When the temperature drops below 57 degrees F the bees in a colony begin to form a loose cluster. At these temperatures bees may still be seen active at the entrance to the hive and inside the hive, but at a reduced level. By the time the temperature drops to 43 degrees F all the bees in the hive are in the cluster. Activity at the entrance and inside the hive will be negligible. As temperatures continue to drop the cluster will shrink in size as the bees pack themselves more tightly together to minimize heat loss.
Many beekeepers feed their hives during the fall to ensure the hive has enough resources to survive the winter. Top mounted liquid feeders are probably the most used method. (Boardman entrance feeders are mostly a warm weather feeder and also can induce robbing during the fall) Other beekeepers place candy(sugar) boards over the top of the hive. Both of these feeding methods are greatly effected by temperature and the bee's clustering behavior.
Once the bees are in cluster they will no longer be visiting liquid feeders; either top or entrance type. Of course each fall day as the outside air temperatures rise the bees may break cluster and begin using liquid feeders. However, the bees will not drink from liquid feed that is too cold.
I noticed that this morning the temperature had dropped to 44 degrees. I am sure the temperatures will warm back up again since it is only late September, but this is a warning that the effectiveness of liquid feeders is drawing to a close. So don't delay if you are planning to liquid feed; the window of opportunity is rapidly closing.
Candy boards are usually installed in early November when the bees are already in cluster. Otherwise, the bees would deplete this resource before winter arrives. In winter the bee cluster tends to rise vertically until they reach the top of the hive. If they have a warm winter day they may displace sideways. If the temperature is too low the tight cluster will not move. This is the time that the candy board is effective. When the cluster reaches the top of the hive it will naturally bump into the candy board and its food reserve. If that warm day does not arrive and allow the cluster to displace sideways then the candy board saves the day.
As an alternative to a candy board some beekeepers add a third brood box. They take the four outside frames of honey from the bottom brood box. The bees rarely utilize this honey since it is the habit of the cluster to rise vertically. These four frames are placed in the added third brood box. The recommended configuration is to place two empty, but drawn, frames in the center of the box surrounded by the four honey filled frames; two on each side of the empty frames. The empty frames are intended to provide room for the cluster.