The cluster will expand and contract in accordance with the ambient temperature. As it gets colder, so the cluster will tighten, and as the temperature rises so the cluster expands, until, on a warm March day, the cluster breaks up sufficiently for the first flights to be taken. These may only be cleansing flights, as the bees have been enclosed all Winter, and unable to defecate.
Remove mouse guards and close down the cover board to the brood box. Mouse guards can act as very efficien pollen strippers, removing the pollen from their legs before they can enter the hive
If the day is particularly warm, loads of pollen can be seen being carried into the hive. This means that the bees have been foraging on perhaps crocus, snowdrops, aconites, willow or hazel, and is a pleasing sight to the beekeeper, as it signifies that the colony has safely come through the Winter, and has tiny mouths in the hive to feed.
It is still too cold however for the hive to be opened.