I've raised quite a few baby birds, some newly hatched.  I raised a couple of 
newborn starlings that thrived on a mixture of dog food, egg yolk and de 
fatted wheat germ.
The dog food was a regular canned beef based food.  The egg yolk was hard 
boiled and added to the dog food.  I'm not sure of exact proportions, but say a 
tablespoon of dog food, a tablespoon of egg yolk, and some wheat germ sprinkled 
in.  Then I added some spring water so it was not too dry.  It had a wet 
consistency, but it was together enough to form a little ball and put on the 
end 
of a drink mixer. I used the drink mixer as a feeding device to get the little 
ball of food into the babies mouths.
They only take a couple or so balls of food at a time.  You must not overfeed 
them.
But, and here's the hard part, when they are naked nestlings, they have to be 
feed at least every half hour from sunrise to sunset.  Some feed every hour, 
and that is the absolute maximum time that can elapse between feedings at that 
early age.  I was doing it every 20 min.  They let you know if they are 
hungry or not.  Mine were healthy, so they would open their mouths and scream 
to be 
fed.  When they were full after 2 or so little pea size balls of food, they 
would just shut their mouths and not cry for any more.  As they get older and 
get feathers, the feedings can be farther apart.  They MUST be kept warm.  That 
is extremely important.  They should be put in a room that is around 85 
degrees.  A good nest is a coffee filter filled up with Evercare paper cat 
little.  
It's very soft and nontoxic.  It must be changed all the time to be kept 
clean.  
Do not try to give them drinks.  Give  moisture by dipping the little balls 
of food in water before putting it into the mouth.
You have no idea what kind of bird it is?  The same food would be appropriate 
for sparrows, starlings, etc....
Summer