Songbirds
  Altricial birds (songbirds, owls, et al.) are hatched naked, blind and helpless.  The parent birds work all day to bring their young food.  The young will "gape" for food when the nest or branch the nest rests on is disturbed, and this signals the parent to feed it.  At 3-4 days of age, the young begin the period of their most rapid growth.  Branch-nesting birds are capable of leaving the nest in a fluttering-flight at about 11-12 days of age.  Cavity-nesting birds will leave the nest at about 16 days of age.  However, it may be 10 days to 2-3 weeks before the birds is fully flighted, self-feeding and independent of its parents.
  It is during this "fledgling" period of fluttering flight' (10 days - 3 weeks of age) that most unnecessary rescues of young birds occur.  Fledglings typically have feathers that have emerged from the quills but their tail feathers may be shorter than older birds.  During fledgling they will emerge and test their "mettle"  with short flights in which they often wind up on the ground.  They will call to their parents who will still come and feed them and encourage them to flutter to nearby branches.  This is a period of skill development & learning for the young birds.  When people, especially children, find fledglings on the ground, they assume that the bird if abandoned.  This may not be true.  The best plan is as follows: if you find a downed fledgling, leave it be, making certain that  no present danger exists for it, ie: bring the cat or dog indoors for the duration.  Watch the bird for about 30 minutes to see if a parent bird comes to it.  If no parent arrives, you  may: 1) locate the nest and gently place the youngster in it; 2) create a temporary nest using a plastic berry box lined with some soft, clean paper towelling, gently place the baby in it & hang or securely place the nest in the tree you suspect the bird fell from; 3) gently place the bird so that it can perch on a branch of the tree, preferably out of reach of cats.  If, after observing the bird for a while longer (1 or more hours) you have not observed parental return, assume the bird to be orphaned.  NOTE: Your observance of the bird should be from a window or from a good distance away.  The parents may not return if you are hovering nearby.
  If the bird is an orphan, or if flies are buzzing around it or it is in danger or clearly injured, you may provide the makeshift nest box for the fledgling, place this inside a cardboard box with air holes punched in it, and place a screen top over the box.  Keep this in a dark, quiet, temperate area until it is possible to transport it to the nearest licensed wildlife rehabilitator or veterinarian.  DO NOT attempt to feed or give water to the young bird.  Let it remain undisturbed but do get it to the proper person for care ASAP.  It doesn't take long for a young bird to dehydrate or get hungry, but a trained individual should be the one to determine the proper course of action..
 Wild birds are delightful to watch, but they do not make good companion  animals, and it is a violation of federal Law to hold a bird for any length of time without the proper permits.  Please call your local rehabilitator.