OK, my hanging plant has become Party Central.
Came home, peeked out my blinds and saw momma bird, two big fledging heads, then, as I was watching 
another dove flew in for a landing and the momma bird waddled to the edge of the plant, then flew off!!  It's like they traded places.  

I don't recall reading that male doves hung around to help out.
Could it be - the gods forbid - as 
Jess suggested?  Generation two already staking out the nest for the next brood?