in with ducks and geese and he had bird dogs. He wasn't about to punish his dogs for killing birds. And seeing how much prey drive Gidget has, I wouldn't try to get birds here. It's just a losing battle.
Don't you think there is a difference though? All dogs have hunting instincts. Cindy will chase any rabbit or rat that comes in her yard. She won't bite heads off of them or attack me if I check her though. She would run at the first time someone yelled at her. It's hard for me to explain but it's like they just want to kill vs hunting. Very aggressive animals.