From wildlife link above, it seems to depend on the age of the bird.
FIRST MAKE SURE THE BABY BIRD(S) IN QUESTION ARE TRULY ORPHANS: It is a myth that if you touch a baby bird its parents will reject it. Birds have a very limited sense of smell and will continue to feed a baby bird that is placed back it its nest by a human. If you cannot reach the nest, you can place the baby bird in a woven basket and hang it securely on a nearby branch. Be sure to prop the bird up a bit with leaves or grass so that the parents can reach it. Parents will continue to feed their baby if given the chance. Many baby birds learn to fly from the ground up. A fully feathered baby bird is considered a fledgling and many parent birds continue to care for their babies after they jump out of the nest. It is important to keep pets indoors during this period.
WHEN YOU FIRST RECEIVE AN ORPHANED BABY BIRD, MAKE SURE IT IS WARM: Tiny newborns without feathers do best with a heat lamp with a 40 watt bulb at least 12 inches away from birds and should be placed above an aquarium. The newborns should be placed in a small basket, margarine container, or bowl with toilet paper to prop them up a bit so that they can defecate over the edge of their makeshift nest. Place the "nest" inside an aquarium to simulate an incubator.
ALTRICIAL BABY BIRDS (THOSE WHO DEPEND ON THEIR PARENTS TO BRING THEM FOOD) NEED TO BE FED EVERY HALF-HOUR: Birds feed their babies constantly throughout the day. Anyone who has raised a baby bird can appreciate the diligence of parent birds. Never feed milk to a baby bird! For most baby birds a mixture of mynah bird pellets or dry dog food soaked in hot water, with a bit of baby food, turkey, and cooked egg yolk and a bit of water (until it is the consistency of oatmeal) will provide them with adequate nourishment. When fed this mixture baby birds will not need additional water, except maybe a few drops to rehydrate them when they first arrive. A popsicle stick or straw will work well as a feeding implement. Be sure not to over-feed baby birds, feed only until their crop on the side of heir neck appears full. Most birds, including fruit-eating birds, feed their babies insects to fuel their rapid growth. Baby birds will sleep through the night and do not need to be fed, but they should be fed before you go to bed and as soon as you wake each morning.
CARING FOR FLEDGLING BIRDS: As their eyes open and their feathers begin to emerge food should also be placed in cage to try to get them to eat on their own as soon as possible. Natural foods should be introduced as soon as birds are fledglings. Once eyes are open and the baby is fully feathered it is considered a fledgling. It will now need to be placed in a larger area with a perch. Two laundry baskets placed over one another work well.
Branches can be placed through holes for perches. Newspaper can line bottom. Don't use towels with birds since their claws can get caught in the loops. Once birds are eating on their own they should be placed outside in a cage that allows them to fly and is protected from predators.
CARING FOR PRECOCIAL (BIRDS WHO FOLLOW THEIR PARENTS AND FEED ON THEIR OWN) BIRDS: Baby ducks geese, swans, turkeys, grouse and pheasants fall into this category. A heat lamp should also be used for these birds when they are very young. A large cardboard box with high sides works well. Chick starter or turkey starter works well for these birds. It can be found at Agway and other feed stores. An upside down Mason jar on a plate with a slightly curved edge will provide adequate water for newborns. Water birds should not be allowed to swim until their downy feathers are replaced with adult feathers. These birds imprint very quickly. It is important that they not identify you as their mother and that they be raised with others of their own species!