>The importance of this has long been understood.
When we first started wintering because of increased package prices, we used a fairly large slot in the inner cover. When the US/Can Border closed suddenly and we needed to winter everything, we didn't have enough inner covers, so wintered the extras without an upper entrance. As the operation grew a couple hundred hives each year, we continued without an upper entrance on those colonies. Worked well and we felt those without, actually graded better on the 1st of April. They definitely had increased brood. Then about year 5, we had a really mixed spring with a lot of temperature swings and several freezing rains. Those with upper entrances had average losses and the usual distribution of colony strength. Those without, were either very alive or very dead. Lost over 50% of those without the upper entrance. It especially stood out in yards where we had both.
As we had ventured down that road, I had been discussing upper entrances with Dr Don Nelson, Apiculture Researcher at the Agriculture Canada Research Station, Beaverlodge, AB. He had warned me that this had been their experience. Certain years, it would bite you. Hence forth, we have always used a upper entrance, but have reduced it to 1/2" wide and 1/4" high with wind deflection. We see virtually the same spring build up as those colonies without an upper entrance, but have never again experienced the mortality. We also reduce the bottom entrance to its smallest opening. As others have mentioned, good top insulation is also key especially here where we get stretches of minus 40C/F.
David Tharle
T'N'T Apiaries
Ardmore, Alberta
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