Warrés overwinter best
Besides allowing bee colonies to survive long, cold winters on minimal stores, Warré hives also offer other important design characteristics that improve overwintering success. It isn't only long-term confinement that can kill your bees. In other types of hives, they can perish rather quickly under certain conditions.
It's important to understand how bees behave inside the hive during the winter months. Bees don't hibernate. Although their metabolisms slow down, they remain awake and active all winter long in a tight "cluster". A winter cluster is usually about the size of a volleyball, although colony strength (population, and therefore cluster size) can vary. Now...a winter cluster is really quite active. First and foremost, the bees are rotating in and out of it in order to stay warm. The bees at the outer edges of the cluster will start to get cold after just a short time, so they'll rotate inward where there is more heat, and bees from within the cluster will take their places at the edges. The queen will remain somewhat centrally located within the cluster. Remember, now, that the cluster is living on and in between several wax combs. The bees cannot survive as several groups divided by combs that are over an inch thick, but rather only as one group packed tightly together. Therefore, the combs on which the cluster is located must be mostly empty (no capped honey), so that bees can occupy the combs' cells; thus creating one large group of bees that are divided by only the very thin wax "walls" that separate cells.
The second thing that's occurring within a winter cluster is that the bees are very slowly, but steadily, consuming their stores (stored honey). Heating the cluster requires energy, and honey is the fuel that supplies that energy. Since a cluster cannot live directly on combs that contain capped honey, it is only an outer portion of the cluster that can access the food supply. Bees that can access honey from the outer edge of the cluster will consume some before rotating back inside. A steady supply of honey is brought into the cluster and, once inside, is passed from bee to bee. In this way, the entire colony is fed.
In a vertical hive, such as a Langstroth or a Warré, it is the upper portion of the bee cluster that has the most access to the food supply. Speaking generally, the colony moves upward as it consumes its stores. Because a Warré hive is specifically designed (sized) to accommodate a cluster, all or nearly all of the stores will be consumed as the bees move upward. In comparing this to what can happen in a Langstroth hive, the Warré hive is much more efficient. A Langstroth hive is so large that it is not uncommon for stores to be passed up as the cluster moves upward. Typically, the bees will not reverse direction later on in order to access those stores. So, a Langstroth hive, which is highly ventilated instead of insulated, which encourages bees to consume large amounts of stores in order to stay warm, is also designed in a way that may cause bees to starve to death while there are still stores in the hive; often below them! And there's another problem with Langstroth hives...the frames. As a bee cluster moves upward in a vertical hive, their movement along the combs should be as unobstructed as possible. Any framed hive (including our own modified Warré hive) has large obstructions in the combs, between hive bodies. Think about a frame. The top bar of the typical frame is 5/8" thick and the bottom bar is 1/2" thick. Bee space between the top bar of a box below and the bottom bar of a box above is typically 3/8". When you add all of this up, it equals a space of 1.5" from the stores in a lower box to the stores in a box above. This big jump from one box to the next can be an insurmountable hurdle for bees when temperatures are very low. It is not uncommon that an entire cluster of bees is found in the spring, starved at the top of a framed box, just below another framed box filled with stores. In contrast, a Warré hive has only top bars, and those top bars are only 1 cm thick. The bees often leave only a tiny space between the combs of the box above and the top bars of the box below, and sometimes there are direct connections. The result is that instead of having to cross a space of 1.5" in order to access more food, the space is reduced to only slightly more than 3/8", which is a huge advantage for successful overwintering.
People frequently ask me about how Kenya top bar hives (KTBHs) compare to Warré hives. If you think about all of the things we've discussed so far on this page; about how bees cluster, how they move within the hive, how they feed, etc., common sense should tell you that just about every aspect of KTBH design flies in the face of what a bee-friendly hive should look like. Without even considering the fact that it's very difficult to ventilate or insulate a KTBH in order to prevent problems with condensation, one basic fact about KTBH design will almost ensure a colony's demise in very cold weather. Because the combs are oriented perpendicular to the walls, and because the bees can only move sideways, around each and every comb, in order to continue accessing their food supply, the bees must break cluster frequently in order to stay alive. In very cold weather, breaking cluster to move around combs in a KTBH is something that is actually a lot more difficult to do than crossing that 1.5" space in a framed hive that we talked about. It is in a KTBH, that bees are most likely to starve with stores right next to them. Why then, you might ask, are there so many advocates of KTBHs who swear that their bees overwinter in them without much problem? Well, let's examine that. There's a guy who is pretty smart and pretty well known in the beekeeping community, who frequently mentions the long, cold winters that his bees endure in northeast Nebraska. Now, it gets cold in NE, no doubt, but it also warms up significantly and with a great degree of frequency all winter long. It is when the weather warms up that the bees are able to break cluster and move to where they again have access to food. Many of us in the U.S. live in these more temperate zones, and many of us don't.
Let's do a couple of comparisons of one persons typical winter versus that of another person:
In Norfolk, NE, the mean temperature for January is 39.1 degrees F, with the average high being a very mild 47.3 F.
In Alpena, MI, the mean temperature for January is 17.6 degrees F, with the average high being only 26.4 F.
In Portland, OR, the mean temperature for January is 39.6 degrees F, with the average high being, again, quite mild at 46.4 F.
In Dayton, OH, the mean temperature for January is 26.0 degrees F, with the average high being just above the freezing mark, at only 34.1 F.
You may have heard of folks using KTBHs in Maine and overwintering with good success. Now, surely it's really cold way up in Maine, right? Well, that depends. Look closely at a map of the state of Maine and you'll find that a huge portion of the population there lives in areas where the temperatures are greatly influenced by the Atlantic ocean.
In Portland, ME, the mean temperature for January is 39.6 degrees F, with the average high being, again, quite mild at 45.4 F.
Just a short distance away, in Burlington, VT, the mean temperature for January is a brutal 16.3 degrees F, with the average high being a mere 25.1 F.
My advice about trying a KTBH is this: If you're confident that you live in an area where it gets warm enough, often enough, for your bees to be able to survive in one, then you may want to do it. Otherwise, you'll just be wasting your money.