Thanks for the message from Birdlady Susie. I did a google search today and found out that sometimes several females share the task of building the nest and use it communally. It said the nest can stretch to accommodate the eggs.
Today both Mom's have been sitting on the nest. My theory is that the second female that has been hanging around laid this third egg when Mom # 1 was off the nest. Now she sits on it and Mom #1 feeds the babies as the other bird is sitting there. They had a big fight this morning then seemed to settle down and both sat on the nest. It is cold and rainy here. I am attaching a photo taken from inside our bedroom showing both females on the nest. The picture is not real sharp. They will not let me photograph them when I am outside but it does clearly show both females on the nest.
Linda
