Oooh look at that face!! That's the face of a GOOD dog. Of course we don't know what's going on in his mind.
I would always keep him leashed around the chicks - it's easier to prevent an accident than try to train the bad behavior out of him. Never give him a chance to be unsupervised amongst the chickens.
Keep him leashed with you while you go about your coop chores. He looks like a young pup so he is very capable of been sweet and serene one minute and racing thru the flock to grab a flighty bird the next. That's the nature of dogs even if they don't have any hunting stock behind them.
I don't mean he has to be on lead for life but, mainly till he matures and works out some puppy exuberance. You must constantly watch for signs that he is too interested in the birds, like panting while he watches their every move, or quivering because he is dying to chase them but, he knows you are there.
I'm sure more experienced people will be along to add their suggestions. Have to mention again, that is one beautiful pup.