I have an elderly friend who has a kelpieXborder collie that she uses to herd her rhode island red chickens every afternoon, and in the morning there is one pair my friend likes to keep locked up, and she can make the dog keep them separate so that they stay in the pen, or herd them back in if they got out. It was quite amazing to watch it, however the dog could get incredibly rough at times where she gets overly excited or a chicken tries to fly over her and she will grab their tails and pull them down, which my friend has to command her to quit it.
Has no history of killing anything, but her herding instinct must have seen grabbing them as the easiest way to keep them in line, but it's not something she wants the BC to do. There was also concern with little chicks following their mother and the dog sometimes frightened the chicks and they'd scatter from the mother hen, so obviously the dog would move quickly to where the separated chicks are, but she never got a chance to grab them with her mouth (as the lady calls her to stop whenever that happens, we don't know what she does otherwise).
So I guess it's something you have to really trust your BC on and spend a lot of time together with the dog and the birds until you feel confident that nothing will die. I have a border collie who I have as a running buddy but shows great interest in herding (for some reason any maltese/shitzu like dogs always get herded and overwelmed), however I do not feel confident in training him with live chickens (as I have no access to cattle or sheep) so I will not. He did well with ducks when I had ducks but chickens can fly over his head and from seeing my friend's BC jump up and snatch them out of the air, I don't want my birds to deal with that stress. However in the next week I am taking another BC puppy home which I am going to raise out in the backyard where the chickens are so I can try it with a young dog. Let the pup grow up with the chickens like how you'd train a Mareema Sheepdog, so it sees them as family. Luckily for me, my chickens are not at all affraid of dogs as my jack russell often is let out the back to kill rats, and the chickens hang around for any cockroaches that come out from boxes I move for the jack russell to find rats; and she isn't interested in killing chickens which helps.
Also make sure your BC gets walked amply. If he gets bored, there is a chance he might just start destroying stuff or even killing.
The main issue I'd see is like my friend, the high energy of a BC would most likely be more intense for chickens, and their size seeming threatening towards the chickens. Maybe a smaller herding breed like a corgi might be better? However I think they nip quite a bit so I'm unsure.
By the way, no idea how old this thread is, so sorry if it's like several years old.