I had posted excitedly on Saturday that only one of United Nectar's urban apiaries had not survived the winter. After partially-disassembling most of the hives on Saturday, I can now report that the Davnie Hive is also dead.
Unlike the Hilty Hive, which had recently perished, the Davnie colony seems to have been long dead; the odor of decomposing bees alone told me that. Though both the Hive Host and I had witnessed loud buzzing and many bees coming and going as recently as the day before, I now believe that these bees were robbing any honey that might have been left in the defunct hive, of which I found a small amount.
The Davnie Hive was a late installation due to the tornadoes in Spring 2011 that delayed the arrival of the Buckfast Carniolan bees that I had ordered through Cannon Bee. I can only think that this colony didn't get well-enough established to make it through the winter.