I went to remove the nest and eggs this morning. All 4 eggs were gone. No sign of any attack and I have a spooker and baffle up. I suspect Momma took the eggs out knowing they were no good. About an hour later I found one egg about 50 feet away near my milkweed garden. It was slightly cracked and I opened it up. There was a very deformed almost mummified embryo that looked to be no more than 5 or 6 days along which incidentally coincides exactly with the cold snap we had. I suspect the Gilbertson box is not as insulated as the slot box (all 5 eggs survived and fledged MUCH colder weather last year).
The GOOD NEWS is Momma and Pappa have been very active around my slot box this morning so I am very hopeful she will start building again soon.
Such is the life of an EABL Landlord!! The highs and lows. I must say that this is the first failure in 7 years. My Blues have fledged over 40 babies in the past 7 years so one failure like this is not a bad percentage in hindsight.