Does anybody know what to do, or indeed if you can, help a chick that's fallen out of it's nest?

There's one on the high walkway on Cowley Bridge Road. I tried to help him up, but there's he's too young to do himself any good, and he wants feeding too, but I didn't have any dead insects on me. So he's just scrabbling at the air, which is no good, and a cat will have him soon.