> This is only three answers from three bee keepers.  Can we not do better than this? :>)

Well, to me it's not how many but the caliber of the research. Ed Southwick was someone who really understood this topic. He was here at Bee-L in the beginning and died much too young, in 1995. He and Gerhard Heldmaier wrote

Bee colonies are able to tolerate more extreme cold temperatures than most mammals and birds. A bee cluster's cold-temperature tolerance of at least -80 C is as good as that of winter-hardy homeotherms (Southwick 1987). Large arctic foxes and Eskimo dogs can tolerate -80 C (Irving and Krog 1954), but the Alaskan Ptarmigan (Lagopus lagopus alascensis), a bird that has feathers even on its feet, has a cold temperature limit of about -50 C. Nude humans, in contrast, can tolerate near 0° air temperature for only an hour before body temperature begins to fall.

Although the mechanisms of adjusting temperature are different in bees than in birds and mammals, the resulting control is similar. Under a wide range of air temperatures, bee clusters maintain constant core temperatures around 34 C, not far from the 37 C found in many mammals. These observations point to convergent evolutionary paths in thermoregulation in organisms widely separated taxonomically. The system lends itself to further investigation.

Southwick, E. E., & Heldmaier, G. (1987). Temperature control in honey bee colonies. Bioscience, 37(6), 395-399.

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