There’ not very much you can do in a situation like this, just let nature take its course.
I have probably over a years supply of food for myself in storage.
Watching an animal starve and die when I might be able to do something is against every fiber of my being and would haunt me till my last day!
Bullsh!t
We had this happen to us a couple of years ago. My daughter (now 11) took charge. We placed the sparrow is a small box. My wife picked up baby bird food at a pet store and fed the bird. It grew and grew. The bird was tame and we eventually released it.
My daughter still looks to the sky and speaks of Feathers.