Birds have a high metabolic rate and a high energy requirement. Bread crumbs and milk are not sufficient. Most baby birds are unable to feed themselves; normally the parents feed them, so putting bird seeds or worms in the box does no good. You have to put the food into the baby. At first you may have to pry open the beak to do this, but soon the bird will realize that you are the source of food ( mama ) and will open its beak and squawk whenever it is hungry or when it hears you approach. Feed it when it asks for it. When it has enough it will collapse and sleep until it is hungry again.
A warning: be VERY CAREFUL not to get any food underneath his tongue. That is where his airway is and if food gets lodged in there he will choke. When he opens his beak, just make sure that you take your time to put the food above his tongue, preferably near the roof of his mouth. Just relax and don't worry about making a mess, because baby birds are very messy.
The majority of birds can be classified in two groups: meat eaters and seed eaters. Basic diets for these are listed below with suggestions for special foods for different species of birds. The sooner you identify the bird, the sooner you can provide the best diet. The basic foods mentioned in these diets can be classified into two groups:
MEAT: high protein dry kitten food (soaked in water), boiled chicken, live insects such as flies and mealworms.
GRAIN: high protein dry baby cereal , wheat germ, corn or oat meal that has been powdered down in a blender.