Once again the bees showed me that they are fully capable of controlling the micro-climate and micro-ecology of the hive if we will just provide them with a hive cavity that allows them to do so, and then leave them to it.
By fanning in such a way that they cause air to move across the entrance holes, the bees lower the air pressure outside the entrances which causes the warm air in the hive, on a hot day like this, to be drawn out through the holes. (Remember your 6th grade Physical Science?) Because the Bee Tree Hive base is ventilated, air can be drawn in at the bottom to replace the escaping hot air.
As I continue to learn how to provide honey bees with the ability to live like they live in the wild, rather than being invasive and interventive in my beekeeping practices, the bees keep showing me what they are capable of.