Any vet will pts injured wildlife free of charge for you
In that situation i would leave them to finish the job themselves, i would rather them do it than me. If they have something freshly caught and fully alive then i do my best to get it, i kept a fledgling last year for a few days before it went to live in rehab ready for release, was out digging worms in the early hours
Simon found a blackbird chick yesterday and the parents were going balistic at him, divebombing and screaming
i didnt manage to save it