The St. John the Divine nest has a deep slope that allows the eyasses to completely hide from view. Since we discovered the second eyas on Sunday, there have been clues that a third eyas might be in the nest.
Today, the puzzle was solved. We finally got to see all three at the same time. Once during a morning feeding and again in the early afternoon.
Update: Since June 1st, we've only been able to see two eyasses.