Exploring the mystery
Today was the warmest day since last November! It was nearly 70 degrees this afternoon. I had gone out to the gravel pit in the morning and started opening the hives to see what had happened to them. If my theory about the concrete activity in the pit is correct, I would expect to find lots of honey on the hives, but few to no bees. That is pretty much what I found. The horizontal hive had at least seven full frames of honey and it did have a dead cluster. The insulated hive was completely empty. No bees, no honey. It did have debris from robbing and some dead bees and yellow jackets on the bottom board, which suggests it was robbed out in the fall. The next hive over that had a resident mouse must have died before the mouse moved in. The mouse was only in the bottom box and really had not done too much damage. It had made a nest in foundationless frames, so there was very little clean-up. Two mice ran out. The nest was easily shaken from the frames and box. There were at least three boxes with honey, two completely full. This suggests this hive died very early. There were really no bees, no cluster in this hive. The little split had pretty much all its winter honey still on the hive. There were very few dead bees on the bottom board.
By afternoon when we went to pick up the equipment, there were robber bees out in the equipment. They weren't bothering the capped honey, but were after liquid honey and perhaps pollen??? We picked up most of the equipment, but left some boxes on their sides because of the robber bees. We will pick them up when the bees aren't out, like during the morning some day.
I have been told that bees do their best to exit the hive to die so they don't make more work for the other bees to take them out of the hive. So, my theory is that they left the hive to die until they dwindled to the point where only a small amount were left and those died and fell to the bottom of the hive. Only the horizontal hive had a cluster. All the hives except the foam insulated hive had honey left on them. That one must have been robbed out because it was pretty much empty.
So, I have chosen a spot on my property to move the experimental hives. We will set them up in a month or so and do our field days there. I will give directions on my email list.