I would keep an eye on him but not do anything at this point but when it comes to the point that you can't watch anymore, i would try to catch him otherwise, he'll just get eaten. I did hear it was a myth that the momma bird would reject him if you touch him. Not sure if that is true or not but would be worth researching. Years ago, one of our dogs grabbed a young bird that was just learning how to fly and we saved the bird from the dog and put him in a box and fed him worms with a knitting needle. After a few days, maybe a week, he just flew away one day. But not long after, he came back and chirped at us as if to say hello. It warms my heart to think of it!
