Yes it is perplexing!! Hopefully we will be able to see where they are going and if there is another nest somewhere. We were actually able to watch when the babies were first hatched and their next day journey down to the lagoon and our neighbors had a view of the empty nest, except for 2 eggs that never hatched, so a late hatching was not the case. We are even more committed to this investigation since even your sources are stumped!! LOL Will keep you posted!!