Blackbird Fledgling

We disturbed a cat with two blackbird fledglings in his mouth - he dropped both and raced off - one was dead but we have brought the second one home and it appears to have broken a leg but other than that is OK. He/she is still all fluffy on his head but is shedding and is trying to use his wings - I'm not sure if that indicates approximate age. We spoke to a friend who is a vet who said it was likely if we took him in they would just put him down. What should we do?