Injured birds are meant to be handled only by qualified, licensed rehabilitators . It is against a lot of state and some federal laws to take in a a sick bird and try to heal it yourself. This includes native species and particularly raptors because of the danger they may pose to people.
If you see a lonely bird or a fledgling on the ground, odds are it's NOT abandoned, just in training and the parents are nearby.
If you find a nestling that has fallen from it's nest before it can fly the best thing to do it to place it back in the nest because birds have a bad sense of smell and probably won't know it was handled.
A whole nest should be placed back in as close a spot as you can tell it originally came from.
