Thanks for writing. If you really think the parents are not returning, you could try to hand raise the remaining baby, but it’s a lot of work and I should tell you that according to the letter of the law, you’re not supposed to disturb bird nests in any way. Not that it’s likely that anyone would prosecute you for trying to save a baby dove, but just so you know.
Unless you’re really sure the parents aren’t returning and you’re really prepared to hand feed a baby bird every couple hours for several weeks, you should probably just leave the nest alone and let nature take its course. The sad truth is that sometimes parent birds get killed when they are away. And baby birds often don’t survive.
If you wanted to hand raise it, my suggestion would be to go to a pet store and get powered baby bird food and a bird feeding syringe. Any shop that sells birds is likely to have those. You mix up the powder with water and feed it to the baby with a syringe. I have found that it works better if you use warm water at first, and you may have to pry the chick’s mouth open and gently squirt a little food in the first few times. Be careful not to drown the chick. After a few times, usually the baby bird gets the idea and will begin opening its mouth for you, which makes things much easier. And after a bit, they don’t seem to care as much about whether the food is warm or cold. Once they are enthusiastically eating, you’ll be surprised how much food they want!
You also need to keep the chick warm, especially if it doesn’t yet have feathers. Let me know how you make out. Tom