Hmm, I wouldn't count on it. Both Boxers and German Shepherds have high prey drive don't they? He might get more used to seeing birds, but you may have trouble getting his attention while he's watching them.I imagine he'll outgrow it. I mean, its been winter for nearly 6 months and very few birds have been around. The last bird he saw was probably when he was 5 months old....they're probably pretty novel right now! Let him watch the birds. I think eventually he'll realize they're irrelevant and not that fun so high up, anyway.
Prey drive can be difficult to deal with since it's instinctive. I suggest building up his focus while the birds are a great distance away, then slowly get closer and closer as he succeeds. This could take a long time so go slowly. If it is prey drive (rather than just curiosity), it's not really something that can be trained out, but it can be managed.