I have been doing this for 8 years now and I was wondering if anyone else in cold climate regions experiences significant "early spring mass suicides"....where bees fly out on a decent day and 50-100 land on the ground and on the hive stand and then just walk around slowly and group together in small clusters. Then as they day gets colder they start to move really slowly and chill overnight and die. They look like mostly larger older bees and my speculation is that they either don't have the energy to get back up to the hive because the temps are still in the low 50's range, or they are instinctively culling themselves from the hive because they are too old. I hate to lose these quantities of bees every time we get a nice day in early spring, but they seem to do it every year and the hives survive just fine. I've even tried "saving some" by putting them back at the entrance to see what they do, but they seem determined to kill themselves and either stay out on landing board or walk off the edge.
Anyone else observe this phenomena and/or have any why they do it?