At some point, nearly everyone who spends time outdoors finds a baby bird—one that is unable to fly well and seems lost or abandoned. Our first impulse is to adopt the helpless creature, but this often does more harm than good—and in most cases, the young bird doesn’t need our help at all.
The first thing to do is to figure out if it’s a nestling or a fledgling. If it’s sparsely feathered and not capable of hopping, walking, flitting, or gripping tightly to your finger, it’s a nestling. If so, the nest is almost certainly nearby. If you can find the nest (it may be well hidden), put the bird back as quickly as possible. Don’t worry—parent birds do not recognize their young by smell!
If the bird is feathered and capable of hopping or flitting, and its toes can tightly grip your finger or a twig, it’s a fledgling. Fledglings are generally adorable and fluffy, with a tiny stub of a tail. It’s easy to jump to the conclusion that the bird has been abandoned and needs you. But fledglings need a special diet, and they need to learn about behavior and vocalizations from their parents–things we can’t provide.
Fortunately, the vast majority of “abandoned” baby birds are perfectly healthy fledglings. Their parents are nearby and watching out for them. The parents may be attending to four or five young scattered in different directions, but they will most likely return to care for the one you have found shortly after you leave.
When fledglings leave their nest they rarely return, so even if you see the nest it’s not a good idea to put the bird back in–it will hop right back out. Usually there is no reason to intervene at all beyond putting the bird on a nearby perch out of harm’s way. Fledglings produce sounds that their parents recognize, and one of them will return and care for it after you leave.
If you have found both parents dead or are otherwise absolutely certain that the bird was orphaned, then your best course of action is to bring it to a wildlife rehabilitator. The National Zoo has excellent information on emergency care until you can get an injured or truly abandoned bird to a wildlife rehabilitator.