I lifted this from the RSPB website:
"I have an injured bird in my garden, what should I do?
For most injured birds, place them gently in a box and keep them quiet, dark and cool. It may be that the bird is in shock and will soon recover so you can let it go. If it is more seriously injured, this will reduce stress on the bird until you can get advice on how you can help it.
The RSPB does not have bird hospitals or a rescue service because we are a conservation charity. The RSPCA, your local vet or a local animal rescue centre, have the expertise to help and advise you about sick and injured birds and animals."
hope it helps.
They will be as protective as they were before- it is sterilization, not a frontal lobotomy. No worries.