I'm overwintering a single 10-frame deep box inside the basement. (it was a weak hive, but seemed free of any noticeable pests before I brought inside). It has a clear entrance tube to the outdoors which I monitor every day. I've observed the workers dragging dead bees out from the hive and then leaving them in the tube. I find 5-10 newly dead bees in the tube every day. (I empty it every day). The actual rate be several higher/day - as some may be pushed to the outdoors.
Does anyone have any idea if this should be a concern? Or perhaps this is a natural mortality rate during winter.