Why bears hibernate? Redefining the scaling energetics of hibernation

Hibernation is a natural state of suspended animation that many mammals
experience and has been interpreted as an adaptive strategy for saving
energy. However, the actual amount of savings that hibernation represents,
and particularly its dependence on body mass (the “scaling”) has not been
calculated properly. Here we estimated the scaling of daily energy
expenditure of hibernation (DEEH), covering a range of five orders of
magnitude in mass. We found that DEEH scales isometrically with mass,
which means that a gram of hibernating bat has a similar metabolism to
that of a gram of bear, 20,000 times larger. Given that the metabolic rate
of active animals scales allometrically, the point where these scaling
curves intersect with DEEH represents the mass where energy savings by
hibernation are zero. For BMR, these zero savings are attained for a
relatively small bear (~100 kg). Calculated on a per-cell basis, the
cellular metabolic power of hibernation was estimated to be 1.3x10-12 ±
2.6x10-13 W/cell, which is lower than the minimum metabolism of isolated
mammalian cells. This supports the idea of the existence of a minimum
metabolism that permits cells to survive under a combination of cold and
hypoxia.