I just got my 57th call for this week that was prefaced with “I found a baby bird”. My other favorite variation, “I rescued a baby bird”. You may not like my response but PUT IT BACK. Baby birds are fledging, that means they are learning to fly and they do that by jumping out of the nest. Not how I would do it but Mother Nature has set it up this way. We can’t teach a baby bird how to find food, what to fear or find a mate. Only the parents can. By taking in baby birds that are not injured, feeding them, protecting them, they become imprinted. Once they are released, all you have accomplished is delaying their death from attack or starvation.
The parents are close by and want their baby, as attested to by the lady that was attacked by a mockingbird, while “rescuing” a fledgling mockingbird baby. The parents can’t pick it up but they can feed it and protect it. So pick it up and put it in a bush or back in the nest if possible. Count on it, it will jump out again.
If it is bleeding or otherwise obviously injured, call a rehabber in your area. By the way it’s a myth about parents smelling you on their baby and rejecting it.