Some very sad news to report: the sparrow, whom I'd named Jack, died last night. I don't know what happened, whether it was stress, lack of eating, an internal injury, a combination of those things, or something different altogether. I spoke to the vet who'd come by on Monday and he said that small birds like Jack tend to die easily when they're suffering from trauma.
Suffice it to say that it breaks my heart, but I'm also so appreciative of everything you all suggested. It's good to know there are many animal lovers on this list.
Thanks again.