start with keeping the dog confined or on leash at ALL times. Do not give the dog a chance to learn that chasing the birds is fun.
With the dog on leash, start at a great enough distance that the dog just notices the birds. Say "leave it" and reward the dog when he looks at you instead of paying attention to the birds. Keep working at this distance until the dog is reliably ignoring the birds and following your commands
Move a few feet closer and start again. If the dog ignores you and focuses on the birds, back up a few steps and start again.
Repeat this pattern, always with the dog on leash, until you are right next to the birds. If you plan to free range, let the birds out and, with the dog at a distance, work again until the dog is reliable.
Let the dog off leash, but under close supervision. This is where you will really learn if you are going to have to have the dog always leashed/confined when the birds are around. Some dogs have a much higher prey drive and can't be trusted off-leash. The temptation to jump on the little squeeky toys is just too great... Never ever leave your dog unsupervised off-leash or uncontained around the birds.
If the dog DOES kill a bird, pick up the remains. Gripping it firmly, smack yourself violently around the head and neck while screaming "bad owner! Never leave the dog unsupervised"