>... sealing of the upper entrance when not needed is accomplished with an international standard wine bottle cork ...
When I transitioned away from upper entrances, I bought cap plugs similar to the attached to close the 1" diameter opening. Now they make a handy and relatively unobtrusive way to listen in on the colony.
I have had very few issues in our relatively mild and wet winter climate since adopting the condensing hive concept, maintaining a single 3/8" X 2-1/2" bottom entrance.
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