DOn't give up so soon on your puppy! If ya didn't read it, I posted about a rescue GS, < 1 yr old. He was very lovely towards us, but had had some attack dog training. My oldest cat rubbed against him and then he tried to kill the cat. He tried to maul anther of my cats, now no longer with us. Then, he attacked my horse iN HIS STALL!!!! I took him back to the shelter before he started a massacre. It was PAINFULLY obvious that this behavior wouldn't fit in with our property. It is important to me that ALL of my animals respect each other.
I do not trust one of my dogs with the chickens, ALONE. My dogs live inside and help with the chores, so we have a great deal of daily interaction. This dog wouldn't dare kill a chicken in front of me, or bring it dead to show me. In fact, at 2 1/2 years old a dog should know what behavior is acceptable.
If you haven't buried the chickens yet, tie one around your puppy's neck for a day. These are BIG puppies so don't be afraid to bring her around your birds and smack her on the rump (ALWAYS avoid the face) the tell her definitively "NO!" when she is aggressive. Please spend TIME with your pup. He wants to please you. My dogs won't let ME out of their sight. It wasn't that way when they were puppies.
Stop free ranging your birds, because something is gonna get them, if your dog doesn't.
Sooner or later Americans are going to get tired of paying shelters to keep dogs and cats for months and months, so the next person who might own him might dump him at a shelter, and he might be euthanized. This sounds like a good natured puppy, but still, it's not going to be easy to rehome him. Horse people are very cognizant of re-homing (buying and selling horses) because hardly anyone gets their horses as foals and keep them until they die--it can be over 30 years, you know. We are in a line of previous and future horse owners of the same animal.
Dogs are much more sensitive than horses, and can become mean or very shy with subsequent re-homing, IF they are lucky.
DON'T GIVE UP ON THIS ONE!!!!