how old is he? what kind of prey drive does he have? does he know "leave it" ? Do you mean trust him outside alone or under supervision?
Really, it depends on all of the above factors. Rayden is the most trustworthy dog ever, but I never leave him with any other animals unattended.
The simplest solution (but still takes some time to train) is to teach "leave it"
put the dog on leash and go just to the point where the dog shows interest in the birds. When he shows interest say "leave it" and give a leash pop. when he looks at you say "YES!" and give a treat. After he is good at that distance at ignoring the birds, move a bit closer. If you find that he can't/won't focus on you, move farther away and practice there.
If he is tied in the yard, what exercise/play time does he get? Chickens aren't smart enough to figure out to stay away, so you will lose them if they wander over there.