Hi Alain,
In winter, if the bees go into hibernation and form a winter cluster, you will find that each hive looses weight at a constant rate. The rate likely depends on the size of the bee colony; it should be roughly proportional to the number of bees. Or, blame my intuition, maybe proportional to the cubic root of the number of bees, since they form a sphere?
A flat-lining behive (rate of weight loss = 0) means the colony is dead.
Snow will interfere with your readings as in this Danish study, where readings with snow cover were left out [Dropbox - Error - Simplify your life]
The figure shows weight drop in two consecutive winters, together with the loss rate (g/day) equal to the slope of each line. There is one line for each hive in both winters.
- Niels.