OK, we have an Observation Hive, a four framer, four frames high. We have a marked queen in it. We had noticed that even though the queen has been laying since Feb. the population seemed smaller than in the Winter when we put them in it. I thought maybe they just seemed like less bees because all the brood was on one frame and the bees were all on that frame. While there is mostly drawn comb in the other three frames, queen never laid eggs anywhere but the one frame. A few days ago I noticed different waggle dances. Longer periods of vibrating in place before doing the half circle stuff, and they didn't have pollen. That coincided with them ignoring the 1:1 syrup in their feeder, so I thought they must have found a good nectar source. Then yesterday my wife noticed that the queen wasn't laying eggs as much as she used to. She was just kind of hanging around. Then this morning they were all very excited, lots more bees doing the extreme waggling....I thought they must have found a great nectar source. While it is hard to see in the cells when they are covered with bees, my wife still noticed that all the cells that glistened with stored syrup/nectar before seemed empty... A few minutes later, about 10:00 this morning, they all rushed the exit. Craziness. I thought it was odd, they hadn't gotten honey bound and didn't seem to have a big enough population to swarm, and with the Observation Hive mostly empty, it was easy to see that there were no swarm cells. Some capped brood was left, no open brood. There were still a hundred or so bees left, and they are currently opening capped brood and carrying larvae around. The marked queen and most of the bees gathered on the wall at the hive's entrance outside. I sprayed them with syrup and brushed them into a box right under the hive entrance. Those are my immediate observations while they are still fresh. I can upload video to Youtube later when I get a chance.... I wonder if this was typical Spring Dwindling and an absconding that was unrelated to the fact that they were living in an O.H., or what...The reason we put these particular bees in the O.H. to begin with was because they were a punky late swarm from the Fall. Maybe they just never were able to get their numbers up or something? I know if we hadn't been looking at them, we would have just had an empty hive today and no clue why. Actually, we were looking at them at the time and still have no clue why. What do you think?