We had a hound/heeler--she'd round them up, then chase them. We introduced her to each chick (and bunny), telling her "nniiice". She accepted each as a member of our 'pack.'
Now might be a good time to dog/bird bond, having them both share your time together. (And, yes, he will sniff her butt--kinda creepy, but hilarious) He needs to learn mom's fluffballs are not toys and must be treated gently. Also, do NOT give him toys that are furry or squeeky--his tiny doggy brain won't be able to differentiate.