You need to use some tricks to assert yourself as Alpha. Alpha with a capital A.
When he recognizes you as the all powerful and you tell him no, let him know that the birds are yours only, then he will stop.
Do the usual training for dominance.
Tie him to you. Have both a short lead and a long lead. (long long)
The only food comes from you in the form of treats throughout the day.
Make him work for every one.
Sit. Stay. Heel. Come. Repeat ad nauseum.
When he listens to commands or obeys correction, he gets a treat.
He will begin looking to you before he even draws a breath.
This is good.
Be generous with the praise and affection.
Take him out on the long lead to where the birds are.
Direct his eyes to your face.
Give praise.
Then walk.
If he looks at the birds, give a sharp, quick snap of the lead and say, 'NO'.
Direct his eyes back to you.
Repeat.
If he goes a good amount of time without tracking them with his eyes, give affection and approval.
Then let the lead out a bit etc...
What worked for my Australian Shepherd when she was plucking the birds was for me to keen over them. To be sad and refuse to look at her, turn my back to her.
She figured out quick that she was causing me great distress.
No more troubles.