The bad news is that you really have to
always keep him on the long line
...and I mean for maybe months or even longer. Every time you let him off and he gets self-rewarded by chasing again, all prior training goes down the drain. Get a really long one, 50 feet or so. You can let it trail so he has just as much freedom to run around to his heart's content except that when you see birds/rabbits/sheep or whatever it is, pick it up and practice the recall. He will also learn to stay within an acceptable distance from you.
I know it's frustrating but I think it's a very humane and effective way of preventing these chasing situations which can be dangerous for all involved, and distressing for you.
Jerry was super difficult at that age (around his first birthday) and tbh, I still keep the long line on in some areas with a lot of wildlife. He is three now. I'll never forget one situation in which he was off to chase a hare and a truck was barreling down at the other side of the field on a rarely traveled country road. The hare barely managed to cross the street safely. I know Jerry would have been run over -- if it hadn't been for the long line. That's what I remind myself of every time I get tangled up in that dirty long line, it gets wrapped around a tree or whatever else. It's great for training and even better for preventing. Just keep it up and it will pay off in the end