Baby Robin

I owe a world of gratitude to the members here. 5 or 6 years ago I rescued a baby pigeon. Due to everyone's help (from this site) Owl is a healthy, happy and bossy member of the family.

Now I have another question. There is a robin's nest in the trailer hitch of fifth wheel here on our property. There is only one baby robin in it. I am not sure if the other eggs didn't hatch or what, but there is only one baby. I work all day, but do check in on him/her several times a day. I used to see the mother or father rather frequently, but have not seen them lately. The baby is good sized, with feathers, but still also has 'fuzz'. Here is what I am having a problem with: I have not seen the parents lately and the baby hasn't moved in at least a day. It's alive because when I put a flash-light on it the beam makes it blink it's eyes. Other than that there is no sign of life. No movememnt, nothing. I used to be able to stand quite a ways a way and make 'kissy' noises and I could hear movement and peeps in repsonse. Now, absolutely nothng. No movement, no peeps, nothing. Should I be at all concerned? Of course, you can tell that I already am concerned, but I should I be more concerned? Could it have been abandonded? How long can it survive without intervention?

Am awaiting all your responses. Thanks so much!