1) If the baby bird is not on the ground, leave it alone. It is probably learning to fly and the parents will continue to feed it.
2) If it is on the ground, unless it is in immediate danger from predators, eg:- Cats, or traffic, it is better to keep a close eye on it for a couple of hours to see if the parent attends to it, bearing in mind that the parent bird will take just seconds to feed it before flying off in the search for more food.
3) If the baby is in danger place it in a warm, dry box which has plenty of ventilation. Poke holes in the box before putting the bird in. If the box is lined with newspaper and a towel placed over the paper, it will make it easier for the bird to grip. The box could be placed on a hot water bottle to help keep the baby warm.
4) It is important to handle the bird as little as possible. It is difficult to see if a bird is stressed and it may seem quiet and calm but it will be extremely stressed and when in that stressed state it’s body will be releasing the hormones Catecholamines and Cortisol which will slowly damage the birds health.
5) Do not try to give the bird food or water at this stage and do not put any container of water in the box. The bird can easily fall in it and either drown or become quickly chilled and die of hypothermia.
6) When transporting the bird it needs to be kept as quiet as possible to keep stress levels to a minimum. It does not need you talking to it or playing music.
7) It helps a great deal if you call in advance before bringing a bird so that necessary accommodation can be prepared.