If you've found a baby bird, the best thing to do is take it to a vet or a wildlife rehabilitator as soon as possible as they belong with their mothers and is extremely fragile in their early days. If you feed them the wrong food or feed them in the wrong way, you are more likely to cause the bird damage or kill it quicker than if you hadn't fed it at all, so it is best to get professional advice if possible. If they are bald and without feathers, they are nestlings and should be returned to their nests, which should be directly above where they were found, usually high in the trees, although it might be difficult for you to return them to the nest without a ladder or other help. It very much depends what type of bird it is as to how long they can survive without food and what the best thing to feed them is, and the British Wildlife Helpline website offers a good range of advice on how to look after and feed different birds. It mentions that if you have found a nestling (i.e. A partially feathered or bald bird), the first feed should not be given until the bird feels warm and appears alert and rehydrated. If they are very small they may need feeding in half-hourly intervals, although it is best to feed them too little than too much. For birds that gape (look up with their mouths open ready for food), you should use tweezers to give them tiny amounts of food and be sure that they have swallowed each piece before giving more as they may choke.
