Every summer, we receive numerous phone calls at NBNC from people who have found baby birds out of their nests, wondering what they can do to help. Not only is info on baby birds often lacking, but there is a lot of misinformation with regards to the proper course of action.
It is a natural part of most songbirds' development for them to spend some time out of the nest before they are capable of full flight. During this time, they are often still cared for by their parents (who are often watching from a bush or tree where you can't see them). If the bird is fully feathered, it is likely at this stage in its life and no intervention should be necessary, aside from keeping dogs and cats away.
If the bird is not feathered, returning it to its nest may be the best option, so look up and see if you can find/reach the nest. Contrary to popular belief, baby birds will not be rejected by their parents if handled by humans. It can be very difficult to tell if a baby bird was abandoned as parents will often stay away if they see you nearby, and go through every effort not to draw attention to their young. If you know for sure that the bird is abandoned (ie, mom was eaten by the neighbor's cat) you should find a trained wildlife rehabilitater, as baby birds require specialized care. You can contact the Nature Center for this info.
This short post gives a brief introduction to a few of the different scenarios that can unfold when a baby bird is found, but should you need further advice, please see the additional resources provided below: Mass Audubon