Robin Update

So, here's what has happened (and not happened) since I last posted:

• We have had no other babies fall out of their nest.
• All three babies seem healthy.
• The baby that fell out yesterday is completely fine (we think).

But the sad thing is this -- when the babies hatched, there were four. But now, there's only three. Why? Because (this is all we think, OK?) the fourth one hatched the day after the others, and so didn't get enough food. And for a baby bird, every day counts. So basically, its the runt. 

Yesterday we only saw three heads come up at food. We wondered if the fourth was dead, but we didn't know for sure. But last night, we saw the mommy robin pulling it out of the nest. 

So what do I think happened?? This:

I think that, as the one baby fell out yesterday morning, it was pushing away when it that its little baby sister/brother was dead, and it went too far and fell.

What do you think happened?