[i*love*cooper]

I have been keeping an eye on a Robin's nest for around a month now and there is a strange story that goes with it. On April 13th, I noticed 4 eggs, a few days later only one. The robin still came to sit on the nest. Days went past until she disappeared from the nest with the single egg still there. A robin returned (a new one or the same one??) and 3 more eggs appeared. The robin has been sitting there more definately 2 weeks, maybe more. Will these eggs hatch? Is there a chance the eggs are not fertilized?

I am curious if an animal is messing with her nest and is it possible that there could be two different Robins occupying this nest?