If you find a baby bird with little or no feathers, then it will need help.
Replace into the nest: If you can see the nest, the bird has recently fallen and does not appear injured and is warm to the touch, you can attempt to replace it into the nest. Keep an eye on it though to make sure it does not fall or get pushed out again later.
Contact a wildlife rescue centre: If you cannot find the nest, or the bird is injured/appears ill or cold, transfer it to a secure box and bring it indoors somewhere warm and quiet. Do not attempt to put food or water into the beak as it can easily get into their lungs if this is done incorrectly. Contact a wildlife rescue centre or vet who will be able to give more specific advice and arrange for someone to hand-rear the bird.
Many birds that appear in need of rescue are actually fine. Please take the time to assess the situation before stepping in to help. Fledglings (with feathers and mobile) often leave the nest a few days before they can fly, and you may see the young birds sitting on the ground or hopping about without any sign of their parents. The parents stay close by but leave their babies to practise fending for themselves. It is very traumatic for these birds to be taken and hand-reared by humans unnecessarily as they have already become used to the parent bird. The only time fledglings should be interfered with is if they are in immediate danger (eg. in a road), they are injured, or if they have definitely been abandoned or orphaned (parents are extremely unlikely to abandon their young and are probably just out of sight or collecting food elsewhere).
Tawny owl chicks are mobile at a very early age and can be seen climbing in and around their nest tree well before they are able to fly. If you find a fledgling or young owl, the best thing to do is to leave it where it is unless it is in immediate danger or injured.
Any bird that has suffered a cat attack will need to be treated with antibiotics as well as treatment for specific injuries sustained – even a small scratch can lead to infection. Place it into a secure box (in a warm and quiet location) and contact a wildlife rescue centre or local vet for advice.
If a bird appears to be sick or injured, it will need help to recover. Again, place into a secure box (in a warm and quiet location) and contact a wildlife rescue centre or local vet for advice.
If the bird has flown into a window and is unconscious or dazed, they may recover whilst inside the box. Check on the bird after 10, 20 and 30 minutes and, if it appears to be fit and alert at any point, attempt to release into the same location (this will avoid the stress of being transferred into care). If this fails, there may be an underlying injury that requires treatment. Contain the bird and follow the advice above.