1. Guarding livestock, as opposed to playing with them, is NOT NOT NOT instinctual. Yes, they like to guard things they consider "theirs," BUT it takes many many months (even years) of training to channel these instincts into appropriate behavior. It takes a big training commitment to get them to behave appropriately in a consistent manner, to the point where you can leave them alone with birds.
2. Do a search on here for Mountain Man Jim's posts on LGD training. He has a very good method.
3. The dog will first need to demonstrate a modicum of obedience, which means some obedience training is in order. The dog needs to know to obey you when you say "come," "leave it" or "guard". Pyrs are notoriously stubborn and independent--the same corrections that work perfectly on other breeds may not do a darned thing for a Great Pyrenees. E.g., I have used the same exact obedience methods on my Newf and my Pyr. The Newf obeys like a giant drooling angel, and promptly attends to me, heels, sits, shakes hands, kisses, rolls over, makes an effort to learn carting commands and shushes on command, and I rarely have to tell her twice. The Pyr might listen to me...if he knows I have a pocketful of treats. If there isn't a threatening traffic helicopter that might swoop down on us and steal a chicken at any minute. If a neighbor kid isn't knocking on the door to sell us popcorn. And I can snap that prong collar all I want, he is not especially impressed. You have to do obedience when they are young, so it sinks into their brains a bit. And be prepared for them to spontaneously forget when they are 9-18 months old, as teenagers often do.
4. Your dog is still very young. Puppies naturally want to play. At this stage, you can tether one end of a 6 foot leash to your belt loop and have him heel to you while you do your normal chicken chores, and make him behave while you do that, so he understands this is serious business. But for sure, don't trust him with them off-leash. It takes time and patience and training, and the dog isn't really going to be ready to guard properly until he is at least a year old--and maybe more like 2 years old. The good part is, once trained, they are wonderful guardians, and they tend to be very long-lived so it's not like you have to do two years of training every five years or something.
Mentally, Pyrs are very much like cats. I love my Pyr dearly because I am very much a cat person, and having a dog that rolls over for me is not so important as having a deputy that can guard my house/property independently without my assistance. But if you're more of a dog person and really value a dog that obeys instantly, without question, or that does tricks, then probably a Pyr is not a good choice.
