How to Return Babies to the Nest
Young "altricial" birds, (those that are born with their eyes closed, look pink, and are featherless), sometimes are knocked or blown out of a nest, or are pushed out by a sibling. They may have downy feathers (like peach fuzz), or some feathers on their bodies. These babies can be picked up and cupped in the hands until they feel warm. Once they are warm, they should be placed back up into their nest. It is not true that the parents will abandon their babies if they smell human scent. Most birds do not have a strong sense of smell.
Nests that are Destroyed
Sometimes nests are blown down by windstorms, knocked out of gutters, dumped from hanging plants, or destroyed by predators. Sometimes you cannot replace the babies because it is too high to reach their nest or the tree that their nest was in has been cut down. You can manufacture a make-shift nest with a berry basket or plastic butter tub (if you use a butter tub, punch holes in the bottom for drainage). If you can save the nest, place it in the plastic container. If the nest is gone, line the berry basket with clean, dry paper towels in a bowl shape. Do not use grass because it contains moisture that will chill the babies. Wire the "new" nest up as close to the original location as possible. You may have to put it on another branch or a nearby tree or bush. Make sure it is out of direct sunlight, or weather. Then warm the babies in your hands and put them into the make-shift nest. Leave the area and watch from a distance (or use binoculars) or the parents will not return. They may be skeptical about the new nest at first, but once the young start crying out in hunger, the parents will land to feed them.