I was privileged, this spring, to spend a day with Dr. Thomas Seeley and a small group of beekeepers in Durango, Colorado. The group was so small, in fact, that I was able to have several one-on-one conversations with Dr. Seeley as well as interact with him during our group discussions.
One of his topics was an explanation of the study he conducted to determine the hive cavity characteristics that are preferred by a honey bee colony. He made 256 bait hives and hung them in pairs on double power poles in the woods. There was only one difference between the hive boxes that made up each pair.
Mounting them on double power poles like this allowed the bees to easily spot both bait hives (also called swarm traps) and choose between them. Among other things, he tested for hive cavity volume, entrance size, and entrance location.
In his test, Dr. Seeley determined that honey bee colonies prefer a hive cavity volume of 40 liters, an entrance size of 2 square inches (shape doesn't matter), and an entrance location below the brood nest.
He suggested that these hive cavity characteristics are the most beneficial for those honey bee stewards who are endeavoring to practice Preservation Beekeeping. Or, to use Dr. Seeley's term, "Darwinian Beekeeping."
The thoroughness of his study was very impressive, as was his presentation of it.
In addition, there are Preservation Beekeepers who are weaving skeps and those who are building log hives. I am in conversation with beekeepers who are stewarding honey bees in each of these kinds of hive cavities and they are discovering that a 35 to 40 liter hive cavity is the bees' preferred volume.
This is why Bee Tree Preservation Hives have a 40 liter volume, a 2 square inch entrance opening, and the entrance located below the brood nest. But, the Preservation Hive accepts the same frames that are used in conventional Langstroth hives so that a currently hived colony can easily be moved to a Preservation Hive, and so that honey bee stewards that live in states with laws requiring honey bees to be kept on removable frames can still meet that requirement.