I heard an argument for covering the screened bottom boards today. This was the first explanation I've heard yet that gave me pause about leaving the bottom board wide open. The keeper said, that he was not closing up the bboards on his hives and wasn't having any issue. He went to help another beekeeper who covered the screen. This all happened in the early spring. What they observed was that the hives with the screen blocked had brood lower down in the hive body compared with the screened hives. They postulated that it was because the hive could be kept warmer earlier in the brood rearing season allowing the queen to lay lower sooner. Thoughts?