A baby bird may be blown out of a nest by weather, or even dropped after a failed predator attack. If you find an uninjured baby bird that is not fully feathered, search the area for a nest and if possible* place the chick back into the nest. Watch the nest from out of sight for 1 to 2 hours to confirm the parents are returning to feed their young. If the parents do not return and you see the baby is in distress, call your local rehabilitation centre and discuss with them whether to give the parents more time to return, or to arrange to have the young brought to their facility.
*If you can't reach the nest you can use a makeshift nest from a berry basket with grass or small towel lining a shoebox or margarine container. This can be placed >5 feet off the ground securely on a branch or in a bush near where the baby was found. Observe this nest from a distance for 2 hours and look for signs of activity from the parents. If the baby is calling out, the parents should be able to find it and may continue to feed it. If the parents never return, the baby may be abandoned and you should contact a local wildlife centre.